Taxonomy of the Garlic (Allium sativum L.) according to Cronquist System
Dominium/SuperKingdom: Eucariota Whittaker & Margulis,1978
Plantae Haeckel, 1866
Subregnum/Subkingdom : Viridaeplantae Cavalier-Smith, 1998 (Green Plants)
Superdivisio/Superdivision: Spermatophyta Gustav Hegi, 1906
Divisio/Division or Phylum: Tracheophyta Sinnott, 1935 ex Cavalier-Smith, 1998 -
Subdivisio/Subdivision: Magnoliophytina Frohne & U. Jensen ex Reveal, 1996
Classis/Class: Liliopsida Brongn., 1843
Subclassis/Subclass: Liliidae J.H. Schaffn.,1911
SuperOrdo/SuperOrder: Lilianae Takht., 1967
Ordo/Order: Amaryllidales Bromhead, 1840
Familia/Family: Alliaceae J. Agardh, 1858
Subfamilia/Subfamily: Allioideae Herb., 1837
Tribus/Tribe: Allieae Dumort., 1827
Subtribus/Subtribe: Alliinae Parl, 1852
Genus: Allium L. 1753
Species: Allium sativum L. 1753
Taxonomy of the Garlic (Allium sativum L.) according to APG System
Clade: Eucariotae Whittaker & Margulis,1978
Plantae Haeckel, 1866
Clade: Unassigned monocots
Familia/Family: Alliaceae J. Agardh, 1858
Subfamilia/Subfamily: Allioideae Herb., 1837
Tribus/Tribe: Allieae Dumort., 1827
Subtribus/Subtribe: Alliinae Parl, 1852
Genus: Allium L. 1753
Species: Allium sativum L. 1753
The ancestry of cultivated garlic is not definitively established. According to Zohary and Hopf "A difficulty in the identification of its wild progenitor is the sterility of the cultivars", though it is thought to be descendent from the species Allium longicuspis Regel, 1875 , which grows wild in central and south-western Asia.Allium sativum L. 1753 grow in the wild in areas where it has become naturalised. The "wild garlic", "crow garlic", and "field garlic" of Britain are members of the species Allium ursinum L. 1753, Allium vineale L. 1753, and Allium oleraceum L. 1753, respectively. In North America, Allium vineale L. 1753 (known as "wild garlic" or "crow garlic") and Allium canadense L.1753, known as "meadow garlic" or "wild garlic" and "wild onion", are common weeds in fields. One of the best-known "garlics", the so-called elephant garlic, is actually a wild leek (Allium ampeloprasum L. 1753), and not a true garlic. Single clove garlic (also called Pearl garlic or Solo garlic) also exists, originating in the Yunnan province of China.
Statistical and economical data
The world production of garlic has been attested in 2009 on 16.593.073 tons on a surface of 1.242.674 hectares (FAO, 2009). The main producers are: China (12,575,036 t), India (645,000 t), South Korea (375,463 t), Russia (226,670 t) and United States of America (194,230 t).
Europe is interested for 25% and has produced 304,040 t on 40.850 hectares; between the Member States of UE the Spain predominates that, with 142.400 t, produces 47% of garlic of all the European Union. Italy follows with 26,958 t (10%) and France with 19,500 t (9%). In table 1, the data regarding the garlic are reported for the main farmer of the world, with refer to the surface, the amount of production (in ponderal terms and in economic value) and to the yield.
| Table 1 Surface expressed in ectars (ha), quantity of production of bean dry in tons (t), value of the production noticed in thousands of dollars ($1000), yields, expressed in tons per ectar (t/ha), for the main Countries of the world (FAO, 2009).
|| Surface (ha)
| Quantity (t)
|| Value ($1000)
United States of America
In the 2008, the Italian production was 26.800 t, obtained on a surface of 3.032 ectars (Table 2).
| Table 2 - Surface and productions of garlic in Italy (ISTAT, 2008).
Emilia and Romagna
Allium pekinense Prokhanov, 1929 is one of the synonyms of the garlic.
The common names with which this species is named in the world are the following:
- ARABIC : ثوم Thawm, Thoum, Thum, Toom, Toum, Saum.
- ARMENIAN : Սխտոր Sekhdor.
- BENGALI : রসুন Rasun.
- BULGARIAN : Чесън.
- BURMESE : Chyet thon phew.
- CHINESE : 蒜 Suan, 大蒜 Da suan (medicinal name), Da suan tou (garlic bulb).
- CROATIAN : Čenjak.
- DANISH : Hvidløg.
- DUTCH : Knoflook.
- ENGLISH : Garlic, Common garlic.
- FINNISH : Valkosipuli.
- FRENCH : Ail, Ail blanc, Ail commun, Ail cultivé, Ail de printemps, Ail rose sans bâton.
- GERMAN : Echter Knoblauch, Knoblauch, Gemeiner Knoblauch, Gewöhnlicher Knoblauch.
- GREEK : Σκόρδα Skorda, Σκόρδο Skordo, Skordon, Skortho.
- GUJARATI : લસણ.
- HEBREW : שום Shoum, Shum.
- HINDI : Lahasun, लहसन Lahsan, Larsan, Lasun.
- ITALIAN : Aglio, Aglio comune.
- JAPANESE : ガーリック Gaarikku, ニンニク Ninniku.
- KANNADA : Bellulli, Lashuna.
- KHMER : Khtüm sââ.
- KOREAN : 마늘 Ma nul.
- LAOTIAN : Kath'ièm.
- MADURESE : Bhabang poté.
- MALAY : Bawang putih (Indonesia, Java), Bawang puteh.
- MALAYALAM : Vallaipundu.
- MARATHI : Lasuun.
- NEPALESE : Lasun.
- NORWEGIAN : Hvitløk.
- PERSIAN : سیر Seer, Sir.
- POLISH : Czosnek, Czosnek pospolity.
- PORTUGUESE : Alho.
- PUNJABI : Lasun, ਲਸਣ Lasan.
- RUSSIAN : Лук-чеснок Luk chesnok, Чеснок Chesnok, Лук посевной Luk posevnoi.
- SANSKRIT : Lashunaa.
- SERBIAN : Beli luk.
- SINHALESE : Sudulunu.
- SLOVENIAN : Česen.
- SPANISH : Ajo, Ajo comun, Ajo vulgar.
- SUNDANESE : Bawang bodas.
- SWAHILI : Kitunguu saumu.
- SWEDISH : Vitlök, Vitloek, Hvitlök.
- TAGALOG : Bawang.
- TAMIL : Vellaypoondoo, Vellaippuuntu, Wullaypoondoo.
- TELUGU : Vellulli.
- THAI : กระเทียม Krathiam, Hom tiam.
- TURKISH : Sarımsak, Sarmesak, Sarmusak.
- URDU : لھسن Lehsun.
- VIETNAMESE : Tỏi.
- VISAYAN : Ahos, Ahus
Botanical characteristics, biology and physiology
Botanically the garlic is a herbaceous perennial plant, but it is practically cultivated like annual (figure 1a).
The leaves (figure 1b) are basal, wrapping the stem and, on the contrary of that it happens in the onion, they do not work such as supply organs. The leaves are formed tangling round up it for along feature as well as that often they come exchanged like a cylindrical stem. The part of the not wrapping leaf have a linear form and it is wide till 3 cm, ending with one spiky tip and can catch up a total length of 80 cm.
The stem is a small plate of few millimetres thick, 2-3 cm long and 1-2 cm wide (figure 1c).
When come up, the flowers are carried from floral steles tall from the 40 up to 80 cm that carry to the top an umbel inflorescence (figure 1d). The flowers are small and they are carried on court peduncle. All the flowers, forming a head named spate, are also edible and they are most often consumed while immature and still tender being milder in flavour than the bulbs. The flowers are white tending to the red-pink and often they are not opened and they often abort still in bud.
Garlic is a plant carrying bulbs (figure 1e), cultivated for its flavour.
The garlic plant's bulb is the most commonly used part of the plant. With the exception of the single clove types, the bulb is divided into numerous fleshy sections called cloves (figure 1f). The bulbs are covered with sterile membranous leaves named sterile tunic of different colour and having exclusively a protecting function (figure 1g).
The clove, that it represents the multiplication organ, is attacked directly to the stem. Each bulb contains from 6 to 14 cloves tight around.
The cloves freshly harvested are not able to germinate being, in fact, in a state of dormancy. To germinate they need to go through a series of physiological stages related to weather.
The cloves are used for consumption (raw or cooked), or for medicinal purposes, and have a characteristic pungent, spicy flavour that mellows and sweetens considerably with cooking.
The seeds (figure 1h) are formed very rarely. They are obtained from fertile inflorescences. The seeds are very important in genetic improvement programs in order to fix useful traits selected for progeny, according to the concepts of heritability (the fraction of the total phenotypic variance due to additive gene action).
Garlic is supplied from 40 to 60, superficial roots such as a rope that do not get a deeper knowledge beyond first 30 cm of soil. The root cluster attached to the basal plate of the bulb is the only part not typically considered palatable in any form.
The sticky juice within the bulb cloves is used as an adhesive in mending glass and porcelain in China. Dating back over 6,000 years, it is native to Central Asia, and has long been a staple in the Mediterranean region, as well as a frequent seasoning in Asia, Africa, and Europe. It was also highly-prized mostly in Egypt, it was even used as currency.
Figure 1 a) garlic cultivated in open field; b) garlic plants, whose leaves are basal and wrapping the stem; c) bulbs cultivated while growing up in the open; d) typical inflorescence of the Liliaceae; e) plate-stem with cloves narrow and winding. We also show two young inflorescences most often consumed while they are immature and still tender, such as for Sulmonas red garlic variety; f) closeup of a bulb with cloves wrapped in sterile leaves (tunics) that give color to garlic; g) garlic seeds obtained from fertile inflorescences.
The bulb crop to maturity, when the leaves are partially dried, is at the dormant state, that is, unable to even germinate if placed under thermal and humidity favorable. The length of the period of dormancy depends on the variety and the storage temperature of cloves.
When the dormancy was overcome thanks to a suitable storage, place the clove into the soil gives the roots and sprouts at the expense of reserve substances accumulated in it. The phase of germination can last from a few days (spring plants) to 30-45 days (autumn plants with low thermal regimes).
After germination you have the progressive emission of the leaves, in variable number from 8 to 20, according to the cultivar, the climatic conditions and the age of the plant.
The bulbification, that is the formation of bulbils that differentiate in the axils of the leaves with foil, is induced by high temperatures and long day. The threshold values of these factors vary according to the variety.
The size of the future bulb depend on the number and size of the bulbils that constitute it, and these characteristics are related, respectively, with the number of leaves (the bulbils differ fact axils of leaves with foil) and with the leaf surface (proportional the duration of the vegetative phase and to the vigor of the plant). The little dormant varieties planted in the fall, having a long duration of vegetative growth, have higher productive potential.
The bulbification ratio, that is the ratio between the maximum diameter of the bulb and the minimum diameter of the collar, increases from about 1.2 during the vegetative phase to 5 or more in the mature plants.
The beginning of the bulbification can be externally identified when the bulbification ratio is ≥ 2.
After the production of the leaves, the meristematic apex positioned at the center of the bulb-mother disk may abort or develop in the flowering stem. The formation of the flowering stem depends on the variety and environmental conditions: the varieties with strong dormancy and bulbification relatively early have a greater predisposition to bloom which is priviliged by the storage of the mother bulbs at very low temperatures (from -2 up to 2 °C) and temperatures of 0-10 °C combined with long day at the beginning of the bulbification.
In practice, the local populations have been selected to have a low aptitude for the formation of the flowering stem. In the case in which it is formed, the flowering stem is rapidly suppressed to avoid competition with the cloves in formation or growth. In this case, the basal part of the flowering stem, however, remains at the center of the bulb and dries.
In the final phase of the cycle, the leaves begin to turn yellow and dry progressively until the collar loses turgidity determining the sway of the leaf apparatus under its own weight.
The harvest, generally, takes place when the leaves are yellow or dry them in the upper third and with the collar still partially swollen.
The cycle of garlic is very long in relation to the climatic conditions and the variety. It start from October to February and ends from June up to July.
Photoperiodic and temperature requirements
The garlic in the resting phase can withstand very low temperatures (down to - 15 °C).
The dormancy of bulbils is stopped by relatively cool temperatures: therefore, the optimal storage temperature of the bulb-mother is 7 °C for about 8-16 weeks, although the optimum temperature for induction to bulbificazione is 2-4 ° C. The dormancy is instead induced or maintained by both the low (0-1 °C) by high (18-25 °C) temperatures.
Growing degree days (GDD), also called growing degree units (GDUs), are a heuristic tool in phenology. GDD are a measure of heat accumulation used by horticulturists, gardeners, and farmers to predict plant and animal development rates such as the date that a flower will bloom or a crop (such as the garlic) reach (physiological or commercial) maturity.
In the absence of extreme conditions such as unseasonal drought or disease, plants grow in a cumulative stepwise manner which is strongly influenced by the ambient temperature. Growing degree days take aspects of local weather into account and allow gardeners to predict (or, in greenhouses, even to control) the plants pace toward maturity.
Unless stressed by other environmental factors like moisture, the development rate from emergence to maturity for many plants depends upon the daily air temperature. Because many developmental events of plants and insects depend on the accumulation of specific quantities of heat, it is possible to predict when these events should occur during a growing season regardless of differences in temperatures from year to year. Growing degrees (GDs) is defined as the number of temperature degrees above a certain threshold base temperature, which varies among crop species. The base temperature is that temperature below which plant growth is zero. GDs are calculated each day as maximum temperature plus the minimum temperature divided by 2 (or the mean temperature), minus the base temperature. The relation is:
Taverage = (Tmax + Tmin)/2
For the garlic, the temperature base is:
Tbase = 0 °C
GDUs are accumulated by adding each days GDs contribution as the season progresses.
GDUs can be used to: assess the suitability of a region for production of a particular crop; estimate the growth-stages of crops, weeds or even life stages of insects; predict maturity and cutting dates of forage crops; predict best timing of fertilizer or pesticide application; estimate the heat stress on crops; plan spacing of planting dates to produce separate harvest dates. Crop specific indices that employ separate equations for the influence of the daily minimum (nighttime) and the maximum (daytime) temperatures on growth are called crop heat units (CHUs).
GDD are calculated by taking the average of the daily maximum and minimum temperatures compared to a base temperature, Tbase, estimated of 0 °C for garlic). As an equation:
|(Taverage - Tbase )
The GDD (acronymus of Growing Degree Days), the daily sum of the temperature degrees during the vegetative phase must be equal to 95 and it by the equation above
If the mean daily temperature is lower than the base temperature then GDD=0.
In practical terms, if the thermal sum is greater than zero means that the temperature was on average higher than that required for optimal growth of the species , while if the thermal sum is less than zero then the temperature was too low . Its value can be put in relation to other parameters, such as the irrigation necessary.
Obviously if the sum thermal deviates too much from zero occur risks for the crop. It is rather the opposite is true , that is, a sum thermal near or equal to zero does not exclude changes in temperature, positive and negative, such as to damage the crop.
During their life cycle plants require a certain amount of heat (energy) for the various stages of their growth. The vegetative cycle duration is generally shorter the greater is the amount of energy received which is in turn correlated with the average daily temperature . You can go back then , with a certain approximation, the duration of the life cycle , knowing the amount of useful degrees of temperature for the day and the total requirements required by the plants. In addition, you may provide any advances or delays of the period of cycle growth or the bulb maturation, for example, as a function of seasonal trends warmer or colder than average.
If the daily average temperature is equal or less to vegetation zero, GDUs are not accumulate.
In synthesis and for specifying better, a degree day is a measure of heating or cooling. Total degree days from an appropriate starting date are used to plan the planting of crops and management of pests and pest control timing. Weekly or monthly degree-day figures may also be used within an energy monitoring and targeting scheme to monitor the heating and cooling costs of climate controlled buildings, while annual figures can be used for estimating future costs.
A degree day is computed as the integral of a function of time that generally varies with temperature. The function is truncated to upper and lower limits that vary by organism, or to limits that are appropriate for climate control. The function can be estimated or measured by one of the following methods, in each case by reference to a chosen base temperature:
A zero degree-day in energy monitoring and targeting is when either heating or cooling consumption is at a minimum, which is useful with power utility companies in predicting seasonal low points in energy demand.
- frequent measurements and continuously integrating the temperature deficit or excess;
- treating each day's temperature profile as a sine wave with amplitude equal to the day's temperature variation, measured from max and min, and totalling the daily results;
- as above, but calculating the daily difference between mean temperature and base temperature;
- as previous, but with modified formulae on days when the max and min straddle the base temperature.
Heating degree days are typical indicators of household energy consumption for space heating. The air temperature in a building is on average 2 °C to 3 °C higher than that of the air outside. A temperature of 18 °C indoors corresponds to an outside temperature of about 15.5°C. If the air temperature outside is 1 °C below 15.5 °C, then heating is required to maintain a temperature of about 18 °C. If the outside temperature is 1 °C below the average temperature it is accounted as 1 degree-day. The sum of the degree days over periods such as a month or an entire heating season is used in calculating the amount of heating required for a building. Degree Days are also used to estimate air conditioning usage during the warm season such as in the greenhouse crop protection.
The bulbification is induced by high temperatures (18-20 °C) and from day long.
The minimum duration of the day depends on the place of variety origin. The minimum thresholds for the duration of the day effective for bulbification garlic should be as follows:
- in tropical regions the length of the day should be 11.5 to 12.0 hours;
- in the South Mediterranean should be 13.0 to 13.5 hours;
- in the Central Mediterranean must be 14.0 to 14.5 hours;
- in the North Mediterannean the length of the day should be 15.0 hours.
Flowering is favoured by long days and temperatures low enough, however, below 18 °C.
The photoperiodic and thermal regime during storage and field also leads to complex effects on the growth and development of garlic, with obvious repercussions on quality aspects. For example, relatively low temperatures during storage of the mother bulbs, followed by low temperatures and
short day in the field (after the induction to the bulbification) predispose the plant to the formation of side shoots and bulbils and therefore of malformed bulbs; photoperiod long and high temperatures, immediately after the planting, promote the formation of a bulb consisting of a single clove of large sizes.
The garlic, being a plant sexually sterile, is unable to produce vital seed, for which it is multiplied by vegetative via (bulbils said improperly "seeds").
This has encouraged the spread of ecotypes, that is local populations, that were cultivated for a long time in the same area were mildly selected (for example, during the genetic selection, elimination of out kind individuals, not required by the market, and sick ones) and are now well adapted to certain climatic conditions and well differentiated between them.
The local people, who often take the noun or the adjective of the origin place (for example, between those Italian: White of Piacenza, Red of Sulmona, Genoa Garlic, White of Piedmont, Veneto, Pescia, Fucino, Neapolitan, Sicilian), are commonly called varieties and are now quite stable but relatively heterogeneous.
The garlic varieties cultivated can be classified into 8 groups according to their biology (need in the cold for the elimination of dormancy and growth start of the axillary apex, photoperiodic requirements for bulbification) and their morphology (colour of the tunics, structure of the bulb).
Group 1 - large variety bulbs, do not form flowering stem; variable colouring with outer skins from white to mauve, bulbils from ivory white to violet. 75% of French production and about 10% of Spanish and Italian are to be included in this grouping;
group 2 - variety in medium or small bulbs, do not form flowering stem; dormancy high; staining of cloves and tunics fairly constant from white to ivory white. About 80% of Italian production, 15% of French production and small amounts of Spanish production have the varietal characteristics of this group;
Group 3 - bulb varieties of medium size, form flowering stem; dormancy medium to strong, highly variable coloration with tunics from white to mauve and cloves from ivory white to purple, sometimes striated white/red. About 10% of French production and almost all Spanish varieties fall into this group;
group 4 - varieties that have some needs in cold and require a reduced day length for bulb growth. The types of tropical mountain grown in Mexico and Peru have characteristics of this group;
5th group - varieties that have no requirement for cold and require a short day length for bulb growth. The types of tropical lowland belong to this group;
6th group - spherical variety with small bulbs formed by 4-6 cloves of good structure, often in dark red robes. Types common in the Far East belong to this group;
7th group - varieties similar to those of group 6, but with an open structure like many Chinese varieties;
8th group - cultivar similar to those of group 1, but with flowering stem, as most of the Japanese varieties.
There are numerous cultivars mostly derived from selection with the local populations. Simply we can distinguish them in garlic with white tunic and with red tunic.
Varieties with white tunics, with silver-white tunics, regular bulbs with 14-15 cloves, late, to strong dormancy, suitable for autumn plants. They are the most common types (representing approximately 90% of the garlic grown) due to the considerable size, good and constant production and adaptability to different environmental conditions:
- White of Piacenza or Ottolini garlic (figure 2);
- Big Venetian;
- White of the Fucino;
- White of Naples (figure 4);
- White of Calabria;
- White Polesano;
- White of Voghiera (figure 5), white bulbs with bright and uniform.
Varieties with a pink tunic, with bulbs less regular than white and consist of several bulbils (more than 20). It is not much preservable for which it is consumed fresh. It is earliest of the white garlic of about 20 days and it has less than the dormancy characteristics. It has limited diffusion and it is considered less valuable of the white garlic. At this varieties belong to the following types:
- Pink Neapolitan;
- Garlic of Vessalico (figure 6);
- Pink of Agrigento (figure 7).
Varieties with a red tunic:
- Red of Sulmona (figure 8 and figure 9), it is an ecotype that has intermediate characteristics between the two groups because it has the outer skin of the bulb white, while those of cloves of purple, this ecotype always develops the flowering stem that is removed and eaten fresh.
- Red of Nubia: from the name of a district of Trapani, it is Slow Food presidium. The bulb typically consists of twelve cloves, with white outer tunics and the internal tunics of bright red. It is traditionally packaged in braids for about one hundred bulbs. Starting from the local population in the past decade has begun a systematic selection that gave rise to clonal varieties are characterized by a more uniform morpho-biological characteristics, good productivity, good storage, no virus thanks to the work of restoration techniques facilitated by in vitro culture. An example of what is now called the variety Serena White of Piacenza.
The main varieties officially listed in the Italian National Register and selected from national ecotypes are:
- White of Piacenza" (figure 2), medium-late varieties of garlic (maturing from July 7 up to 15), medium size and regular, average production of about 10 t/ha of dry matter, long-term storage in the refrigerator, pronounced flavour, planting in October. It is perhaps the best white garlic good size grown in Italy, famous for its quality of taste and good shelf life. It contains high amounts of allycin and essential oils that make it an excellent aid against many diseases such as hypercholesterolemia and against the increase in blood pressure;
- Red of Sulmona (figure 8 and figure 9), a variety with white bulb and with red cloves, the presence of flowering stem , medium-early maturing (20-30 June), medium size and smooth, discreet productivity (6.5-7 t/ha of dry product), good storage in the refrigerator, spicy aroma and flavour, planting in late November to December;
- Serene, a medium-late variety of garlic (maturing July 10 to 17), virus-free, regular and large size, good production potential (12-14 t / ha), long-term storage in the refrigerator, pronounced flavour, sowing in October;
- Cristop, of French origin, garlic white medium-late (maturing July 5 to 15), the presence of the flowering stem , size medium-large and irregular, good production, media storage in the refrigerator, pronounced flavour, sowing in October. The variety is free from viruses.
Figure 2 White of Piacenza, l ecotype more widespread in Italy.
Figure 3 - "White of Monticelli" has obtained the designation of protection originated under Regulation (EEC) No. 2081/92. The area of production and packaging of this garlic ecotype falls in the province of Piacenza and
includes the entire territory of the municipalities of Besenzone, Cadeo, Caledon, Caorso, Castelvetro, Cortemaggiore, Fiorenzuola Gossolengo, Gragnano Trebbiense, Monticelli, Piacenza, Podenzano, Pontenure, Rottofreno, Sarmato, San Pietro in Cerro, Villanova and part of the territory of the municipalities of Agazzano Alseno, Borgonovo Val Tidone Carpaneto Piacenza, Castell'Arquato, Castel San Giovanni, Gazzola, Ponte dell'Olio, Rivergaro, San Giorgio Piacentino, Vigolzone.
Figure 4 White of Naples, a cultivar characterized by pink tunics and a high content of essential oils. Garlic di Naples mature in June and traditionally it is harvested in occurs on the religious feast of St. Anthony of Padua, June 13. After harvesting, the bulbs are cleaned and left to dry for about ten days until June 24 feast of St. John, we proceed interweaving of traditional plaits, which can be found in every Naples home.
Figure 5 White of Voghiera, a cultivar of Ferrara, which produces more than 50% of the production of the whole Province. The product has a good size and homogeneous, the colour is bright white and the yield per hectare is good and now coming up to about 100 q. In 2000, it were formed the Consortium of Producers of the Voghieras Garlic. The objectives of the Consortium are: to treat the study of the method of production, reducing costs and streamlining processes, promote agricultural experimentation and research programs directed to the enhancement of the garlic; promote agricultural experimentation and research programs directed to the productive reconversion of associated companies for retrofitting; cure, in collaboration with national, regional and local Services, the diffusion of data and information.
Figure 6 Vessalicos Garlic is a cultivated variety in the 11 municipalities that make up the territory of the Arroscia Valley. The name is related to the Fair (Fera) which is held in the valley in the municipality of Vessalico (a document Liber Decretorum Communitatis Vessatici makes it back to the year 1760). The main features of this variety are the intense aroma accompanied by a delicate taste, garlic is a very digestible and has a good shelf life. These characteristics are given by the mild climate (the Arroscia Valley lies at the foot of the Alps, at the same time still suffers from the influence of the climate of the Ligurian coast) and from soils particularly suited to this crop. Vessalicos Garlic has a compact bulb consists of an average of ten cloves, with the outer tunics of white-pink (with red-purple streaks just harvested) and the cloves in white. This variety of garlic has not inflorescence.
Figure 7 Agrigentos Pink Garlic has outer tunics white-pink. The shape of the bulbs is huge, with more than 20 segments, smaller and less regular than white garlic, fresh and consumed mainly because it has less shelf life, about 3-4 months.
Figure 8 "Red of Sulmona" is an ecotype grown for centuries in Abruzzo (Peligna Valley) in the province of L'Aquila (whose main centre is Sulmona). It is a product of excellent quality, well appreciated in the market, which has given rise to high export flows, but has followed the downward trend of the culture in Italy, where the surfaces are reduced and are now estimated at about 150 hectares. The marketable production is 10,000 q of dry product with a value of approximately 2 million. In this situation, was born in July 2009, the Consortium of Producers that promotes all efforts to defend, protect, enhance and commercialize garlic Red of Sulmona. The results achieved in just 3 years of work demonstrate that the path is re-launching and qualifying the production Red of Sulmona garlic.
Figure 9 The typical braid of the variety "Red of Sulmona" garlic. In fact, this particular variety of garlic is processed in braids with 54 heads of two lines, which are then hung in the pantry, such as it is done with the chilli pepper. The "Red of Sulmona" has characteristics that qualify the national level. Its name comes from the colour of the last tunic that protects the clove, which is a nice red colour intense wine, with homogeneous diffusion and strong, but it can also yellowish-white streaks more or less marked. The conformation of the bulb is regular and well tightened its consistency, for which are absent the supernumerary cloves or those extratunicates. Maturation takes place between the third week of June and the first half of July, in an intermediate period of harvest between the pink garlic of the Southern Italy and those white ones of the North. The shelf life at room temperature is high, so that the bulb is kept firm and compact until the following spring and they have a delayed pre-shooting. The ecotype is known in Italy for the high spiciness and aroma due to its high content in essential oils typical of garlic (disulphide and diallyldisolphure), which provide both a flavour organoleptic specific that high pharmacological properties. Finally, it is the sole Italian variety in which the regular issue of the flowering stem, which can be eaten both fresh both in oil.
Garlic hailing from abroad
Pink of Lautrec French garlic (figure 10)
Probably originated from a local mutation of plants. Legend has it that the plants were given in exchange for a meal to be a pilgrim without money passed through Lautrec. The pink garlic of Lautrec French is sometimes marketed in Italy as pink garlic. It is a misconception, because the garlic with trade mark named Label Rouge since from 1966 - the first certification system for quality products applied in France - comes from an area of about 360 acres on the slopes of clayey limestone of the Tarn, where Lautrec is the most important City.
Area with mild climate, thanks to the double influence of the Mediterranean Sea and the Atlantic Ocean where the pink garlic is cultivated since the Middle Ages. Since 1996 this garlic obtained the IGP trade mark. The features of this product certainly justify the price high: sweet and intense aroma without being aggressive, with low persistence over time, therefore can be used without problems known as social consequences. The slogan with which it is advertised Ne dites pas ail avant de l'avoir gouté (do not say garlic up to you have it tasted).
The heads of garlic are regular and full, with well separated cloves, strong and suffused pink colour, listed by darker signs.
The plant must be removed from the ground whole, without being deprived of leaves and roots, and hung to dry in a ventilated and shaded, where will lose a quarter of its weight. Only when the cloves are ready, the roots and the leaves are eliminated, except the last which allow to keep the head cohesive without hiding the colour.
At this point we package in manouille, not in braids, but in bunches with stems of different lengths side by side so as to obtain the same effect of the braids. The drying process is natural and takes long time, but allows to keep the cloves still full from year to year.
To give garlic its distinctive characteristics are essentially four elements:
- The starting material.
- The mild climate that allows for early cultivation.
- The nature of the soil clayey limestone.
- The conformity with the instructions of cultivation indicated by the product specification.
The seeds produced by flowers are sterile so the pink garlic is grown only from the cloves, which must be placed in the ground in the months of December and January. At the beginning of the month of June provides, through plant to plant, to remove the flowering stem. The harvest is make at the end of the month.
In the cultivation of the crop, the main operation that weed control should be carried out with a light hoeing the soil and eliminating manual. The hoeing also serves to break the crust of the soil that can be formed with the swing action of the rain, keep soft and permeable soil, interrupt the capillary rise of water from the deep layers.
The irrigation is carried out only during periods of water scarcity, always wet the foot of the plants with small quantities of water, and never saturate the soil. Do not water the crop in the vicinity of the harvest.
All operations should be conducted avoiding to compact the soil by pounding.
Figure 10 Pink of Lautrec French garlic. We observe the typical braid adopted for this French variety, obtained by tying bunches of garlic with different length of the stems.
A special type of garlic is that belonging to the range Black Garlic product by the English organization. Black garlic (Figure 11) is obtained by letting the garlic fermented at high temperatures for a few weeks, it tastes spicy and balsamic, but leaves no aftertaste garlic typical and bad breath, it has double the amount antioxidants, compared to the normal garlic, low in fat and is rich in natural sugars. In general, the strength of this product is that its production process is completely natural, without the use of preservatives or other chemical additives added, presenting a long shelf life. Moreover, its essential trace elements are multiplied exponentially (up to 10 times!) by the fermentation process. This manufacturing process finish in approximately thirty days and decreases 97% the typical pungent flavour. The final product has a sweeter flavour profile, reminiscent that of a plum.
The black garlic is used as an ingredient in all kinds of dishes, like a spice, although it can also be eaten raw. The range of the Black Garlic consists of bulbs (both single and double pack), peeled in jars from 50 to 150 grams and will soon be introduced on the market the cream of black garlic. The company currently imports wholesale product from the United States and then package it in the United Kingdom (Figure 12). Black Garlic supplies when the chains Tesco, Waitrose, Sainsbury's and Budgens, as well as many individual firms in England. The number of wholesalers is continuing to grow.
Figure 11 Garlic of the range od Black Garlic, presented to the Fruit Logistica in Germany (Berlino, february 8-10, 2012).
Figure 12 Method of packaging of the range Black Garlic.
Between the end of July and throughout the month of August 2013 has arrived in Italy Chinese garlic, without, however, meet with great enthusiasm, as the prices are lower than garlic of national origin and to import Spanish, although not in a significant. It also notes a growing alienation of the consumer against Chinese garlic, although the price is lower, the preference is always more to Italian products and the Spanish one. By now, the biggest consumers of Chinese garlic are the countries of Northern Europe, mainly Britain.
The Spain is the main country from which the Italy imports garlic. The Spain this season has produced a good quality product and good gauge of the type variety Spring . However, the contrary, the varieties of garlic traditional white again present problems of drying and curing, due to the phenomenon known as "Waxy Breakdown", attributable to infection by Fusarium proliferatum , now generalized and evident in three producing countries (Spain, France, and Italy). This rot is still widespread exclusively white garlic and not the kind of red or pink.
Quality problems, but of a different nature, they are also found on the variety "Morado" in Spain, with the presentation of bulbs quite irregular and deformed with few coats of finish and colour of the coating films of the segments very faded and tending to white. In practice, the characteristics that differentiate these varieties from garlic white this year are less obvious and so the market is experiencing a decrease in the selling price and low demand.
The average import price in 2013 varies around 1.00 to 1.50 /kg, depending on the caliber and quality class. The demand is still low and the interest in the product is really non-existent.
The future prospects are the biggest problem and the great unknown of the segment. First of all, this year there will be enough unsold product and the average farmer will surely be tempted to replant it, a likely result of a further increase in production not only in Europe but also in China, where the great production this season has created the same issues of European market.
In addition, the phenomenon of the spread of "Waxy Breakdown" is moving more and more towards the choice of farmers variety of early type and is creating some concern in the purchase of seed certified free of viruses which, however, does not guarantee safety production and the subsequent placement of this market. Until September of 2013 are still available quantities of garlic of the last campaign, both Spanish origin, both Argentine, so to sell old stocks, the price will decrease even at the expense of the product of the new crop. Easily it is expected a surplus of goods which can be marketed in the coming year, if well maintained in the fridge.
The new crops of South America (Figure 13) will be available before the end of the year. If the European market will not be able to absorb this product definitely not worth it to import it. Operators who in the last campaign imported garlic from Argentina have had to cope with major losses, so you have to wonder if it is worth to realize new imports.
Figure 13 Import of garlic from Argentina. The production of Italian garlic barely meets 20% of domestic needs. The bulk of consumption is met by garlic imported mainly from abroad, and particularly from China, Spain, Argentina and from third countries in the Mediterranean. At this time in the domestic market and is available only Argentine garlic, in small part, of the former Italian countryside, which had been preserved and the stocks of which, incidentally, are now being depleted.
In concluding this section on types of garlic imported must report on an abnormal form of commercialization of this important plant vegetable garden. The garlic import is subject to a customs duty of 9.5% and this has caused a boom in illegal trafficking to evade taxes giving rise to crime, which unfortunately is very profitable in the European Union. According to the European Anti-Fraud Office is the China (the main producer of garlic, with a global share of 80%), the country star of this black market, which is concentrated mainly in Great Britain, Italy and Poland. Therefore, it is desirable that the points of sale of this product will ensure the quality of fruit and vegetables, inviting will choose rigorously the Made in Italy (Figure 14).
Figure 14 Commercial kits and packages of Italian garlic (top and center) and workers who work on the industrial process (below).
The recommended values for the soil parameters, referring to the rhizosphere, for garlic cultivation are the follows:
- Weaving: should be fine and very fine so that the bulbs can develop fully and evenly;
- Drainage: the water must be removed from the soil readily without excess humidity, during the growing season, that can limiting the development of the garlic cultivation;
- Usable depth: the depth of the layers limiting the root systems should not be less than 40 cm, considering also that the growth of the roots of the garlic is done in a limited space;
- Total and active limestone: their value are generally irrelevant;
- pH: 6.5-7.5 , therefore, should be avoided acid and alcaline soils;
- Micronutrients : it is useful a good supply, especially of sulphur.
The recommended values for the climate parameters in the cultivation of garlic are as follows:
- Minimum temperature : -10 °C/-12 °C;
- Optimum temperature for germination: 26 °C;
- Optimum temperature for growth 15-25 °C;
- Maximum temperature: 30-35 °C;
- Humidity: the air humidity is not a problem. When it is high too, combined with dew, may cause the appearance of epigeal parasitic fungi.
The minimum interval between two successive cycles must not exceed 4 years. The crops are not recommended in the lawn and precession are those who keep pests such as sclerotinia garlic and nematodes.
It is recommended during the summer a plowing up to 40 cm combined with subsoiling in case there are problems of poor drainage.
It is recommended that the preparation of the seed bed, with harrows during the months of July-August for the summer-autumn sowing.
CHOICE OF TECHNIQUE OF PLANT
It is recommended that the choice of implant technique in relation to of the:
- Type of seeder;
- Propagation material;
- Plant spacing and density of investment.
It is recommended sowing manual which gives the best yield of production, even if, from the economic point of view, this technique, which allows a greater yield in the order of 13-14 quintals per hectare, it is not easy to implement for the increased need labor (Figure 15) . The "seeding" is performed by hand, using bulbils from bulbs healthy, free from rotting, of average weight above 2 g, disposed with the apex pointing upwards, at a depth of approximately 5 cm. The cloves are placed on small furrows previously performed with a rotary tiller equipped with a small furrow opener. II budding occurs at the expense of reserve substances and is more rapid when the cloves are large and at a temperature of 15-20 °C. For the investment of an hectare of garlic are needed q 6-7 of cloves in average. The planting distance can vary from 10 to 15 cm on the row and from 25 to 40 cm between rows, in relation to the mechanization of the farm.
Figure 15 - Manual "seeding" of cloves placed in the soil with the apex pointing upwards, at 5 cm depth.
For mechanical planting we recommend the use of the following machines:
- Semi-automatic drill-seeder: involves the use of five working units that they drop the cloves by adductor pipes in furrows which are then covered;
- Seeder automatic, pneumatic type, which distributes the cloves by controlled pressures, through adductor pipes, in furrows (figure 16).
It should also be emphasized that, while with the planting manual it is arranged in the in furrows where the cloves with the radical part facing downwards, with the seed, usually, the clove have randomly, mostly horizontally or sometimes inverted, with the so that, in the process of germination, the seedlings often have trouble getting the right position.
Figure 16 Mechanical pneumatic seed drills for sowing of garlic cloves. The use of these machines ensures uniformity of sowing and a considerable saving of manual labor. However, their use often causes a delay in the emergency, since the bulblli are placed, randomly, in different positions. However, this does not reduce the productive yield.
As propagation material we recommend the use of cloves obtained by shelling the bulbs. For the shelling, which must be done a few days before planting, we recommend the use of special equipment or handicraft of high precision. An essential element of this outfit is the heating of the cloves before shelling (which restricts problems microferite). Once shelled it is advisable to clean the cloves from the roots, outer tunics, cloves and bulbils external power to the bulb (teeth).
Normally the cloves are not permitted because the production is downgraded.
Disinfection of bulbils
Once the cloves have been cleaned up it is advisable to disinfect them with specific formulations to prevent it in the ground , especially if wet and very low temperatures , are infected by parasitic fungi ( Penicillium spp ) leading them to death. We recommend cleaning or disinfecting bath (Figure 16).
The planting pattern, the density of the investment and the depth of planting represent some important parameters to consider with the garlic planting. If the soil prepared for planting is very loose and dry before you start planting the garlic cloves is advisable to perform a soil roll to make it more compact and more leveled and accordingly apply the desired planting depth.
The particulars of the planting pattern and the depth of the plant are:
- Spacing between rows (cm): 30-33;
- Distance within the row (cm): 12-15;
- Distribution of plants (plants/ha): 250,000-270,000;
- Depth of planting (cm): 5-6. However, you have to specify that if the depth is less than cm 5-6, in the presence of winter frosts, the cloves can be pushed to the surface, while if it is higher, especially in clay soils, the seedlings may die of asphyxiation;
- Quantities of bulbs (q/ha): 7-8.
Nutritional requirements and mineral fertilization of garlic
The purpose of fertilization is ensure the availability to the garlic cultivation during the entire life cycle, the primary nutrients in amounts and in forms appropriate to the plant and in compliance with the quality requirements of the product and of the environment.
Nitrogen, in general, causes to an increase in the vigor of the plants with the early growth of the vegetative apparatus, a prerequisite for obtaining high production. An excessive availability of this element in the soil retards the bulb growth and at the end of the cycle delays the ripening of the bulbs and decreases its shelf life. With nitrogen deficiency, however, the leaves are growing much more slowly, developing a light green color and a more erect deportment, having a more rapid senescence and the formation of bulbs is accelerated.
The deficiency of phosphorus and potassium cause stunted growth, more rapid leaf senescence, delayed maturation and lateness of the harvesting, formation of bulbs with short appressed tunics, with a low dry residue and scarce life-shelf.
The availability of sulphur in the soil promotes the synthesis of sulphur compounds responsible for the characteristic flavor and aroma of the garlic, although it appears that the absorption of sulphur causes a depressive effect of ammonium ions and chlorine, which therefore tend to sweeten the bulbs.
Buyers indicative nutrients garlic (kg of nutrient per tonne of bulbs) are shown in Table 3.
| Table 3 - Requirements for principal nutrients of garlic cultivation (kg of nutrient per tonne of bulbs).
kg/t of bulbs
10,0 ÷ 11,0
3,0 ÷ 4,5
8,0 ÷ 10,0
2,5 ÷ 3,0
1,0 ÷ 5,0
0,1 ÷ 0,5
The rate of nutrient absorption is not uniform throughout the cycle of the crop, but varies with the different phenological stages. The demand for nitrogen is high especially during the vegetative stage of formation and emission of the leaves and then become very moderate during the bulb growth. In the final stage of the nitrogen cycle it is even harmful to the delay of ripening and for the reduction of shelf life of bulbs. Buyers of phosphorus and potassium, however, are particularly high in the phase of bulb magnification and increasing the sizes.
The knowledge of the physico-chemical characteristics of the soil is essential to establish an adequate program of fertilization and the need to verify whether or not fertilization enrichment. While the physical-mechanical analysis can be made only once, the chemical should be repeated at least every 3-4 years.
By inserting the fertilization of garlic in the balance of fertilization of the rotation, you have to take into account that the crop residues (leaf blades) represent more than 15% of dry matter, or are insignificant. Therefore, with reference to the requirements calculated for an expected production of 10 t/ha, equivalent to 110 kg/ha of N, 45 kg / ha of P2O5 and 90 kg/ha of K2O, these quantities of nutrients need to be considered all effectively removed from soil with bulbs.
Then it will be analyzed in more detail the fertilizer relative to the three macronutrients following a chronological order of application: first, phosphorus and potassium with the basic fertilization and after with the nitrogen fertilization in the vicinity of the plant and/or soil coverage.
In garlic organic fertilization is not recommended because it increases the sensitivity of the bulbs to different rot agents and causes disruption of nitrogen nutrition in the final phase of the cycle with delayed of ripening and deterioration of shelf life.
The dose to be administered should be determined on the basis of the allocation of available phosphorus in the soil. Therefore, it is necessary to perform the chemical analysis of the soil in order to measure, in the layer of soil affected by the roots of the garlic the amount (in ppm) of total phosphorus (P) and of assimilable phosphorus (P2O5) and then to perform an assessment agronomic about the quantitative level of nutrient useful for garlic plants. The levels are as follows, in view of the fact that the values expressed in ppm (parts per million), lower interval refers to sandy soils, loamy soils in the higher ones, to medium soils assume intermediate values:
Very low level of phosphorus (0÷6 ppm of P and 0÷15 ppm P2O5): the response to phosphate fertilization is certain for all crops. It is recommended fertilization enrichment, with doses ranging from 2 to 2.5 times the excise culture. Fertilization enrichment must continue until you reach the level of sufficiency for all crops in the rotation.
Low level (7 to 12 ppm P and 16 to 30 ppm P2O5): the response to phosphate fertilizer for all crops is likely. The fertilization is recommended that enrichment; doses to be made vary from 1.5 to 2 times the excise culture.
Intermediate level (13 to 20 ppm P and 31 to 45 ppm P2O5): the response to phosphate fertilization is less likely. It is recommended maintenance fertilization: they must be reinstated the excise culture with any increases (up to 1.5 times the excise) to account for the fraction of available phosphorus that, in almost all soils, undergoes retrograde to the presence of limestone or for pH <5.5.
High level (21 to 30 ppm P and 46 to 70 ppm P2O5): the response to phosphate fertilization is generally not likely, but it is suggested that a moderate intake of phosphorus for crops demanding for this item. The doses to be made to vary from 0.5 to 1 time the excise culture.
Very high level of phosphorus (>70 ppm P2O5): the response to phosphate fertilization is unlikely, therefore it is advisable not to administer the basics of phosphorus fertilizers.
The allocation of available phosphorus in the soil can be considered normal when it meets the needs of all crops in the rotation, starting with the most demanding. Considering the low mobility of this element, it is good to bury the entire dose would be working with the principal to bring in the layer of soil affected by the mass of roots. To accelerate the development of the root system and the initial growth of the crop, it is recommended to apply a starter fertilizer. Such fertilization is generally carried out with ammonium phosphate at a dose of about 50 kg/ha of phosphorus pentoxide, suitably localized below the seed and seedling.
The needs of the garlic for this element are averages and the maximum requirements on verify during the enlargement of the bulb.
The doses required are not high or low but medium and must be calculated, such as for the phosphorus, considering the allocation of land in exchangeable potassium and agronomic evaluation of the chemical analysis of the soil provides this envelope, in relation to the needs of the crop. The table shows the following levels of potassium, expressed in ppm and CEC (Cation-Exchange Capacity ) that is the amount of exchangeable cations, expressed in milliequivalents per 100 grams (meq/100g), that a material with adsorption properties may retain for ion exchange:
Very low level of potassium (0 ÷ 50 ppm of K and 0 to 60 ppm of K2O). The response to potassium fertilization is certain. It is recommended the enrichment fertilization with doses of 1.1 to 1.5 times the potassium removals from the garlic culture.
Low level (51 ÷ 100 ppm of K, 61 to 120 ppm of K2O, < 2% of CEC as K CEC % ). The response to potassium fertilization it is probable
for all crops. Fertilization recommended it is that of enrichment with doses ranging from 0.8 to 1.1 times the removals of the garlic culture.
Intermediate level (101 ÷ 150 ppm of K, 121 to 180 ppm of K2O, 2 % to 5 % CEC as K CEC %). The response to potassium fertilization is generally unlikely . The fertilization is recommended is that of maintenance doses of 0.5 to 0.8 times the removals of the culture.
High level ( 151 ÷ 200 ppm K, 181 to 240 ppm of K2O, > 5 % CEC as K CEC %). The response to potassium fertilization is not, in general, likely, so you should not fertilize. The potassium may be necessary for demanding crops and capable of high production , the dose should not exceed 0.5 times the the removals of the culture.
Very high (> 200 ppm K, > 240 ppm K2O). the response to the administration of potassium fertilizers is highly unlikely and, therefore, you should not fertilize.
Considering the low mobility of this element, it is good to bury the entire dose would be working with the principal to bring in the layer of soil affected by the mass of roots.
Nitrogen is the nutrient that most influences the production of garlic. The use of nitrogen fertilizers, however, unlike what happens with those phosphatic and potassic, requires particular attention, especially in determining the optimal dose to be administered, because incorrect interventions, both in defect is in excess, are paid in terms of loss of quantity and/or quality of the production.
In addition, the high degree of mobility in the soil of certain forms of nitrogen makes it necessary precautions to protect the environment (pollution of groundwater by nitrate nitrogen). The nitric form, finally, can accumulate in the tissues of plants, including edible parts, causing health risks to consumers. Nitrates, in fact, once ingested can be transformed into nitrite which, in turn, may combine with free amines and form nitrosamines, carcinogenic compounds. Garlic fortunately has a low tendency to accumulate nitrates in the bulb. Despite numerous studies on nitrogen balance in agriculture, we must say that is not easy to find a sufficiently simple and accurate method to determine the doses of nitrogen to be distributed to a culture.
The need for nitrogen fertilization can be calculated as the difference between the amount collected by the crop during the crop cycle and the amount of mineral nitrogen available in the soil at the beginning of the cycle more than that becomes available during the spring and summer, for mineralization humus and crop residues incorporated into the soil. In addition, one must consider that not all the nitrogen fertilizer is distributed absorbed by the plant, but depending on the type of soil, the climatic conditions, the formulation used (fertilizers, slow effect) and the mode of distribution (in all over the field, in bands, fertirrigation) the absorption efficiency of nitrogen fertilization may also vary widely so the dose technique made must be suitably increased. From the above it follows that:
Nitrogen is the nutrient that most affects the production of garlic. The use of nitrogen fertilizers, however, unlike what happens with those phosphatic and potassic , requires particular attention , especially in determining the optimal dose to be administered, since errors, both in the defect is in excess, are paid in terms of loss of quantity and / or quality of the production.
In addition, the high degree of mobility in the soil of certain forms of nitrogen makes it necessary precautions to protect the environment ( pollution of groundwater by nitrate nitrogen ) . The nitric, finally, can accumulate in the tissues of plants, including edible parts , causing health risks to consumers. Nitrates , in fact, once ingested can be transformed into nitrite which , in turn , may combine with free amines and form nitrosamines , carcinogenic compounds . Garlic fortunately has a low tendency to accumulate nitrates in the bulb . Despite numerous studies on nitrogen balance in agriculture , we must say that is not easy to find a sufficiently simple and accurate method to determine the doses of nitrogen to be distributed to a culture .
The need for nitrogen fertilization can be calculated as the difference between the amount collected by the crop during the crop cycle and the amount of mineral nitrogen available in the soil at the beginning of the cycle more than that becomes available during the spring and summer , for mineralization humus and crop residues incorporated into the soil. In addition, one must consider that not all the nitrogen fertilizer is distributed absorbed by the plant , but depending on the type of soil, the climatic conditions , the formulation used (eg fertilizers, slow effect ) and the mode of distribution ( in all over the field , in bands , fertigation ) the absorption efficiency of nitrogen fertilization may also vary widely so the dose technique made must be suitably increased. From the above it follows that:
Nitrogen fertilization = (taken N - available N) / Efficiency fertilization
It is been said that, for an expected production of 10 t/ha, the crop must have access to approximately 110 kg of nitrogen. In ordinary conditions, for example in the case where the preceding crop is represented by wheat, which is known to leave a reduced amount of residual nitrogen in the soil, and the organic matter content of the soil is relatively poor (1-1.3 %), is can therefore reasonable to estimate that the crop has available in the soil about 50-70 kg/ha of nitrogen for which the remaining 40-60 kg/ha should be made with fertilizing. If one considers that, because of the radical apparatus surface, the absorption efficiency of nitrogen fertilization with distributions all over the field is approximately 50%, it will be necessary to increase the dose up technique to make about 80-120 kg/ha of nitrogen.
Obviously, the dose to make changes if they change the terms of nitrogen balance:
Late cultivars were irrigated and growth, production requirements and higher.
Crop residues of precession may contain varying amounts of nitrogen, which may in part be available at the beginning of the cycle.
If it applied a starter fertilizer, the greater development of the root system increases the efficiency of nitrogen uptake.
Similarly, if the distribution of nitrogen fertilizer is localized in bands along the row the absorption efficiency increases.
In order to follow the rhythms of absorption of the crop, reducing the risk of leaching and to avoid an excess of nitrogen in the maturation phase of the bulbs, the intended dose of nitrogen should be fractionated into 3 times: 1/3 to the planting, 1/3 to the stage of 3-4 leaves, and 1/3 with at enlarged of the bulbs.
The most commonly used nitrogen fertilizers are ammonium sulphate plant (also to make sulfur) and ammonium nitrate or urea in coverage.
Finally, it should be noted that fertilization must be carried out exclusively with mineral fertilizers and not organic fertilizers because this last can cause plant root rot. Therefore, you should make a organic fertilizer to the previous crop garlic.
Water requirements and irrigation
In the early stages of growth the garlic do not need irrigation.
The satisfaction of crop water requirements is a key factor both in terms of quantity and quality of production.
Insufficient availability of water, in fact, entails a reduced growth, the increase of bulbs undersize and in summary lower production. On the contrary, an excess water is a waste of water, it causes the leaching of nutrients and phenomena of asphyxia of roots, promotes a greater susceptibility to pest attacks, and if it occurs in the final phase of the cycle, a retardation of ripening, a worsening of the shelf life of the bulbs and the qualitative characteristics such as lowering of the dry aroma and distinctive flavour, less "dressing" (tunics) of the bulbs.
In our growing environments, the rains that fall in autumn, winter and spring are generally sufficient to meet most of the water needs of the crop (which in our environments, it is estimated that on average in 1.500-2.500 m3/ha).
During the enlargement of the bulb, which occurs during the spring period (April-June ) may be required, depending on the growing environment and the seasonal trend, 2-3 irrigation interventions with individual volumes of irrigation intervals of about 400 m3/ha. Do not water in the vicinity of the harvest.
Research carried on garlic irrigation have shown that:
Water requirement = 425 mm.
No difference in yield between 100 and 125% ETc.
Significant difference below 100% ETc.
Peak Kc (Crop coefficient) = -1.3.
Data regarding the effects of different irrigation type on garlic cultivation they are reported in Table 4.
| Tabella 4 -
Means of soluble solids and bulb weight by irrigation system.
||Soluble Solids (%)
||100 Bulb Weight (kg)
||SE (bulb weight)
| Means not followed by the same letter are significantly different (p<0.5) by Tukeys multiple range test.
Market Yield, total weight, cull weight an soluble solids by irrigation level they are reported in Table 5.
| Table 5 -
Market yield, total weight, cull weight an soluble solids by irrigation level.
| *Significantly < 100% ETc by Dunnetts one tailed test (p<0.05).
Irrigation has been around for as long as humans have been cultivating plants. Man's first invention after he learned how to grow plants from seeds was probably a bucket. Ancient people must have been strong from having to haul buckets full of water to pour on their first plants. Pouring water on fields is still a common irrigation method today, but other, more efficient and mechanized methods are also used.
Early man would have used this "low-tech" method of irrigating crops. Collecting water in a bucket and pour it onto the fields. Today, this is still one of the most popular methods of crop irrigation. The system is called flood irrigation. Water is pumped or brought to the fields and is allowed to flow along the ground among the crops. This method is simple and cheap, and is widely used by societies in less developed parts of the world. The problem is, about one-half of the water used ends up not getting to the crops. Traditional flood irrigation can mean a lot of wasted water.
A large part, about 70%, of all the fresh water used in the world goes to irrigate crops. After use, much of this water cannot be reused because so much of it evaporates and transpires in the fields. If you consider that the majority of irrigation occurs where water is relatively scarce, you can see how important it is for farmers to find the most efficient methods of using their irrigation water.
Here are some things that farmers are doing to be more efficient:
For irrigating fruits and vegetables the drip irrigation method is much more efficient than flood irrigation. Water is sent through plastic pipes (with holes in them) that are either laid along the rows of crops or even buried along their rootlines. Evaporation is cut way down, and up to one-fourth of the water used is saved, as compared to flood irrigation.
- Leveling of fields: flood irrigation uses gravity to transport water, and, since water flows downhill, it will miss a part of the field that is on a hill, even a small hill. Farmers are using leveling equipment, some of which is guided by a laser beam, to scrape a field flat before planting. That allows water to flow evenly throughout the fields. (Actually, this method of levelling a field is also used to build flat tennis courts).
- Surge flooding: traditional flooding involved just releasing water onto a field. In using surge flooding, water is released at prearranged intervals, which reduces unwanted runoff.
- Capture and reuse of runoff: a large amount of flood-irrigation water is wasted because it runs off the edges and back of the fields. Farmers can capture the runoff in ponds and pump it back up to the front of the field where it is reused for the next cycle of irrigation.
Spray irrigation is a more modern way of irrigating, but it also requires machinery. This system is similar to the way you might water your lawn at home - stand there with a hose and spray the water out in all directions. Large scale spray irrigation systems are in use on large farms today. These systems have a long tube fixed at one end to the water source, such as a well. Water flows through the tube and is shot out by a system of spray-guns.
A common type of spray-irrigation system are the center-pivot systems. They work in the same way you might water your yard. If you placed a faucet in the center of your yard, you could take a hose, punch holes all along it, and attach a spray gun at the end. Turn the water on, pull it tight, and start spraying (water is also spraying from the holes in the hose at the same time). While you are spraying you are also walking around in a circle (with the faucet at the center of the circle). Using this method you can get a very large circle of lawn watered with just a short hose.
The center-pivot systems have a number of metal frames (on rolling wheels) that hold the water tube out into the fields. And there can be a very big water gun at the end of the tube. Electric motors move each frame in a big circle around the field (the tube is fixed at the water source at the center of the circle), squirting water.
If you've been in an airplane you can easily locate center-pivot irrigation systems on the ground. You can't miss them, just look for green circles of irrigated land below.
Better spray irrigation is by use of traditional spray irrigation, water basically is just shot through the air onto fields. In the dry and windy air, a lot of the water sprayed evaporates or blows away before it hits the ground. Another method, where water is gently sprayed from a hanging pipe uses water more efficiently. This method increases irrigation efficiency from about 60% (traditional spray irrigation) to over 90 percent. Plus, less electricity is needed.
Hoeing and Weed Control
Hoeing is best done when the weeds are very small seedlings or newly emerged shoots of perennial weeds. This allows shallow hoeing to kill the weeds without bringing new seeds to the soil surface. Shallow hoeing also reduces root damage to the crop. Stirrup hoes (shuffle hoes) are ideal for shallow weeding. A garden rake moved in an oval motion covers large areas. Traditional chopping type hoes are sometimes useful for hacking back weeds in untilled corners of the garden, but in loose soil they tend to dig too deep, damage crop roots and bring up more weed seeds. If the weeds are so large that a traditional hoe is needed, hand pulling or digging them out may be more efficient in the long run.
One objective of hoeing should be the creation of a dust mulch. This is a layer of very loose soil crumbs, typically 0.5 to 1.5 inches thick. It can be achieved with most tools that work the soil shallowly including a rake, garden claw or stirrup hoe. Weeds seeds need good contact with the soil for germination just like crop seeds. Since most individuals of most annual weed species emerge from the top inch of soil, maintenance of a dust mulch greatly decreases weed density. Obviously, a dust mulch is impossible to maintain during wet weather, but when it is feasible, a dust mulch is a highly effective weed management technique.
Hoeing is best done when the soil is slightly dry and the weather is warm and sunny. First, such conditions are ideal for drying out uprooted weeds and producing a dust mulch. Second, the hoeing will do less damage to soil structure under such conditions than when the soil is wet. Third, hoeing in rainy, or foggy conditions is likely to spread disease, both on your clothing and by bringing soil into contact with crop foliage.
The performance of mechanical weeding in the alleyways can be useful in the early stages of development on the ground with a tendency to form crust and when you want to eliminate weeds at different times of the growing cycle. The weeding in the intermediate and final stages of the cycle, however, frequently damaging the already reduced and shallow root system, and sometimes are too risky for the integrity of the bulbs. With the weeding should avoid reporting the ground in the vicinity of the bulb, but rather to leave slightly the base of the plant, especially in humid years, so as to reduce the incidence of rots.
The mechanical control of weeds is done with hoeing surface, performed with small tillers, not to cause damage to root, very shallow.
Often weeding are integrated with the chemical weeding in post-emergence, with Oxyfluorfen or Setoxydim to the stage of 3-4 leaves.
The weeding, as well as removing weeds, serve to reduce the loss of water by evaporation and then to keep the water reserves are very useful in the phase of enlargement of the bulbs, when you have the greatest demand for water.
Therefore, under dry and low rainfall, especially during the spring, the weeding assume greater importance for which the chemical weed control, although less expensive than machining, it can not completely replace the need to reduce water losses. In the event that the company has availability irrigation can be performed in an emergency irrigation phase of enlargement of the bulb (April-May), especially in dry years.
In May you manually delete the floral scapes when they reach an inch in length, to facilitate the enlargement of the bulbs, since the beginning of the production ceases vegetative activity. The elimination of floral scapes is also required for the packaging of garlic in braids, while for packaging nets seems that the presence of the flowering stem makes it easier to keep the garlic.
Very important is the control of perennial weeds. Many perennial weeds have deep storage roots or rhizomes that resprout after the tops are cut or pulled (e.g., hedge bindweed, Canada thistle. etc.). Since the storage roots or rhizomes are too deep in the soil to damage with normal spading or rototilling, your best hope for organically controlling these weeds is to exhaust the storage organs by repeated removal of top growth. Generally, the net flow of nutrients is from the root until formation of the third or fourth leaf, so time your removals accordingly. Typically, eradication of deep-rooted perennials requires about 6-8 well-timed weedings the first year followed 3-5 the second.
Integrated control of weeds garlic is summarized in Table 6.
| Table 6 - Summary information on the integrated control of weeds of the garlic cultivations.
||Active principle (a.p.)
||% di a.p.
||L/ha or Kg/ha
|Winter Graminaceae and
Quizalofop-ethyl isomer D
Glyphosate (N-(phosphonomethyl)glycine) is a broad-spectrum systemic herbicide used to kill weeds, especially annual broadleaf weeds and grasses known to compete with commercial crops grown around the globe. It was discovered to be a herbicide by Monsanto chemist John E. Franz in 1970. Monsanto brought it to market in the 1970s under the trade name "Roundup", and Monsanto's last commercially relevant United States patent expired in 2000.
Glyphosate was quickly adopted by farmers, even more so when Monsanto introduced glyphosate-resistant crops, enabling farmers to kill weeds without killing their crops. In 2007 glyphosate was the most used herbicide in the United States agricultural sector, with 180 to 185 million pounds (82,000 to 84,000 tonnes) applied, and the second most used in home and garden market where users applied 5 to 8 million pounds (2,300 to 3,600 tonnes); additionally industry, commerce and government applied 13 to 15 million pounds (5,900 to 6,800 tonnes). With its heavy use in agriculture, weed resistance to glyphosate is a growing problem. While glyphosate and formulations such as Roundup have been approved by regulatory bodies worldwide and are widely used, concerns about their effects on humans and the environment persist.
Glyphosate's mode of action is to inhibit an enzyme involved in the synthesis of the aromatic amino acids tyrosine, tryptophan and phenylalanine. It is absorbed through foliage and translocated to growing points. Because of this mode of action, it is only effective on actively growing plants; it is not effective as a pre-emergence herbicide.
Some crops have been genetically engineered to be resistant to glyphosate (i.e., "Roundup Ready", also created by Monsanto Company). Such crops allow farmers to use glyphosate as a post-emergence herbicide against both broadleaf and cereal weeds, but the development of similar resistance in some weed species is emerging as a costly problem. Soy was the first "Roundup Ready" crop.
Glyphosate is an aminophosphonic analogue of the natural amino acid glycine, and the name is a contraction of gly(cine) phos(phon)ate. The molecule has several dissociable hydrogens, especially the first hydrogen of the phosphate group. The molecule tends to exist as a zwitterion where a phosphonic hydrogen dissociates and joins the amine group. Glyphosate is soluble in water to 12 g/L at room temperature. Main deactivation path is hydrolysis to aminomethylphosphonic acid (AMPA).
Glyphosate kills plants by interfering with the synthesis of the aromatic amino acids phenylalanine, tyrosine and tryptophan. It does this by inhibiting the enzyme 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS), which catalyzes the reaction of shikimate-3-phosphate (S3P) and phosphoenolpyruvate to form 5-enolpyruvyl-shikimate-3-phosphate (ESP). ESP is subsequently dephosphorylated to chorismate, an essential precursor for the amino acids mentioned above. These amino acids are used in protein synthesis and to produce secondary metabolites such as folates, ubiquinones and naphthoquinone. X-ray crystallographic studies of glyphosate and EPSPS show that glyphosate functions by occupying the binding site of the phosphoenolpyruvate, mimicking an intermediate state of the ternary enzyme substrates complex. The commercially important enzyme that glyphosate inhibits, EPSPS, is found only in plants and micro-organisms. EPSPS is not present in animals, which instead obtain aromatic amino acids from their diet. However, glyphosate has also been shown to inhibit other plant enzymes, and also has been found to affect animal enzymes. Glyphosate is absorbed through foliage. Because of this mode of action, it is only effective on actively growing plants; it is not effective in preventing seeds from germinating.
About environmetal problems, glyphosate adsorbs strongly to soil and is not expected to move vertically below the six inch soil layer; residues are expected to be immobile in soil. Glyphosate is readily degraded by soil microbes to AMPA and carbon dioxide. Glyphosate and AMPA are not likely to move to ground water due to their strong adsorptive characteristics. However, glyphosate does have the potential to contaminate surface waters due to its aquatic use patterns and through erosion, as it adsorbs to soil particles suspended in runoff. If glyphosate reached surface water, it would not be broken down readily by water or sunlight. The median half-life of glyphosate in soil ranges between 2 and 197 days; a typical field half-life of 47 days has been suggested. Soil and climate conditions affect glyphosate's persistence in soil. The median half-life of glyphosate in water varies from a few days to 91 days. According to the National Pesticide Information Center fact sheet, Glyphosate is not included in compounds tested for by the Food and Drug Administration's Pesticide Residue Monitoring Program, nor in the United States Department of Agriculture's Pesticide Data Program, however a field test showed that lettuce, carrots, and barley contained glyphosate residues up to one year after the soil was treated with 3.71 pounds of glyphosate per acre.
Glyphosate is effective in killing a wide variety of plants, including grasses, broadleaf, and woody plants. It has a relatively small effect on some clover species. By volume, it is one of the most widely used herbicides. It is commonly used for agriculture, horticulture, viticulture and silviculture purposes, as well as garden maintenance (including home use). Prior to harvest glyphosate is used for crop desiccation (siccation) to increase the harvest yield.
In many cities, glyphosate is sprayed along the sidewalks and streets, as well as crevices in between pavement where weeds often grow. However, up to 24% of glyphosate applied to hard surfaces can be run off by water. Glyphosate contamination of surface water is highly attributed to urban
Glyphosate is one of a number of herbicides used by the United States and Colombian governments to spray coca fields through Plan Colombia. Its effects on legal crops and effectiveness in fighting the war on drugs have been disputed. There are reports that widespread application of glyphosate in attempts to destroy coca crops in South America have resulted in the development of glyphosate-resistant strains of coca nicknamed "Boliviana Negra", which have been selectively bred to be both "Roundup Ready" and larger and higher yielding than the original strains of the plant.However, there are no reports of glyphosate-resistant coca in the peer-reviewed literature. In addition, since spraying of herbicides is not permitted in Colombian national parks, this has encouraged coca growers to move into park areas, cutting down the natural vegetation, and establishing coca plantations within park lands.
Glyphosate is the active ingredient in herbicide formulations containing it. However, in addition to glyphosate salts, commercial formulations of glyphosate contain additives such as surfactants which vary in nature and concentration. Laboratory toxicology studies have suggested that other ingredients in combination with glyphosate may have greater toxicity than glyphosate alone. Toxicologists have studied glyphosate alone, additives alone, and formulations. Glyphosate has a United States Environmental Protection Agency (EPA) Toxicity Class of III (on a I to IV scale, where IV is least dangerous) for oral and inhalation exposure. Thus, as with other herbicides, the EPA requires that products containing glyphosate carry a label that warns against oral intake, mandates the use of protective clothing, and instructs users not to re-enter treated fields for at least 4 hours. Glyphosate does not bioaccumulate in animals; it is excreted in urine and faeces. It breaks down variably quickly depending on the particular environment. Human acute toxicity is dose related. Acute fatal toxicity has been reported in deliberate overdose. Epidemiological studies have not found associations between long term low level exposure to glyphosate and any disease.
The EPA considers glyphosate to be noncarcinogenic and relatively low in dermal and oral acute toxicity. The EPA considered a "worst case" dietary risk model of an individual eating a lifetime of food derived entirely from glyphosate-sprayed fields with residues at their maximum levels. This model indicated that no adverse health effects would be expected under such conditions.
Glyphosate is present in human urine samples from 18 European countries. Malta showed the highest test results with the chemical showing up in 90% of samples and the average for all countries was 43.9%. Diet was stated as the main source.
The European Commission's review of the data conducted in 2002 concluded that there was equivocal evidence of a relationship between glyphosate exposure during pregnancy and cardiovascular malformations; however, a review published in 2013 found that the evidence "fails to support a potential risk for increased cardiovascular defects as a result of glyphosate exposure during pregnancy
Health, environmental and food chain effects from alteration of gut flora by wide use of glyphosate are largely unexplored.
Glufosinate or its ammonium salt DL-phosphinothricin is an active ingredient in several nonselective systemic herbicides such as Basta, Rely, Finale, Ignite, Challenge, and Liberty. It interferes with the biosynthetic pathway of the amino acid glutamine and with ammonia detoxification. It has been used in pre-harvest crop desiccation. Some plants have been genetically modified for resistance to glufosinate. The gene which gives resistance to glufosinate is a bar or pat gene which was first isolated from two species of Streptomyces bacteria. There are glufosinate-resistant transgenic varieties of several crops, including cotton, canola, corn, soybean, sugarbeet, and rice. Of these, canola, cotton, soybean and maize are currently on the market. This includes Bayer's LibertyLink genes, used in over 100 hybrids.
Glufosinate was found to be toxic to reproduction and was included in a biocide ban proposed by the Swedish Chemicals Agency and approved by the European Parliament on January 13, 2009.Phosphinothricin is an glutamine synthetase inhibitor that binds to the glutamate site. Glufosinate-treated plants die due to a buildup of ammonia and corresponding decrease in pH in the thylakoid lumen, leading to the uncoupling of photophosphorylation. The uncoupling of photophosphorylation causes the production of reactive oxygen species, lipid peroxidation, and membrane destruction.
Pendimethalin protects crops like wheat, corn, soybeans potatoes, cabbage, peas, carrots and asparagus. It is used to control annual grasses and certain broadleaf weeds which interfere with growth, development, yield and quality of agricultural and horticultural crops by competing on nutrients, water and light.
In areas where weed infestation is particularly high, yield losses can render wheat production economically unviable. In addition to wheat, a large number of crops are grown in Europe that are a relatively small percentage of total agricultural output. Herbicide options are limited for these minor crops, with few effective herbicides available in the vegetable sector. Long-term field studies performed in Germany by governmental research and advisory institutes together with farmers rank Pendimethalin as an efficient herbicide to control blackgrass, regarding to weed control efficacy, crop yield, treatment costs and environmental impact. Pendimethalin acts both pre-emergence, that is before weed seedlings have emerged, and early post-emergence. Pendimethalin inhibits root and shoot growth. It controls the weed population and prevents weeds from emerging, particularly during the crucial development phase of the crop. Its primary mode of action is to prevent plant cell division and elongation in susceptible species. In the HRAC classification of herbicides according their mode of action, pendimethalin is listed in group K1. Herbicide resistance typically increases production costs and limits options for herbicide selection, cultivations and rotations. Up to now Pendimethalin does not show resistance. It is not cross-resistant with other grass weed herbicides. This means that Pendimethalin supports the effects of other supplementary grass weed herbicides that use a different mode of action. Pendimethalin is registered globally for a wide range of crops, according to human and environmental safety standards by the European Commission, US-EPA, Canada-PMRA, Japan, Brazil-ANVISA and others.
Metazachlor is a residual herbicide used to control broad leaved weeds and annual grasses. It is a synthetic compound and a member of the chloroacetamide chemical family. It was first manufactured by BASF as an herbicide and is now commonly used on its own and in combination with other plant protection products, such as clomazone and quinmerac. Metazachlor is applied directly to the soil and is not suitable as an aerial spray. It can be applied to all soil types expect sand, very light soils and soils containing more than 10% organic material. The compound is absorbed through the roots of the target weeds to the growing points of the plant. Here it inhibits VLCFAs, thereby inhibiting cell division. Metazachlor can be applied to sown oilseed rape, vegetable crops such as brassicas, like Brussels sprouts, cauliflowers, cabbage, broccoli and calabrese as well turnips and Swedes. It can also be used on ornamentals, nursery stock, in forestry and on wood land.
Oxyfluorfen is a member of the diphenyl ether group of herbicides. 4Farmers Oxyfluorfen 240 EC Herbicide has the inhibitor of
protoporphyrinogen oxidase mode of action. For weed resistance management Oxyfluorfen 240 EC Herbicide is a Group G herbicide. Some naturally
occurring weed biotypes resistant to Oxyfluorfen may exist through normal genetic variability in any weed
population. The resistant individuals can eventually dominate the weed population
if these herbicides are used repeatedly. These resistant weeds will not be controlled by Oxyfluorfen.
Since the occurrence of resistant weeds is difficult to detect prior to use, 4Farmers
Pty Limited accepts no liability for any losses that may result from the failure of
Oxyfluorfen to control resistant weeds. For optimum residual weed control, Oxyfluorfen
should be applied to the soil surface prior to weed emergence after all other
agricultural operations have been completed, such as mechanical cultivation and
reshaping of irrigation furrows. The area should be left undisturbed during the
period of desired weed control. When applied to seedling weeds, they should be
young and actively growing. Weed control for up to 6 months is expected but spot
treatment, with knockdown herbicides, for escape weeds and perennial grassemay be necessary.Spray equipment should be calibrated before use. Oxyfluorfen should be applied uniformly as a directed treatment to the base of tree
and vine crops using flat fan or off-centre nozzles. Complete coverage of seedling
weeds is required for maximum knockdown effect. A water volume of 250 to 500
litres per hectare is recommended for treatments of bare soil. A spray volume of
100 to 1,350 litres per hectare is recommended where seedling weeds (4 to 6 leaf)
are present. Ensure both the weed foliage and the soil surface are sprayed. Use
higher volumes for high weed density. Tank mixtures of 75mL/ha of Oxyfluorfen with
Glyphosate 450 or Glyphosate 360 herbicides should be applied in 30 to 200 litresspray volume per hectare. For maximum residual control Oxyfluorfen should not be incorporated or disturbed after application.
Ioxynil: main names are Totril, Preskil . It is efficient against broad leaf weeds at rates of about 500 g.a.i/ha. However, it may be marginally selective and may be used in repeated applications at lower rates, such as 100 to 200 g a.i./ha. Mixtures of bromoxynil and ioxynil exist on the market (Oxytril) : extreme care should be taken in using these mixtures. Use rates that will bring a maximum of 100 g.a.i. bromoxynil per ha in repeated applications (2 or 3 applications with one week interval).
Quizalofop-ethyl isomer D : known as Targa D, Pilot or Assure, it is efficient against grasses at rates between 60 g.a.i/ha (annuals) and 150 g.a.i/ha(perennials). It should be applied after 3 leaves until tillage (grasses). The addition of oil or surfactant is highly recommended (type Agral).
Propaquizafop is a synthetic compound of the chemical family the aryloxyphenoxypropionate. Propaquizafop acts as a systemic herbicide of annual and perennial grasses. It is applied as a foliar spray and, being quickly absorbed through the leaves and translocated to the meristematic growing regions of the plants, where it inhibits cell growth and division through the inhibition of ACCase inhibition. Propaquizafop can be used on a wide range of broad-leaved crops, including sugarbeet, oilseed rape, soybeans, sunflower, other field crops, vegetables, fruit trees, vineyards and forestry.
It is important to note that a non chemical control is possible at Pre-emergence weed control. We recommend the use of machines which perfectly controls the working depth and performs a shallow cultivation that will avoid bringing deep weeds into the top soil layer. It will also facilitate an even weed emergence.
When soil preparation is necessary, we try to work the soil as shallow as possible. Because of an excellent working depth control it can finetune the soil preparation, incorporate the residues in the top soil layer or make the right finish. It will also avoid bringing deep weeds in the top layer (essential for non-competitive crops such as onion, garlic) and facilitate an even weed emergence (easier to destroy).
It may be fitted either with disks placed up front or ripper tines with the levelling cross board system. When a large amount of crop residues has to be handled, a front straw harrow may be fitted in front of the discs. In some cases we might recommend the use of a shallow cultivation tool in combination with the seeder automatic machines.
Pulling weeds is a last resort when other methods of management have failed, or when a few escapes need to be removed to prevent seed production. For some small seeded, slow establishing crops like carrots or parsnips that do not transplant well, hand pulling is sometimes necessary to remove small weeds from around the young crop. In the latter case, the amount of hand weeding can be reduced by sowing slow emerging crops in relatively weed free areas of the garden and preceding planting with a short period of clean fallow to reduce weed density.
The best technique for pulling weeds depends on the type of weed and the situation. Small weeds are easiest to pull when the soil is wet (i.e., too wet for tillage). Keeping your weight off of the soil at such times is critical, however, to avoid destroying soil structure (Stay of soil). To pull small weeds from among small, fragile crop plants like young carrots, place a finger on the ground on both sides of the weed and pull with the other hand. This holds the soil in place, and prevents uprooting the crop along with the weed.
Species with strong taproots are also easiest to pull when the soil is wet, but again, care should be taken to avoid trampling the soil. Also, the crop should be dry to avoid spreading disease. Grasp the weed by the top of the taproot rather than by the stem or foliage. Then slowly pull straight up with a slight twisting motion. This will break the feeder roots free from the taproot and allow the taproot to be pulled up whole. A jerking pull will tend to break the root. Removing most of the root is critical since the plant will resprout from dormant buds in any large pieces that remain in the soil. The resulting complex root system will be impossible to pull and you will have to dig to remove it. Maintaining a high state of tilth is critical for hand pulling weeds with taproots (Tilth & weeding). If the soil is moist, loose and has a good crumb structure, even large dandelions can be pulled whole. If the soil is not in good condition or is not wet enough or the weed is really large, an asparagus knife, long trowel or narrow spading fork may be needed to get the whole root. If the plant is so large that you have to hand pull it, it may reroot if the soil is moist or rain is expected. Also, if the plant is flowering, it may make seeds even after you uproot it. Consequently, carrying along a couple of 5 gallon buckets to use for removing the weeds from the garden may help reduce subsequent weeding. Weeds that are unlikely to set seeds can be left on a hard surface like concrete or boards until thoroughly dead and then composted.
Fibrous rooted species like annual grasses and plantains are easiest to pull when the soil is starting to dry. If the soil is dry and hard, the shoot will tend to break off, leaving the root system to resprout, whereas if the soil is moist, a lot of soil will cling to the roots. If the soil is moderately dry, hitting the root crown against any hard object will knock most of the soil off the roots. This will decrease likelihood of the weed rerooting if it is left on the ground and avoid exporting your precious topsoil if it is removed from the garden.
If a few weeds with spreading rhizomes or root systems are encroaching from the edge of the garden, pulling the shoots is more effective than hoeing. Hoeing cuts the shoots near the surface whereas pulling the shoot usually brings up a long white underground shoot. This depletes the underground root-rhizome system more quickly than hoeing. Canada thistle is one such species. Since the base and underground portion of the shoot is free of thorns, the plant can be pulled from this point without heavy gloves.
Harvesting of the garlic
Physiological maturity is manifested by the presence of yellow leaves and dried. Garlic is generally ready for harvest when the leaves are yellow or dried in their
upper third and start to bend on the ground. If the harvest get too early tunics are bad
dried, while if the harvest is delaied the bulbs are often invaded by saprophytic organisms that confer them a blackish colour.
The harvest for fresh starts from April to May, while that for the product for storage in plaits or grappes from June (Southern Italy) to August (Northern Italy) . If the garlic is prematurely harvested the product destinated to storage is undergoes to rapid dehydration.
The harvest is commonly done by machine. But especially in southern Italy, the machines are not much used and this for the farm pulverization and because the farm sizes are too small
and for the individualistic causes of the farmers and for different needs related to the type of business and the marketing methods.
They are available the facilitator machines and the integral harvester machines.
Facilitator machines for the garlic harvest
They are divided into two main groups:
Integral harvesting machines
- machines that operate only by the extraction of plants from the soil with blades that dig the bulbs and rotary harrows suitably modified.
The blades operate the cutting of the roots below the bulb at 10 cm depth of about and then raise the plant; do not require that the crop is planted in the rows, but operate on a working width of 1.8 m. Their work capacity is about 0.55 ha/h.
This modified rotary harrows work at a depth of about 10 cm without to damage the bulbs and have the advantage to crushing the clods of earth raised together with the plants, in the soil sufficiently dry; usually operate in 5 culture rows with a working capacity of about 0.35 ha/h.
- windrow grubbing machines that operate by making:
- The cutting of the roots,
- The excavation of the bulbs by small plowshares,
- Soil separation,
- Preparation of the cultivation field in windrows.
The machin work on 3-4-5 files at once with a working capacity of 0.3 ha/h .
After the plants were uprooted, placed in windrows and left to dry for a few days, they are subjected to root cleaning, packing in bundles (20-30 plants) or braids (about 20 bulbs per 1 kg of weight), loading and transport to the central building or storage.
To make the harvest, the field in windrows, the cleaning, tying in bunches or plaits, loading and transport are being used total labor force of about 150 hour per man and per hectare.
They are dig-harvesing-tying single row, trained by tractor. The harvesting head (lateral or rear) is constituted of a excavation plowshare, a shaking device for the separation of soil from plants and by a device that holds the plants for the leaf apparatus. The plants are
then accompanied to a device binder that binds the plants in bundles of 30-40 plants and their deposition on the ground. These machines operate on a single row and have a working capacity very limited (from 0.9 up to 0.12 ha/hour) but completely eliminate the subsequent phases of cleaning and packaging. The harvesting, cleaning of decks, loading and transportation account for about
In our campaigns, drying, cleaning and packaging of garlic from storage are traditionally carried out in the field for which the use of harvesting grains seems primarily intended for garlic for fresh consumption. The average production of garlic are of the order of 10-12 t/ha in a white bulb types and 7-8 t/ha in the red ones. The production of tip frequently reach 20 t/ha.
Follow the exposure of some machines used for the harvest of the garlic (figures 17, 18, 19 and 20):
Figure 17 - 1-row garlic harvester-binder. Lifting is done by a blade which passes under the garlic bulbs and by two belts which pull up the garlic by the leaves. The garlic is carried by the belts, passing through a vibrator, to an automatic bundle binding system. The bundles of garlic are then removed by a conveyor belt. The machine is operated by one person. Lateral movement is ensured hydraulically.
The machine has setting systems allowing it to be adapted to various types of planting.
Sideways movement of the machine to align it on the row to be harvested, share depth, height of the lifting belts, binding height, string tension, bundle size adjustment.
The characteristics are: 1-row per machine; carried by 1 person; distance between rows: 40 cm minimum; nominal speed: 4 km/h; tractor power: 50 hp; sideways movement between rows: 130 cm.
The technique characteristics are: a mass of 800 kg; the length of 3.400 mm; the wide 2.100 mm; height 1.600 mm.
Figure 18 - 2-row garlic harvester-binder. Similar to the previous described. The machine is carried by two people. The operating characteristics are: machine 2 rows; minimum distance between rows 43 cm; maximum distance between rows 55 cm; speed 4 km/h; tractor power 70 hp; lateral displacement between rows: 130 cm; mass 1,430 kg; length 3,400 mm, width 2,000 mm, height 2,000 mm.
Figure 19 - Harvester sharp. Similar to the previous described. The machine is run by two people. The main operating characteristics are: machine 2 rows; minimum distance between rows 43 cm; maximum distance between rows 55 cm; speed 4 km/h; tractor power 70 hp; lateral displacement between rows 70 cm; mass 1,280 kg; length 4,100 mm, width 2,750-3,500 mm, height 2,450 mm.
Figure 20 - 3 or 4 or 5 row garlic harvester-topper SAC.wmv. Double chassis, towed machine. It is hydraulically powered by pumps which are driven by the tractor's power take-off. The lifting system is identical and independent for each row. The bulb is lifted by a blade and the leaves are grabbed between two belts. The garlic is carried to the topping system after passing through a vibrator. A second set of belts levels off all the bulbs and two disks cut the leaves. A conveyor belt carries the bulbs to one side of the machine. After being cut, the leaves fall on to the ground behind the machine.
The machine is operated by one person, and it has setting systems allowing it to be adapted to various types of planting. Lateral guidance is hydraulically controlled. technical characteristics: 3-, 4- or 5-row machine; minimum setting between rows 43 cm; maximum setting between rows 50 cm; nominal speed 3 km/h; tractor power 70 hp; lateral displacement between rows 70 cm; mass 2,400, 2,800, and 3,400 kg; length (fixed) 4,700 mm; width 2,000, 2,200, and 3,500 mm, depending from row number (3,4 or 5 rows); height (fixed) 2,300 mm.
After being extirpated the garlc must undergo a natural drying that can occur in the open field or farmyard. The finished product must be marketed between July 30 and 31 May of the following year. The drying can also be forced, when air produced by a fan is forced through a grid, some times even heated (depending on air humidity), or through dedicated boxes with grids where fresh garlic was placed.
Garlic has a high energy value (140 cal per 100 g of the edible part) and a high content of potassium, iodine, zinc, manganese, vitamin B.
The dry matter content of garlic is generally high and can vary, according to the cultivar from 30 to 56%.
The bulb is almost devoid of starch, but it accumulates carbohydrates, under form of fructans (long-chain polymer of fructose).
A protein content of 4-6% is commonly low according with the high content of dry matter, while it is very low in fat even if it contains, an essential oil rich in sulphur compounds (0.1-0.25%). The characteristic odour and flavour are conferred by some volatile sulphur compounds (mainly allicin) that are formed from some precursor odourless and non-volatile (alliin) of the bulb when the plant tissues are damaged (cut, crushed).
Allicin features the thiosulphinate functional group, R-S(O)-S-R. The compound is not present in garlic unless tissue damage occurs, and is formed by the action of the enzyme alliinase on alliin. Allicin is chiral but occurs naturally only as a racemate. The racemic form can also be generated by oxidation of diallyl disulphide:
(SCH2CH=CH2)2 + RCO3H → CH2=CHCH2S(O)SCH2CH=CH2 + RCO2H
Alliinase is irreversibly deactivated below pH 3; as such, allicin is generally not produced in the body from the consumption of fresh or powdered garlic. Furthermore, allicin can be unstable, breaking down within 16 h at 23 °C.
Several animal studies published between 1995 and 2005 indicate that allicin may reduce atherosclerosis and fat deposition, normalize the lipoprotein balance, decrease blood pressure, have anti-thrombotic and anti-inflammatory activities, and function as an antioxidant to some extent. Other animal studies have shown a strong oxidative effect in the gut that can damage intestinal cells, though many of these results were obtained by excessive amounts of allicin, which has been clearly shown to have some toxicity at high amounts, or by physically injecting the lumen itself with allicin, which may not be indicative of what would happen via oral ingestion of allicin or garlic supplements. A randomized clinical trial funded by the National Institutes of Health (NIH) in the United States and published in the Archives of Internal Medicine in 2007 found that the consumption of garlic in any form did not reduce blood cholesterol levels in patients with moderately high baseline cholesterol levels. The fresh garlic used in this study contained substantial levels of allicin, so the study casts doubt on the ability of allicin when taken orally to reduce blood cholesterol levels in human subjects.
In 2009, Vaidya, Ingold and Pratt clarified the mechanism of the antioxidant activity of garlic, such as trapping damaging free radicals. When allicin decomposes, it forms 2-propenesulfenic acid, and this compound is what binds to the free-radicals. The 2-propenesulfenic formed when garlic is cut or crushed has a lifetime of less than one second.
Allicin has been found to have numerous antimicrobial properties, and has been studied in relation to both its effects and its biochemical interactions. One potential application is in the treatment of methicillin-resistant Staphylococcus aureus (MRSA), an increasingly prevalent concern in hospitals. A screening of allicin against 30 strains of MRSA found high level of antimicrobial activity, including against strains that are resistant to other chemical agents. Of the strains tested, 88% had minimum inhibitory concentrations for allicin liquids of 16 mg/L, and all strains were inhibited at 32 mg/L. Furthermore, 88% of clinical isolates had minimum bactericidal concentrations of 128 mg/L, and all were killed at 256 mg/L. Of these strains, 82% showed intermediate or full resistance to mupirocin. This same study examined use of an aqueous cream of allicin, and found it somewhat less effective than allicin liquid. At 500 mg/L, however, the cream was still active against all the organisms testedwhich compares well with the 20 g/L mupirocin currently used for topical application.
A water-based formulation of purified allicin was found to be more chemically stable than other preparations of garlic extracts. They proposed that the stability may be due to the hydrogen bonding of water to the reactive oxygen atom in allicin and also to the absence of other components in crushed garlic that destabilize the molecule.
Although there are preliminary studies indicating some potential benefit of garlic in treating the common cold, a 2012 report in the Cochrane Database of Systematic Reviews concluded that "there is insufficient clinical trial evidence regarding the effects of garlic in preventing or treating the common cold. A single trial - The trial that relied on self reported episodes of the common cold but was of reasonable quality in terms of randomisation and allocation concealment, suggested that garlic may prevent occurrences of the common cold but more studies are needed to validate this finding. Claims of effectiveness appear to rely largely on poor-quality evidence". Similar conclusions are voiced in a 2013 report, which states "Garlic as a preventative or treatment option for the common cold" and still "could not be recommended, as only one relatively small trial evaluated the effects separately. Garlic might be effective in some areas of clinical practice, but the evidence levels were low, so further researches should be well designed using rigorous method to avoid potential biases".
Alliin is a sulfoxide that is a natural constituent of fresh garlic. The formula is (IUPAC name) (2R)-2-amino-3-[(S)-prop-2-enylsulfinyl]propanoic acid. It is a derivative of the sulphurate amino acid named cysteine. When fresh garlic is chopped or crushed, the enzyme alliinase converts alliin into allicin, which is responsible for the aroma of fresh garlic. Garlic has been used since antiquity as a therapeutic remedy for certain conditions now associated with oxygen toxicity, and, when this was investigated, garlic did indeed show strong antioxidant and hydroxyl radical-scavenging properties, it is presumed owing to the alliin contained within.
Alliin has been found to affect immune responses in blood.
Alliin was the first natural product found to have both carbon- and sulfur-centered stereochemistry.
The composition and the energy value of garlic is given in Table 7
Table 7 Composition and energy value of 100 g of fresh bulb.
Niacin (vit. B3)
Thiamine (vit. B1)
Riboflavin (vit. B2)
Pantothenic acid (vit. B5)
Pyridoxine (Vit. B6)
Folate (vit. B9)
By analyzing the biomolecular composition of garlic, it has been observed that garlic displays a plethora of biological effects including immunomodulation. Although some immunomodulatory proteins from garlic have been described, their identities are still unknown. The present study was envisaged to isolate immunomodulatory proteins from raw garlic, and examine their effects on certain cells of the immune system (lymphocytes, mast cells, and basophils) in relation to mitogenicity and hypersensitivity. Three protein components of approximately 13 kD (QR-1, QR-2, and QR-3 in the ratio 7:28:1) were separated by Q-Sepharose chromatography of 30 kD ultrafiltrate of raw garlic extract. All the 3 proteins exhibited mitogenic activity towards human peripheral blood lymphocytes, murine splenocytes and thymocytes. The mitogenicity of QR-2 was the highest among the three immunomodulatory proteins. QR-1 and QR-2 displayed hemagglutination and mannose-binding activities; QR-3 showed only mannose-binding activity. Immunoreactivity of rabbit anti-QR-1 and anti-QR-2 polyclonal antisera showed specificity for their respective antigens as well as mutual cross-reactivity; QR-3 was better recognized by anti-QR-2 (82%) than by anti-QR-1 (55%). QR-2 induced a 2-fold higher histamine release in vitro from leukocytes of atopic subjects compared to that of non-atopic subjects. In all functional studies, QR-2 was more potent compared to QR-1. Taken together, all these results indicate that the two major proteins QR-2 and QR-1 present in a ratio of 4:1 in raw garlic contribute to garlic's immunomodulatory activity, and their characteristics are markedly similar to the abundant Allium sativum agglutinins (ASA) I and II, respectively.
It is recently demonstrated that the immunomodulatory proteins present in garlic are identical to the garlic lectins ASA I and ASA II (Clement F, Pramod SN, Venkatesh YP. Int. Immunopharmacol. 2010; 10: 316-324). In this study, the stability of garlic lectins as a function of pH, temperature and denaturants has been examined in relation to biological activity (hemagglutination and phagocytosis). Stability of garlic lectins in simulated gastric fluid (SGF) was assessed by their hemagglutination activity, immunoreactivity, and intactness by SDS-PAGE. Garlic lectins were moderately stable in SGF for up to 30 min; while they retained hemagglutination activities, immunoreactivity with the respective rabbit antiserum decreased immediately (0.5 min) to 10-30%. ASA I retained ~80% hemagglutination activity in the pH range 2-12; however, ASA II retained only 40% in the pH ranges 2-4 and 10-12. Garlic lectins exposed to 60 °C (30 min) and pepsin (1 and 2 min) retained hemagglutination and phagocytic activities. Urea (4M) and Gdn.HCl (2M) did not affect hemagglutination. The immunogenicity of garlic lectins upon oral feeding in BALB/c mice was examined. A lectin-specific serum IgG response was seen in mice comparable to the oral immunogen, phytohemagglutinin. The recovered lectin in feces of mice administered with garlic lectins showed antigenicity identical to that of the administered proteins. The stabilities of the garlic lectins, their ability to withstand the gastrointestinal passage, and their recognition by the immune system upon oral feeding reinforce the reported presence of natural antibodies to garlic proteins in normal human sera.
Further observations on the biomolecular composition of the garlic induces us to consider some studies that demonstrate the possible use of substances constituting the garlic in various fields. In particular, the lectins of the garlic are promising candidate molecules for crop protection against pest insects that have an mug chewer apparatus (Lepidoptera larvae) or an mug apparatus stinging and sucking such as aphid and many other Homoptera.
Molecular mechanism of toxicity and interaction of lectins with midgut receptor proteins has been described in many reports. Lectins show its effect right from sensory receptors of mouth parts by disrupting the membrane integrity and food detection ability. Subsequently, enter into the gut lumen and interact with midgut glycosylated proteins like alkaline phosphatase (ALP), aminopeptidase-N (APN), cadherin-like proteins, polycalins, sucrase, symbionin and others. These proteins play critical role in life cycle of insect directly or indirectly. Lectins interfere with the activity of these proteins and causes physiological disorders leading to the death of insects. Lectins further transported across the insect gut, accumulated in various body parts (like haemolymph and ovary) and interact with intracellular proteins like symbionin and cytochrome p450. Binding with cytochrome p450 (which involve in ecdysone synthesis) might interfere in the development of insects, which results in growth retardation and pre-mature deat
Adversities of the garlic
Diseases of the garlic
Causal agents: Puccinia allii Rudolph, 1829; Puccinia Pers., 1801 spp.
- Taxonomy of Puccinia allii
Nature: Natura, C. Linnaeus, 1758
Physical world: Mundus, Plinius
Natural bodies: Naturalia, Plinius
Natural bodies: Biota
Domain: Eukaryota, Whittaker & Margulis,1978
Kingdom: Fungi, T.L. Jahn & F.F. Jahn, 1949 ex R.T. Moore, 1980 - Fungi
Subkingdom: Dikarya, D.S. Hibbett et al., in D.S. Hibbett et al., 2007
Phylum: Basidiomycota, H.C. Bold, 1957 ex R.T. Moore, 1980 Basidiomycetes
Subphylum: Pucciniomycotina, R. Bauer et al., 2006
Class: Urediniomycetes, R. Bauer et al., 2006
Order: Uredinales, Clem. & Shear, 1931
Genus: Puccinia Pers., 1801
Specific descriptor: allii(DC.) F. Rudolph, 1829
Scientific name: Puccinia allii F. Rudolph, 1829
Puccinia blasdalei Dietel & Holw. 1893; Puccinia mixta Fuckel 1870; Puccinia porri (Sowerby) G. Winter 1882; Uredo ambigua Dc. 1815; Uredo porri Sowerby 1810; Uromyces ambiguus (Dc.) Lév. 1847; Uromyces durus Dietel 1907.
- Symptomatology, identification and control of the disease
In Italy, generally, garlic rust is not considered an economic problem. In some case, in relation to climatic conditions we can observe a severe infection of the disease caused an average 51% reduction in yield throughout the state.
The rust pathogen is comprised of genetically distinct sub-groups which differ in different parts of the world. Most attacks occur from mid-summer until late autumn. The symptoms interest the leaves. Bright orange pustules on both sides of infected leaves. These are initially enclosed by the surface tissues of the leaf, but break open to release dusty, orange, airborne spores
Severe attacks may cause leaves to shrivel prematurely and will reduce vigour.
Infection is worse on nitrogen-rich soils with low potassium, so take care with fertiliser applications. Do not crowd plants, as this raises humidity and increases the likelihood of infection. Dispose of all plant debris at the end of cropping.
Suppliers sometimes claim a degree of resistance for certain varieties, check the latest catalogues for those currently available.
The rust fungi are described as biotrophs; that is, they grow within the living tissues of the plant and extract nutrients from the cells without killing them. However, although they do not kill tissues, heavy attacks by rusts can cause the leaves to shrivel and die prematurely and can depress vigour.
Garlic rust and all the rusts are not able to survive on dead plant material, so must either alternate with a different, perennial host, or produce resting spores to pass the dormant season.
The garlic rust pathogen seems to fulfil its entire life cycle on garlics, without the need for an alternate host. On some other Allium species the fungus begins to produce dark resting spores within the orange pustules as the foliage dies down . These resting spores have been observed occasionally on garlic, but the role that they play in the disease on this crop is currently unknown. It is likely that there are simply sufficient garlic in the ground at all times of the year to ensure continuity of infection, without the need for resting spores.
Puccinia allii has been confirmed as being seed-borne, but this is not currently thought to be of any great significance in the spread of the disease.
It is thought that a number of strains of Puccinia allii exist, varying in their ability to infect different Allium species.
Research carried out demonstrated that the weight of harvested bulbs is 25% to 60% smaller than the average weight in the previous year, and soluble solids were reduced by an average of 15%. Until recently, garlic varieties that are resistant or highly tolerant to rust have not been grown in garlic production fields. Open pollinated progenies derived from 3 Plant Introduction (PI) accessions of the U.S. Dept. of Agriculture-Agricultural Research Service germplasm collection were inoculated with a suspension of urediniospores (1, 2 × 105/mL) isolated from rust infected garlic leaves obtained from production fields. Inoculations were carried out in a replicated experiment in the field under plastic covers, where 12 hours of misting was applied. The disease symptoms were scored on all leaves of the inoculated plants. The size of observed lesions varied from <1 to 280 mm2. Of the 118 plants evaluated, 9.3% had an average leaf area with rust symptoms of less than 1%. The majority of the plants (83.1%) had 1 to 5% of leaf area infected, and over 6% of plants had symptoms on 5 to 25% of their leaf surface. The highest number of plants with a low percent of rust symptoms on leaves was observed on progenies produced from PI 493099. While all maternal plants used to produce the seeds showed rust symptoms, the presence of progenies with ≤0.5% of leaf area infected indicated that a tolerance source to Puccinia allii may exist in the Allium sativum NPGS, germplasm collection.
- Prevention and treatments
- reduction of the nitrogen fertilizations;
- increase of the potassium fertilizations;
- destruction of infected material;
- long rotations;
- 2-3 preventive interventions are carried with copper products or with azoxystrobin, in relation to weather.
Downy Mildew of the garlic:
Causal agent: Peronospora destructor (Berk.) Casp. ex Berk., 1860
- Taxonomy of Peronospora destructor (Berk.) Casp. ex Berk., 1860
Nature: Natura, C. Linnaeus, 1758
Physical world: Mundus, Plinius
Natural bodies: Naturalia, Plinius
Natural bodies: Biota
Domain: Eukaryota, Whittaker & Margulis,1978
Kingdom: Fungi, T.L. Jahn & F.F. Jahn, 1949 ex R.T. Moore, 1980 - Fungi
Subkingdom: Dikarya, D.S. Hibbett et al., in D.S. Hibbett et al., 2007
Phylum: Oomycota, Winter, 1897
Subphylum: Peronosporomycotina, Winter, 1897
Class: Peronosporomycetes, Dick, 2001
Subclass: Peronosporomycetidae, Dick et al., 1984
Order: Peronosporales, Clem. & Shear, 1931
Specific descriptor: destructor (Berk.) Casp. ex Berk.
Scientific name: Peronospora destructor (Berk.) Casp. ex Berk., 1860
Synonyms: Peronospora destructor (Berk.) Casp. ex Berk., Botrytis destructor Berk., 1841, Peronospora schleideni Unger, 1847
- Symptomatology, identification and control of the disease
Downy mildew is a fungal disease affecting garlics and related species, including weedy species. Leaves initially develop pale, elongate patches. The spots may be water-soaked at first, and then later appear somewhat purplish. The spots become covered with a downy, greyish or white fungal growth. Affected leaves often die back. Bulbs of affected plants are smaller than normal and of poor quality. Infected bulbs may become shrivelled and discoloured in storage, or may sprout prematurely. Cool, damp weather favours spread of the disease.
Downy mildew can develop from an initial infection by airborne spores into an epidemic very quickly if humidity and temperature conditions (1.5 to 7 hours of leaf wetness and 6 °C to 27 °C) are favourable. Spores can travel long distances in moist air, but are quickly killed by dry conditions. Initial sources of disease can be infected bulbs, sets, seeds, and plant debris.
The downy mildew pathogen can survive for many years in the soil as oospores. In order to spread and infect plants, they need to have moist conditions. One spore stage of the pathogen is motile (it can swim) so free water is necessary for infection and spread. Additionally, spores may also be spread under windy rainy conditions
Sporangiophores first appeared as outgrowths from stomata on abaxial leaflet surfaces 4-6 h after infected, glass-house-grown plants were exposed to high humidity, at temperature range of 4-25 °C. Sporangiophores continued to develop over the next 6 h, first as simple elongating hyphae, then branching from a single axis (monopodially) to produce multiple, terminal sporangia (that measure 40-72 x 18-29 μm), which developed synchronously and polyblastically on each sporangiophore. Sporangia had smooth surfaces during development, were finely echinulate when mature, and were delimited by septa at the ends of terminal sporangiophore branches. Gametangia (oogonia and antheridia) developed extensively on inner surfaces of field-grown garlic leaves from smooth, bulbous hyphae adhering to the host epidermis. Each oogonium was surrounded by several antheridia. Oospores within leaf tissue of field-grown plants were enclosed by oogonial membranes. Each oospore had a heavily reticulate outer wall enclosing cytoplasm and liquid, possibly lipid. Cryofixation and low temperature scanning electron microscopy have provided new insights into the morphology of reproduction in garlic.
- Prevention and treatments
Agronomic interventions or Cultural Control:
- Avoid overhead watering. Irrigations only when necessary, preferring the morning hours to allow the vegetation to dry;
- Control weeds in and around the garden;
- Plant disease-free materials in well-drained soils;
- Remove and destroy diseased plants and debris;
- Destroy volunteer Allium plants in and around the field and buildings;
- Destroy or discard (do not compost) diseased materials;
- Rotate crops. Do not plant garlics and related crops into the same locations each year;
- Allow at least three years before replanting susceptible crops in a location which was previously diseased;
- Space plantings to provide good air circulation.
spray at the first sign of disease; fungicides may be applied on a 7-day schedule, if necessary. For all fungicides, thorough coverage of foliage is important in the control of downy mildew. Below is a list of fungicides to be administered only in case of absolute necessity.
It must be remembered that the shape and the presence of waxy substances on leaves Liliaceae make difficult the application of fungicides that tend to slip away before having explicate effective action. It is therefore must be careful to the formulation of crop protection and in particular the presence of wetting and other additives. To prevent the emergence of resistance phenomena is also recommended to alternate the active ingredients used.
- Fenamidone: Quinone outside inhibitor. Do not more than one application before alternating with a fungicide that has a different mode of action.
- Mancozeb/Mefenoxam(Ridomil Gold). Dithiocarbamate and Phenylamide. Do not apply to exposed bulb.
- Mefenoxam/Chlorothalonil: (Ridomil Gold/Bravo)
- Chlorothalonil: see label regarding special instructions related to the 12 hour R.E.I.
- Mancozeb (Penncozeb, Dithane): do not apply to exposed bulb.
- Maneb: do not apply to exposed bulb. Not as effective as other materials, but some products are acceptable for use in an organically certified crop.
- Copper: not as effective as other materials, but some products are acceptable for use in an organically certified crop.
The first approach to warning systems consisted of the definition of periods favourable for the disease in Bulgaria (Vitanov, 1971). A similar approach was followed by Palti et al. (1972) who tried to define mildew-free periods analysing 10-year records of weather conditions in relation to the dates of onion mildew outbreak in Israel.
In 1975, a bioclimatological model, based on microclimatic conditions, was developed in the Netherlands to define potential infection dates (Weille, 1975). In the following year, Stenina (1976) tried to forecast the disease in the Krasnodar region (Russia) using weather data.
The first model based on disease cycle was developed by Jesperson and Sutton (1987) in Canada and called DOWNCAST. It defines whether primary infections are, or are not, possible on the basis of the meteorological conditions which are necessary for sporulation, infection and spore survival.
A more detailed approach was followed by Battilani et al. (1996). They applied systems analysis to the onion-downy mildew pathosystem and they obtained ONIMIL, a model able to determine, for each day, the probability of establishing an infection caused by Peronospora destructor and its infection level, compared with the maximum. For practical use, it gives a forecasting of primary infection 7-14 days before its real appearance. Further studies improved the model, pointing out that plants are only sensitive from growth stage F (senescence of the first leaf, appearance of fifth - seventh leaf) (De Visser, 1990). Presence of the inoculum near the field is always necessary for the establishment of infection on seeded onion fields (Battilani et al., 1998).
Causal agent: Fusarium spp. Link, 1809; Helmintosporium spp., Link ex Fries, 1821; Sclerotium cepivorum, Berk (Coley & Smith, 1987); Penicillium spp., Link, 1809.
Basal Rot and White Rot:
- Symptomatology, identification and control of the diseases
The symptoms of basal rot are slow to develop. Often, they are seen as a yellowing and eventual dieback of the leaves. Sometimes one can also see white fungal growth at the bulb base, which will lead to both pre and post-harvest rotting. Postharvest rotting can include single, several or all of the cloves in the garlic bulb.
The symptoms of white rot may look almost identical to basal rot, with the exception that the process of disease initiation to plant death is more rapid. Early symptoms include white, fluffy fungal growth on the stem that extends around the bulb base. Small, dark, over-wintering structures called
sclerotia form in the decayed tissue.
The fungus that causes basal rot prefers high temperatures. It is often considered a weak pathogen, as it will attack plants already damaged by
other diseases or insects. Initial infection often occurs through the basal plate, but not all infected bulbs show disease symptoms. The pathogen is often spread through fields by infected seed or through movement of soil and other debris, transfer from tools or equipment, and in irrigation water.
The fungus that causes white rot prefers temperatures, below 24°C. In northern climates, it attacks plants in the spring. The sclerotia can survive in soil for indefinite periods of time in the absence of garlic or other hosts. Sclerotia are stimulated to germinate in the presence of organic sulphur compounds produced by the plants. Once the plants become infected, disease and rot rapidly ensue, either killing the plant outright or causing rot of bulbs later in storage.
- Prevention and treatments
Agronomic interventions or Cultural Control:
If possible, work in clean fields prior to working in fields where infections or infestations have been found. Clean equipment between fields to avoid moving infested soil from one field to another. Additionally, as with any crop, it is important to plant clean healthy seed. For most of the mentioned diseases (Basal Rot, White Rot, Downy Mildew and Nematode infestation), once the pathogen is
established in a field, rotation away from Allium spp. for several years is an essential management tool. Schematically:
- avoid stagnant water;
- long rotations;
- using healthy propagation material;
- ginning of the bulbs after adequate heating to prevent possible injury;
- hoeing between the rows;
- it has been shown that a hot water treatment of the garlic cloves can reduce infection up to 50%
To realize with the disinfection of cloves, carried out with the following products which are to be used only for this purpose:
There are numerous bacterial diseases reported on the garlic. They are of limited importance, even if sometimes, under certain environmental conditions, can cause serious damages.
The bacteriosis can be classified as follows:
- Taxonomy of the genera of bacteria causal agents of the mentioned garlic diseases
- Bacterial flower stalk and leaf necrosis
- Pantoea agglomerans (Ewing and Fife 1972) Gavini, Mergaert, Beji, Mielcarek, Izard, Kersters and De Ley 1989: the disease is distributed in Peru, Poland, South Africa and USA (Colorado, Georgia, Michigan and New York). The symptoms first appear as whitish to tan lesions with water-soaked margins, often on interior leaves. Foliar lesions can rapidly coalesce, progressing to wilt and dieback of affected leaves. The pathogen moves from the leaves into the neck and bulb causing yellowish to light-brown discoloration. With severe infections, all leaves can be affected giving a bleached appearance to plants. Secondary bacterial infections rot interior bulb tissue and produce a foul odour. Under conditions favourable to the disease, yield losses may approach 100%. The pathogen is seed-borne and can survive on a few reported alternate hosts (corn, cotton, melon, pineapple, rice and sugar cane). They may also survive epiphytically on weeds and crop debris. Spread can occur by wind, splashing water and thrips. Infection is favored by moderate to warm temperatures and rainfall during bulb initiation.
Control: Seed produced in high risk areas should be tested for Pantoea ananatis and Pantoea agglomerans before sowing. Some garlic and onion varieties are known to be more susceptible to this disease than others. Avoid planting these varieties where disease pressure is high. Control weeds, volunteer garlics, onions and thrips. Consider drip rather than sprinkler irrigation if possible, and avoid working in fields when foliage is wet. Avoid excessive nitrogen fertilization. If applied preventively, copper-based bactericides may provide control under low to moderate disease pressure. Initiate sprays two weeksbefore bulbing and continue every 5-7 days thereafter. Deep cultivate after harvest to promote decomposition of crop debris. Where this disease occurs, a minimum three-year rotation to non-hosts is recommended.
- Erwinia herbicola (Loehnis 1911) Dye 1964: garlic plants in an experimental field at Beit Dagan (Israele) developed a whitish leaf tip dieback in late November 1993. Infected plants were smaller and produced smaller bulbs than healthy plants. Yields were reduced by 35% compared with similar plots which were not disease affected was identified as the causal organism. The very warm winter and the overhead sprinkler system used in the field are thought to have caused the outbreak. Similar but milder symptoms were observed in the 1994-95 and 1995-96 crops, in which only leaf tips were affected and no major yield losses occurred. Erwinia herbicola was isolated from lesions on infected plants in both years [M. F. Koch, Z. Taanami, E. Levy, 1996. Damage to garlic crops caused by Erwinia herbicola. Phytoparasitica 24(2), 125-126]. Bacterial soft rot is mainly a problem on mature bulbs. Affected scales first appear water-soaked and pale yellow to light brown when infected by Dickeya chrysanthemi or bleached gray to white when infected with Pectobacterium carotovorum subsp. carotovorum. As the soft rot progresses, invaded fleshy scales become soft and sticky with the interior of the bulb breaking-down. A watery, foul-smelling thick liquid can be squeezed from the neck of diseased bulbs.
- Pseudomonas marginalis pv. marginalis (Brown) Stevens 1925: economic losses arise from reduced marketability of the crop, the presence of diseased stored product, and yield reduction. There are no data available on the economic importance of rots in the field and in storage caused by fluorescent pseudomonads, including Pseudomonas marginalis pv. marginalis in the European area. In many cases they only appear to be opportunistic pathogens.
- Bacterial Blight
- Pseudomonas syringae van Hall 1902 pv. porri Samson, Poutier & Rat 1981: the disease first appears as dark-green, longitudinal, water-soaked lesions that form at leaf tips and edges. As they elongate, lesions turn orange to brown with surrounding chlorosis and may extend as a narrow strip from leaf tip to the sheath. When a lesion extends into the sheath, the affected leaf turns light-green, curls, splits and eventually wilts and dies. Severely affected plants are misshapen, undersized and cannot be harvested. Infested seed and infected garlic debris from a previous crop are both sources of primary inoculum. The bacterium may infect but remain latent in the plant until environmental conditions favour development of disease. Generally, warm temperatures and high humidity encourage symptom expression and disease spread. The disease was observed during 1996 and 1997, such as a new and damaging disease of leek, on greenhouse-produced transplants and field-grown plants in California. Pathogenicity tests established that representative strains of this P. syringae induced disease symptoms in leek that were similar to those observed on leek plants in the greenhouse and field, and that this bacterium caused similar symptoms in onion, chives, and garlic plants. Representative strains were further characterized by fatty acid analysis, repetitive bacterial sequence-polymerase chain reaction (rep-PCR), and rDNA sequencing. Fatty acid analysis confirmed that these isolates were P. syringae, but did not provide a clear pathovar designation. Rep-PCR analysis revealed that all the California leek P. syringae strains had identical DNA fingerprints and that these strains were indistinguishable from those of known strains of P. syringae pv. porri. In addition, the rDNA sequence of the spacer region between 16S and 23S rDNA genes was identical among the California leek P. syringae strains and P. syringae pv. porri. Together, these results established that the new leek disease in California is caused by P. syringae pv. porri. P. syringae pv. porri was recovered from a commercial leek seed lot imported into California, which suggests that the pathogen was introduced in association with seed. Commercial leek production in California is favourable for development of this disease because transplants are produced in greenhouses with high plant densities, overhead irrigation, and mowing of plants.
Control: sow only clean seed. During the growing season, limit overhead irrigation and avoid mowing the crop when plants are wet with dew or rain. Removing infected plants and plant debris throughout the season and rotating to a non-host help mitigate the risk of disease. Apply soil amendments as needed to increase soil pH to at least 5.5 to reduce the chance of infection.
- Bacterial internal brown rot of bulbs
- Pseudomonas aeruginosa (Shroeter 1872) Migula 1900.
- Bacterial leaf spot and flower stalk necrosis
- Pseudomonas fluorescens (Flügge) Migula 1895: it cause garlic leaf rot and was reported for the first time in Italy (Calzolari and Bazzi, 1985). This bacteriosis is already known in France as "cafe au lait" disease, due to the colour of the infected tissues. Although it causes pseudostem rot, disease progression does not hinder bulb formation, but makes the external tunics torn and dark brown. On the basis of the characteristics studied during identification, the pathogenic strains of the bacterium could be allocated to biovar I (Palleroni,1984). The role of nematodes and insects in favouring the penetration of germs through wounds caused by them is also considered.
- Bacterial leaf streak and bulb rot
- Pseudomonas viridiflava (Burkholder 1930) Dowson 1939: it is the causal agent of necrotic spots on onion and garlic leaves in Uruguay. The first symptoms observed are oval, water-soaked leaf lesions, tip-burn and leaf streaking of varying lengths. Initially, leaf streaks are green but eventually darken to black. As infections become more severe and spread down the leaf, entire leaves collapse and dry. Leaf distortion and twisting may also occur. Bulb infection is characterized by dark spots on outer scales and reddish brown discoloration of inner scales. Symptoms often develop in a ring-like pattern due to restriction of the rot by the scales. This disease occurs particularly in winter and spring when temperatures are cool. Epidemics are associated with prolonged periods of rain, which favour progression of the disease. Excess fertilizer stimulates disease development. It is thought that frost damage may predispose onion plants to infection.
Control: Applications of fixed copper compounds or streptomycin inhibit spread of this disease although bacterial strains resistant to copper may occur. Excessive fertilizer applications may increase foliar symptoms and should be avoided. Reduce postharvest rot by harvesting onions at the proper maturity stage, by reducing wounding and bruising during harvest and by proper curing of bulbs with forced hot air.
- Bacterial soft rot
- Dickeya chrysanthemi Samson et al., 1953 = Erwinia chrysanthemi Burkholder et al. 1953: distributed in Mexico and USA, the bacterial soft rot is mainly a problem on mature bulbs. Affected scales first appear water-soaked and pale yellow to light brown when infected by Dickeya chrysanthemi or bleached gray to white when infected with Pectobacterium carotovorum subsp. carotovorum. As the soft rot progresses, invaded fleshy scales become soft and sticky with the interior of the bulb breaking-down. A watery, foul-smelling thick liquid can be squeezed from the neck of diseased bulbs. Bacterial soft rot is most common in storage crops or transit; however, this disease can develop on onions and garlic in the field before harvest, after heavy rains and when leaves are drying. The main sources of inoculum are contaminated soil and crop residues. The bacteria is spread by splashing rain, irrigation water and insects. Entry into bulbs is only through wounds such as those caused by transplanting, mechanical injuries or sunscald. Also, garlic can carry soft rot bacteria and introduce them while feeding. This disease is favoured by warm, humid conditions with an optimum temperature range of 20-30°C. However, during storage or transit soft rot can develop when temperatures are above 3°C.
Control: avoid overhead irrigation where possible, and control insect pests such as the onion maggot. Disease spread and infection may be reduced by copper-based bactericides. Allow garlic tops to mature before harvesting and avoid damaging bulbs during harvest. Store onion bulbs only after they have been properly dried, and provide the appropriate temperature and humidity with good ventilation to prevent moisture condensation from forming on the bulbs.
- Pectobacterium carotovorum subsp. carotovorum (Jones 1901) Waldee 1945 emend. Hauben et al. 1999 = Erwinia carotovora subsp. carotovora (Jones 1901) Bergey et al. 1923: the pathogen is the co-causal agent of bacterial soft rot.
- Erwinia rhapontici (Millard 1924) Burkholder 1948: the bacteria invaded fleshy scales become soft and sticky with the interior of the bulb breaking-down.
- Pseudomonas marginalis pv. marginalis (Brown 1918) Stevens 1925.
- Center rot
- Pantoea ananatis (Serrano 1928) Mergaert et al. 1993 = Erwinia ananatis Serrano 1928: The disease is distributed in Peru, Poland, South Africa and USA (Colorado, Georgia, Michigan and New York). Symptoms first appear as whitish to tan lesions with water-soaked margins, often on interior leaves. Foliar lesions can rapidly coalesce, progressing to wilt and dieback of affected leaves. The pathogen moves from the leaves into the neck and bulb causing yellowish to light-brown discouloration. With severe infections, all leaves can be affected giving a bleached appearance to plants. Secondary bacterial infections rot interior bulb tissue and produce a foul odor. Under conditions favorable to the disease, yield losses may approach 100 percent.Both pathogens are seedborne and can survive on a few reported alternate hosts (corn, cotton, melon, pineapple, rice and sugar cane). They may also survive epiphytically on weeds and crop debris. Spread can occur by wind, splashing water and thrips. Infection is favored by moderate to warm temperatures and rainfall during bulb initiation.
Control: seed produced in high risk areas should be tested for Pantoea ananatis and Pantoea agglomerans before sowing. Some onion varieties are known to be more susceptible to this disease than others. Avoid planting these varieties where disease pressure is high. Control weeds, volunteer garlics, onions and thrips. Consider drip rather than sprinkler irrigation if possible, and avoid working in fields when foliage is wet. Avoid excessive nitrogen fertilization. If applied preventively, copper-based bactericides may provide control under low to moderate disease pressure. Initiate sprays two weeks before bulbing and continue every 5-7 days thereafter. Deep cultivate after harvest to promote decomposition of crop debris. Where this disease occurs, a minimum three-year rotation to non-hosts is recommended.
- Enterobacter bulb decay
- Enterobacter cloacae (Jordan 1980) Hormaeche & Edwards 1960: the disease is distributed in Poland and USA (California, Colorado, New York, Utah and Washington). The exterior of the bulb remains asymptomatic while the inner scales show a brown to black discoloration and decay. This disease was observed in mature bulbs in the field after a period where air temperatures had reached 40-45°C. The bacterium is common in many environments and is considered to be an opportunistic pathogen on garlics. No control measures have been reported.
- Slippery skin
- Burkholderia gladioli pv. alliicola (Burkholder 1942) Young et al. 1996 = Pseudomonas gladioli pv. alliicola (Burkholder 1942) Young, Dye & Wilkie 1978: worldwide distributed, the field symptoms often appear as one or two wilted leaves in the centre of the leaf cluster. These leaves eventually turn pale yellow and dieback from the tip while older and younger leaves maintain a healthy green appearance. During the early stages of this disease, the bulbs may appear healthy except for a softening of the neck tissue. In a longitudinal section, one or more inner scales will look watery or cooked. The disease progresses from the top of the infected scale to the base where it can then spread to other scales, rather than by spreading crosswise from scale to scale. Eventually, all the internal tissue will rot. Finally, the internal scales dry and the bulb shrivels. Squeezing the base of infected plants causes the rotted inner portion of the bulbs to slide out through the neck, hence the name slippery skin.
Control: harvest garlics when bulbs have reached full maturity. Do not store bulbs until they have been properly dried. Minimizing stem and bulb injury and avoiding overhead irrigation when the crop is approaching maturity can reduce losses from this disease. Bulbs should be stored at 0-2°C with adequate ventilation to prevent condensation from forming on the bulbs.
- Sour skin
- Burkholderia cepacia (Palleroni & Holmes 1981) Yabuuchi et al. 1993 = Pseudomonas cepacia (ex Burkholder 1950) Palleroni & Holmes 1981: worldwide distributed, the field symptoms often appear as one or two leaves that have turned a light brown colour. A watery rot develops at the base of the leaves and proceeds into the neck, allowing the leaves to be easily pulled from the bulb. As the disease progresses the outer bulb scales are infected. However, the outer most bulb scales and inner bulb scales may not become infected, which distinguishes sour skin from slippery skin where inner bulb scales are infected first. Infected scales develop a slimy pale yellow to light brown decay and may separate from adjacent scales allowing the firm centre scales to slide out when the bulb is squeezed. Infected bulbs often have an acrid, vinegar-like odour due to secondary invaders, especially yeasts, colonizing decaying bulbs. Bacterium is commonly spread by heavy rains, overhead irrigation and flooding which splash the bacteria onto young or wounded foliage. Infection typically occurs through wounds including those made when garlics are cut at harvest. Infection can also occur when water lands on upright leaves and flows into leaf blade axils carrying the bacterium with it. Sour skin is favoured by rainstorms and warm weather, and develops rapidly at temperatures above 30°C. This bacterium requires moisture for infection and grows in the temperature range of 5-41°C . Severe disease can occur during periods of high rainfall combined with strong winds or hail. Heavy irrigation and persistent dews are also conducive to this disease. This bacterium is soil-borne and can be readily water-splashed to the foliage and necks where it can enter through wounds. As the plant matures it increases in susceptibility with the mature plant being highly susceptible. In warm weather, approximately 30°C, infected bulbs can decay within 10 days. However, in storage decay moves slowly, often requiring 1-3 months for a bulb to decay completely.
Control: the use of furrow irrigation, instead of overhead and recycled irrigation water, will reduce losses from this disease. Do not damage foliage prior to harvest or bulbs during harvest since B. cepacia enters the plant primarily through wounds. Onion and garlic crops should be harvested at maturity and the bulbs dried quickly. Storing onions at cool temperatures 0°C with adequate ventilation to prevent condensation on the bulbs will reduce storage losses resulting from this disease.
- Xanthomonas axonopodis pv. allii (Dowson 1939) Roumagnac et al. 2004: leaf blight: symptoms first appear as white to tan flecks, light-coloured spots and/or lenticular lesions surrounded by water-soaking. Lesions rapidly enlarge, turning tan to brown with extensive water-soaking. As the disease progresses, lesions coalesce into dry necrotic areas of tip dieback. Typically, blighting of outer, older leaves leads to plant stunting and undersized bulbs. When conditions are favourable for disease, all leaves may become completely blighted and plant death may follow. Symptoms in leek, shallot, chives, and garlic are similar to those in onion but are less severe. Short-day onion varieties may develop symptoms at any stage of crop development, and long-day onion varieties usually develop symptoms during or after bulb-initiation. Disease is favoured by temperatures above 26 °C. Frequent rains and high humidity promote disease development. Severe outbreaks are often associated with heavy rain, hail and wind-blown sand that damages foliage. Symptoms usually appear 7-10 days later. Spread of the pathogen within and between fields occurs with both overhead and furrow irrigation and movement of residual garlic debris by field equipment. The pathogen is also seed-transmitted. Frequent rains and overhead irrigation can initiate an epidemic from contaminated seed in semi-arid environments. The bacterium survives on contaminated seed, in infested crop debris and as an epiphyte or pathogen on volunteer garlics, onions, legumes and weeds. The geographic distribution is Brazil, the Caribbean, Japan, Reunion Island (France), South Africa, USA and Venezuel.
Control: Use only clean seed or transplants. Rotate to non-hosts for at least two years. Do not plant onion or garlic after dry beans, soybeans or alfalfa which may harbor this pathogen. Control volunteer onions and weeds in and around fields. During the growing season avoid overhead irrigation and excessive nitrogen fertilization. Copper bactericides alone or in combination with recommended fungicides can be effective in semi-arid regions when applied prior to the onset of symptoms. Incorporate crop debris into soil promptly after harvest.
Nature: Natura, C. Linnaeus, 1758
Physical world: Mundus, Plinius
Natural bodies: Naturalia, Plinius
Class: Gamma Proteobacteria
Genus: Pantoea Gavini et al. 1989
Genus: Erwinia Winslow et al. 1920
Genus: Dickeya Samson et al. 2005
Genus: Enterobacter Hormaeche & Edwards 1960
Nature: Natura, C. Linnaeus, 1758
Physical world: Mundus, Plinius
Natural bodies: Naturalia, Plinius
Class: Gamma Proteobacteria
Genus: Pseudomonas Migula 1894
Nature: Natura, C. Linnaeus, 1758
Physical world: Mundus, Plinius
Natural bodies: Naturalia, Plinius
Class: Gamma Proteobacteria
Genus: Xanthomonas Dowson 1939
Nature: Natura, C. Linnaeus, 1758
Physical world: Mundus, Plinius
Natural bodies: Naturalia, Plinius
Class: Beta Proteobacteria
Genus: Burkholderia Yabuuchi et al. 1993 emend. Gillis et al. 1995
Iris yellow spot tospovirus (IYSV):
- History of Iris yellow spot tospovirus in the World
A pathogen, described as Tomato spotted wilt virus (TSWV), was reported affecting onion inflorescence stalks (scapes) in southern Brazil in 1981. The disease was characterized by symptoms of chlorotic and necrotic eye-like or diamond shaped lesions on scapes, and later was referred to as sapeca. Similar symptoms were observed in the United States in summer of 1989 in onion seed crops in the Treasure Valley of south-western Idaho and eastern Oregon (USA). Symptoms appeared as chlorotic or necrotic, straw-colored to white, dry, elongate or spindle-shaped lesions along the scape, with lesions frequently more numerous at mid- to lower portions of the scape. In some lesions, an island of green tissue developed in the center of the necrotic area. When lesions became large and numerous, they coalesced, often completely girdling the scape. This weakened the scape, causing the seed head to collapse and topple over. Patterns of disease incidence in fields or locations were not apparent, nor was there any association with host genotype or cultural practices. Estimated yield losses in individual fields ranged from insignificant to nearly 60%.
Transmission electron microscopy of extracts and thin sections of symptomatic scape tissue revealed the presence of virus particles morphologically similar to TSWV. Inoculation of Gomphrena globosa with sap prepared from symptomatic tissues resulted in development of necrotic lesions; however, serological tests for TSWV and Impatiens necrotic spot virus (INSV) were negative. Together, these results indicated the possible involvement of a new tospovirus, although tospoviruses infecting onion had
been reported previously. Subsequently, Moyer and Mohan and Hall et al. reported the transmission of two tospovirus-like viruses from symptomatic scapes to Nicotiana benthamiana. One group of isolates reacted strongly with polyclonal and monoclonal antisera to INSV, whereas the second group of isolates did not react with INSV or TSWV antisera. In 199293, this new onion infecting tospovirus was detected in vegetative tissues of onion seed crops from Idaho, Oregon, Arizona, and California (USA) by inoculation of N. benthamian a followed by Western blot analysis. The virus was also detected in leek and chive seed crops in Idaho. The disease in Brazil was not reported from that country again until 1994, when it was detected in north-eastern
Brazil; the authors of the report described the causal agent of sapeca in onion as a tospovirus with a serologically distinct nucleocapsid protein. In 1998, Cortes et al. described Iris yellow spot virus (IYSV) in the Netherlands as a new tospovirus naturally infecting iris (Iris hollandica) in the field and leek in the greenhouse. Near the same time, Gera et al. reported that IYSV caused a disease referred to as straw bleaching on onion in Israel, which was characterized by straw-coloured ring spots on leaves and flower stalks that sometimes coalesced and caused premature plant death. The following year, an isolate of the tospovirus causing sapeca was identified as IYSV based on biological, serological, and molecular data. Kritzman et al. reported natural IYSV infection of lisianthus (Eustoma russellianum) grown in the field in Israel. The onion isolate of the tospovirus identified in the United States from 1989 also proved to be IYSV based on molecular and serological data.
Based on recent accounts, IYSV is now known to occur on onion in the following locations: India, 1999, Slovenia, 2000, Colorado (USA), 2002, Australia, 2003, (21,55), Italy, 2004, Japan, Georgia (USA), New Mexico (USA), Washington (USA), Chile, Peru, Spain, Tunisia, central Oregon (USA), 2005 and Reunion Island, Guatemala, Texas (USA), and New York (USA), 2006. To our knowledge, the pathogen has not yet been introduced into other onion-producing regions of the mid-western United States (i.e., Michigan, North Dakota) and Ontario, Canada. With increased awareness of the characteristic symptoms of iris yellow spot, together
with the availability of rapid diagnostic protocols, it is likely that IYSV will be found in onion crops in many other parts of the world. Some evidence suggests iris yellow spot, or a disease with similar symptoms, may also be caused by TSWV or co-infection of TSWV and IYSV. Mullis et al. found that nearly 7% of the onion plants with iris yellow spotlike symptoms in Georgia (USA) were infected with TSWV and IYSV. TSWV has not been reported on onion outside of Georgia (USA), and the significance of TSWV infection or co-infection with IYSV on onion remains speculative. To date, at least 47 plant species have been reported to be infected naturally by IYSV under field conditions. Reported natural hosts of IYSV or its variants include iris, onion, leek, chive, shallot (A. cepa var. ascalonicum), garlic, certain wild Allium species, prairie gentian/lisianthus (Eustoma russellianum, E. grandiflorum), Alstroemeria sp., amaryllis (Hippeastrum hybridum), Amaranthus retroflexus, and Portulaca oleracea. Ghotbi et al. reported IYSV from Cycas sp., Pelargonium hortorum, Rosa sp., and Scindapsus sp. in Iran. In Georgia (USA), found 20 weed species that tested positive serologically for IYSV; the most commonly infected weeds were Vicia sativa, Geranium carolinianum, and Linaria canadensis. Ben Moussa et al. reported detecting IYSV in pepper (Capsicum annuum), potato (Solanum tuberosum), and tomato (Lycopersicon esculentum) in Tunisia. It is unclear if these hosts were infected naturally or by artificial inoculation, and what, if any, disease symptoms were produced on these hosts. To our knowledge, this is the only report of IYSV infection of solanaceous hosts, other than Nicotiana benthamian a and N. rustica indicator plants. Gent et al. reported the rapid expansion of iris yellow spot in onion production regions of Colorado (USA). In two years, iris yellow spot went from being detected in 6 to 73% of the fields surveyed in the eastern and western production areas, but it was not detected in onion fields in north-eastern and southern Colorado (USA) until 2004 and 2006, respectively. The epidemic of iris yellow spot in Colorado (USA) in 2003 was estimated to have cost growers $2.5 to $5.0 million in farm receipts alone, based on a conservative 5 to 10% loss of a $50 million annual revenue. If this rate of spread and damage were to continue, projected economic impact in the western United States could reach $ 60 million (10% loss) to $ 90 million (15%), in addition to environmental and economic costs due to additional pesticide sprays for thrips control ($ 7.5 to $ 12.5 million dollars for three to five additional sprays on 48,500 hectares per year). Iris yellow spot represents an immediate and serious threat to sustainable and productive onion cropping systems in the United States, and the recent detection of this disease in numerous onion-producing countries underscores the need to develop economically sound and effective IPM strategies.
- Epidemiology of Iris Yellow Spot and the Onion Thrips Vector
- Onion thrips as a vector of IYSV. IYSV is transmitted by the onion thrips, Thrips tabaci. Transmission of IYSV has not been reported with populations of Frankliniella occidentalis or F. schultzei, although these thrips species have a broad host range and are efficient vectors of other tospoviruses on numerous plants. Studies in Israel demonstrated a positive relationship between the incidence of T. tabaci in onion crops and the incidence of plants infected with IYSV. Similar to other tospoviruses, IYSV is thought to be acquired by larvae of T. tabaci, with transmission occurring by second larval
instars and adults only after circulation and replication in the vector.
- Spatial and temporal patterns of iris yellow spot epidemics. The spatial and temporal patterns of spread of iris yellow spot in onion crops are largely unknown. Disease incidence varies within and among onion fields and depends on cultivar, plant population, and location in the field. Distinct directional disease gradients commonly are observed in fields during epidemics, but the significance and basis of these disease gradients remain unclear. In Colorado (USA), disease gradients were not consistently related to prevailing wind direction or the bordering crop, but more likely reflected a complex interaction of host susceptibility related to plant stress, proximity to an inoculum source, and vector dispersal and abundance over time. A low but significant degree of spatial autocorrelation in disease incidence has been documented in onion bulb crops, indicating aggregation of diseased plants and possibly secondary spread of the virus within fields. The severity of epidemics of iris yellow spot varies from year to year, although the
incidence of symptomatic plants generally increases markedly after bulb initiation. In preliminary studies, Fichtner et al. and Hammon found only trace levels (< 3% incidence) of symptoms were apparent in onion fields before bulb initiation, with the incidence of disease increasing to 40% or greater as plants approached maturity. The timing of plant infection by IYSV remains uncertain. Surveys of summer bulb crops in eastern Colorado (USA) found a low incidence (< 2%) of infected plants soon after emergence. However, the timing of infections varies among onion bulb and seed crops. Although severe seedling infection was documented in one fall direct-seeded onion seed crop in Washington, symptoms typically develop most rapidly in onion seed crops after emergence of the scapes in late spring in this region. In Georgia (USA), infections appear to occur in the fall soon after planting, which can cause stand establishment problems; whereas severe epidemics of the disease have not been reported closer to harvest. The association in space and time of populations of T. tabaci with outbreaks of iris yellow spot has been suggested in several studies, although quantitative evaluations of the relationships of vector populations with iris yellow spot epidemics have not been reported. Kritzman et al. suggested a relationship between populations of T. tabaci and the incidence of IYSV infection on onion crops in Israel, although the association of disease with population density of the vector was not quantified.
- Detection of IYSV in onion plants. IYSV is distributed unevenly within onion plants. The highest titers of the virus are usually detected in the inner (younger) onion leaves at the center of the whorl or neck, the site where thrips preferentially reside and feed. Unlike TSWV, IYSV infections do not appear to become systemic in onion or other host species, and reliable detection of IYSV using enzymelinked immunosorbent assay (ELISA) can be problematic. The virus typically is not present in all leaves, and generally only is detected by ELISA in tissue sampled within 30 to 50 mm of visible lesions. Although ELISA has been used extensively for detection of IYSV, detection sensitivity is relatively low, and false negative results, even from symptomatic tissues, have been
reported. Problems with false negatives can be reduced by macerating tissues in liquid nitrogen prior to the addition of extraction buffer in ELISA, or by using reverse-transcription polymerase chain reaction (RT-PCR) assays to detect IYSV. Smith et al. reported false positive results with ELISA, and they developed a modified procedure and sampling protocol to minimize
false positives and improve the reliability of IYSV detection from leek. IYSV does not appear to be seed-borne or seed-transmitted in onion. Kritzman et al. did not detect IYSV in the bulbs or roots of infected onion or Hippeastrum plants in Israel. Roubene-Soustrade et al. surveyed onion production fields in Reunion Island, France, and found that 75% of symptomatic leaves and 27% of bulbs tested positive for IYSV using ELISA. This is the only report of bulb infection by IYSV, but it suggests there is a potential for spread of IYSV by distribution of infected bulbs or culled bulbs, as documented for TSWV in the bulbs of Dahlia sp.
- Population structure and sequence characteristics of IYSV isolates. IYSV belongs to the genus Tospovirus and consists of a segmented genome with three genomic RNAs: large (L), medium (M), and small (S). Considerable serological divergence exists among tospoviruses, as indicated by a lack of cross reaction among antisera to some of the distinct virus species within the genus. The nucleotide sequences of the M and S RNAs of IYSV are available, making PCR-based detection of the virus now possible. Molecular studies of IYSV and the sequence diversity among isolates collected from several countries and the western United States
have been reported. Isolates of IYSV obtained from onion and Hippeastrum were identical serologically, and that a 32.5 kDa Mr observed by polyacrylamide gel electrophoresis for the nucleocapsid protein of these isolates was consistent with those published for a Dutch isolate of IYSV. The amino acid sequence of
the nucleocapsid protein of an onion isolate of IYSV showed 99% identity with a lisianthus isolate, and the two isolates showed 96 and 91% identity with a Dutch and a Brazilian isolate of IYSV, respectively. Phylogenetic analysis of the nucleoprotein sequence of IYSV isolates from the western United States revealed three distinct populations. One clade consisted largely of U.S. isolates (California, Colorado, Idaho, Oregon, Texas, Utah, and Washington). Within this clade, there is two subclade: the first had two isolates from Japan, while the second subclade consisted of isolates from the western United States. A second clade largely consisted of isolates from other countries with the exception of isolates from California and Oregon. The clustering of isolates from California in the first clade and in second clade was reported recently, and may suggest multiple introductions of IYSV at different times. IYSV isolates from Brazil and Slovenia showed significant divergence from those in the second clade. Isolates from Chile formed a third clade which was reported to contain isolates from Georgia (USA), Peru, and Guatemala. The clustering of Georgia isolates with those
from Peru suggests possible introduction of IYSV from Peru. Overall, Phylogenetic analysis based on the N protein sequences indicates clustering of isolates based on geographic origin to some extent. Such divergence based on geographic origin was also noted for TSWV, and it is consistent with earlier reports for IYSV. A subgroup of isolates was detected from infected chive, and suggested that this group may constitute a tospovirus that is distinct from IYSV. The implications of the genetic diversity among isolates of IYSV remain speculative, although molecular studies point to multiple introductions of IYSV into the western United States. Genetic diversity among isolates of IYSV may indicate ecological or host specialization. Pozzer et al. detected 9.5% divergence in the amino acid sequence of the nucleocapsid protein of an isolate of IYSV from onion in Brazil (designated IYSVBR) compared with an isolate from iris in the Netherlands. They suggested this divergence reflected an adaptation of the two isolates to different environmental conditions, as supported by differences in host range and host response. Unlike TSWV, genetic diversity among isolates of IYSV has not been associated with differences in vector specificity.
- Overwintering and alternate hosts. Numerous annual and perennial weeds serve as sources of TSWV and its thrips vectors, especially in the south-eastern United States. Similarly, T. tabaci has an extremely broad host range, including weed hosts, especially common winter annuals such as mustard species. These weed hosts may serve as overwintering hosts for IYSV and the onion thrips vector in some onion-producing regions. Preliminary surveys of common weed species in and around onion fields with a history of iris yellow spot in Colorado (USA) in 2004 and 2005 revealed a low incidence of the virus in asymptomatic plants of redroot pigweed (Amaranthus retroflexus) and common purslane (Portulaca oleracea) as determined by ELISA.
It is reported detection of IYSV in 20 potential weed hosts in Georgia (USA) by ELISA. To our knowledge, however, no studies have documented thrips transmission of IYSV from a weed host to onion. In addition to weed hosts, IYSV also may survive on alternate crop hosts grown in the same region as onion. In the Bet-Shean Valley of Israel, the overlapping growing seasons of onion and Hippeastrum are thought to contribute inoculum for successive crops. The association of IYSV with volunteer onion plants has been well established. In Colorado (USA), IYSV has been detected in volunteer onion plants, originating from bulbs left in the field at harvest, growing in ensuing crops of dry bean, alfalfa, field corn, and carrot. Symptomatic volunteer onion plants were detected as early as 1 March, nearly 4 weeks before the summer onion crop was planted, suggesting infected volunteers may provide a biological bridge between onion crops. IYSV typically is not present or detectable in onion bulbs or roots, so the means by which volunteers become infected is uncertain. Volunteer onions may become infected soon after emergence early in the spring as a result of feeding by overwintering viruliferous thrips associated with the bulbs or with nearby plant debris. Alternatively, volunteers may initially be free of IYSV, and become infected by viruliferous thrips migrating from infected, and so far unidentified, overwintering weed host(s). During 2004 and 2005, onion transplant seedlings removed directly from crates after transport from south-western states where they were grown (i.e., Arizona and California, USA) were assayed for IYSV by ELISA. More than 50% of lots of onion
transplants sampled from commercial shipments into Colorado (USA) during 2004 and 2005 exhibited symptoms of iris yellow spot, and the presence of the virus was confirmed by ELISA. The incidence of iris yellow spot symptoms among transplant seedlings within a lot ranged from 0.4 to 5.0%. Additionally, T. tabaci and Frankliniella spp. were recovered from 18 and 91% of the lots sampled in 2004 and 2005, respectively (3 to 275 larvae and/or adults per 200 plants). These and other surveys strongly suggest transplants are a potential source of the virus and vector that may need to be addressed in the production of onion bulb and seed crops. The importance of overwintering of IYSV in diapausing or quiescent thrips in the soil, or associated with plant debris,
has not been investigated, but overwintering of viruliferous thrips in soil potentially could be a source of inoculum. However, overwintering of TSWV in F. fusca and other thrips vectors in the soil general is minimal, and largely has been discounted
as a primary means of survival of this virus.
- Epidemiological aspects of IYSV that differ from other tospoviruses. Although many epidemiological characteristics of iris yellow spot are similar to diseases caused by other tospoviruses, certain epidemiological and biological characteristics of IYSV appear distinct. Vector and host specificity appear to be narrower for isolates of IYSV compared with other tospoviruses. At least nine species of thrips are known to vector strains of TSWV, but T. tabaci is the only known vector of IYSV. More than 650 species of plants from over 50 families have been reported as hosts of TSWV, but the host range of IYSV appears more limited, with most natural hosts in the Liliaceae. As stated above, at least 47 plant species have been demonstrated to be infected naturally by IYSV in the field. Although the host range of T. tabaci is very broad, the host range of IYSV is relatively limited and few of the known hosts are present at a time that would enable overwintering of the pathogen. The propensity of thrips to develop very large populations on onion in short periods of time may strongly influence epidemics of iris yellow spot. Onion is a preferred host for T. tabaci, and this vector is a major pest of onion wherever it is grown. In contrast, tomato is a poor reproductive host of F. occidentalis, which is one of the primary vectors of TSWV on this crop (100). Lewis estimated that 1 hectare of onion may contain 1.6 billion thrips larvae, a tremendous population size given the small stature of onion plants. If left untreated, thrips populations commonly approach 13 to 25 per leaf, although populations as low as 1 to 3 thrips per leaf are capable of causing economic injury in the absence of iris yellow spot. The potential for large outbreaks of thrips, particularly in the warm and dry growing conditions found in much of the western United States, and the potential for thrips to predispose plants to disease may be
central to the epidemiology of iris yellow spot. Secondary spread of IYSV may be significant in disease epidemiology, although
secondary spread of other tospoviruses generally has been regarded as of little consequence to epidemic development. Several studies
have suggested that secondary spread of tomato spotted wilt within fields is limited, and the general failure of insecticides to provide disease suppression is often ascribed to the lack of secondary spread of thrips within fields and the near continuous immigration of viruliferous thrips into fields from weeds and/or other crops. This is reasonable given that TSWV has a broad host range and commonly is found in weed populations. Most studies of the spatio-temporal aspects of diseases caused by tospoviruses have been conducted with TSWV and crops of relatively large stature, such as tobacco and tomato. In contrast, the small stature of onion plants allows for dense plantings, compared with tobacco or tomato, and thrips may readily move between adjacent onion plants. Fichtner et al. and Gent et al. reported a small but significant degree of spatial autocorrelation in the incidence of iris yellow spot within onion fields in Colorado (USA). Here, iris yellow spot was first observed on the borders of the fields, but disease gradients later developed and extended into the fields. Disease gradients extended farther into the field and flattened with time, consistent with secondary spread of the disease from initial infection sites. Correspondingly, Hammon observed a negative correlation between thrips control with insecticides and subsequent development of iris yellow spot. This suggests that secondary
spread of viruliferous thrips may play a role in disease development. Adopting management practices for iris yellow spot based primarily on research conducted on tospoviruses in other crops is further complicated by the limited ability of onion growers to modify cultural practices. For instance, altering planting dates and/or tillage systems and the use of UV-reflective mulches have reduced tomato spotted wilt incidence in several crops. Onion bulb and seed growers in the United States have had limited capacity to adopt these strategies because of the relatively short growing season of the more northern regions of onion production in the United States (necessitating uniform and early planting dates), the small size of onion seed (making limited or no-tillage practices impractical), and dense planting patterns (limiting the usefulness of UV-reflective mulches).
- Management of Iris Yellow Spot and Thrips
- Host resistance to thrips and iris yellow spot. Yield losses in onion crops caused by T. tabaci have been documented for decades, and still occur in most areas of onion production. Similarly, a wide range of yield losses associated with iris yellow spot has been documented in onion bulb and seed crops. Losses resulting from thrips infestations depend on multiple factors, including size
of thrips populations, conduciveness of weather conditions for growth of thrips populations, plant growth stage at the time of infestation, and susceptibility of cultivars to thrips feeding and oviposition damage and/or infection by viruses vectored by thrips. Although this complicates efforts to select for resistance to thrips and/or iris yellow spot in breeding programs, variation in susceptibility or tolerance to thrips among onion cultivars has been documented. Likewise, differences in susceptibility of onion cultivars to iris yellow spot have been reported. These findings highlight the potential role of breeding for resistance/tolerance to thrips damage and IYSV for more effective disease management. Various mechanisms of antixenosis (morphological, physical, or structural plant traits that prevent or inhibit herbivores from finding, colonizing, and accepting the plant) and antibiosis (plant characteristics that prevent or inhibit development or reproduction of herbivores) have been associated with resistance to thrips in onion. Jones et al. reported that a greater angle of divergence of the two innermost leaves and the vertical distance between leaf blades in the sheath column are associated with greater resistance of onion cultivars to thrips. Similar observations were made by Coudriet et al. and Fournier et al.. Presumably, greater openness between the leaves increases thrips exposure to adverse environmental conditions and natural enemies, because thrips seek out narrow spaces on plants, such as leaf sheaths and inflorescences, to live and reproduce. Although some research has indicated that white onion cultivars appear less susceptible to thrips damage than red cultivars, this generalization does not always hold true. Brar et al. screened 61 onion cultivars or breeding lines for resistance to T. tabaci and concluded that susceptibility of onion cultivars was not necessarily correlated with bulb colour. In contrast, a strong correlation was demonstrated between thrips resistance and onion leaf colour. The greater attraction of T. tabaci to blue hues versus green hues suggests that onion cultivars with blue-green foliage may suffer more
damage from thrips feeding than cultivars with green foliage. Cultivars with glossy foliage tend to have a greater degree of
resistance to thrips than cultivars with nonglossy foliage, probably because of differences in chemistry of the leaf waxes or decreased egg-hatching or larval feeding. Al-dosari quantified the tolerance of onion cultivars to onion thrips and found little evidence of differences in T. tabaci host suitability among cultivars (antixenosis and antibiosis resistance mechanisms). However, the cultivars varied widely in their response to onion thrips injury (tolerance resistance mechanism). Some cultivars suffered high losses from thrips, whereas others with similar levels of thrips infestation consistently had little or no yield response from thrips control. It is unclear if increased tolerance to thrips feeding injury will reduce iris yellow spot since tolerant cultivars may have higher
economic-action thresholds for insecticide treatments. Another potential method of minimizing losses to thrips and/or iris yellow spot is to take advantage of klendusity, i.e., the ability of an otherwise susceptible plant or cultivar to escape disease as a result of the
pattern of growth or any mechanical hindrance to infection. For example, early maturing cultivars of onion may escape thrips infestations later in the season. More severe losses to iris yellow spot have been observed in hybrid and open pollinated seed crops in which the parental lines produce tall scapes that lodge more readily during windy conditions than scapes of shorter stature, if large or coalescing iris yellow spot lesions develop on the scapes of both plant types. A negative correlation was demonstrated between seed yield and the incidence of scapes that lodged as a result of iris yellow spot lesions (r = 0.84, P = 0.0093) in an open-pollinated
seed crop with tall scapes. In contrast, very little lodging (< 1%) was observed in a hybrid seed crop with short scapes that displayed a similar incidence of infection (>80% of the scapes infected) to the open-pollinated seed crop. Seed growers located in regions with high risk of iris yellow spot could perhaps plant seed crops of cultivars that produce shorter scapes to reduce the risk of lodging and subsequent seed losses as a result of IYSV infection. Efforts to screen onion cultivars for resistance to iris yellow spot revealed no
cultivar or advanced breeding line that appeared to be immune to IYSV. Complicating efforts to screen for resistance is the difficulty of differentiating resistance to thrips damage from resistance to iris yellow spot, along with inherent differences in yield potential among cultivars. In a 2004 field trial in Washington (USA) in which 46 onion cultivars were evaluated in replicated plots, the incidence of plants with symptoms of iris yellow spot ranged from 58 to 97% for individual cultivars. Similarly, field trials in
Colorado (USA) showed a range in incidence of infected plants from 17 to 100% for 43 cultivars evaluated in 2003, and 14 to 62% for 46 cultivars evaluated in 2004. Significant differences in marketable yield were detected among cultivars in all three trials. In the 2004 trial in Washington (USA), significant negative correlations were detected between incidence of plants with symptoms of iris yellow spot and total marketable yield (r = 0.43 at P = 0.0029) or percentage of jumbo bulbs (r = 0.41 at P = 0.0046).
- Sanitation. Elimination of volunteer onion and planting of transplants free of IYSV and thrips are central to successful management of iris yellow spot in allium production. In Colorado (USA), severe epidemics of iris yellow spot in summer
onion crops sometimes can be traced to infested volunteer onions or contaminated onion transplants. Volunteer onion plants and contaminated transplants are the only sources of primary inoculum identified to date in the High Plains region of the United States, and may provide an important early-season source of inoculum to initiate outbreaks in neighboring onion crops. Interstate movement of infected onion transplants also could facilitate the spread of new strains of IYSV and biotypes of T. tabaci within and among regions of onion production. The importance of weed control in management of iris yellow spot is unknown. Culbreath et al. asserted that for a plant to be an important source of inoculum of TSWV it must:
Based on these conditions, no weeds have been confirmed as important sources of IYSV. However, the known host range of IYSV is increasing steadily, and important reservoirs of the virus in weeds, other crops, and wild Allium species may yet be identified. Therefore, it may be prudent to eliminate from areas of onion cultivation any wild, ornamental, or volunteer plants closely related to i>Allium species, as well as other known hosts of IYSV. Several summer annual weed species have been identified as hosts of IYSV, and these weeds may be important for within-season spread of the virus, or may provide a biological bridge between summer bulb crops and seed or bulb crops planted later in the season and late season winter annual weeds.
- be a host for the
- support reproduction of the vector for at least one generation;
- allow for thrips larvae to acquire the virus;
- be present at a time that complements the disease cycle.
- Crop rotation and isolation. Current understanding of the biology and epidemiology of IYSV and its vector is somewhat limited for development of effective crop rotation and crop isolation strategies. However, some general observations can be considered. The relatively limited host range of IYSV suggests that rotations of host with nonhost crops and spatial isolation of host crops may help limit spread of the virus within a region. Because the biennial season of onion seed crops provides a continuous green bridge for survival of IYSV and its vector through the winter, onion bulb and seed crops should be isolated geographically. Sufficient crop isolation may be critical in regions such as the Pacific Northwest (USA), where biennial seed crops, overwintering bulb crops, and summer bulb crops may be located in the same areas and have growing seasons that overlap by several months. Unfortunately, research on the isolation distances needed to prevent spread of IYSV among host crops is lacking, so current recommendations emphasize maximum separation among fields. Similarly, other hosts (i.e., chive, garlic, leek, and shallot) of
IYSV should not be grown in the vicinity of onion crops.
- Modified cultural practices. Modification of cultural practices may reduce the risk of severe epidemics of iris yellow spot. Consistent with reports of tomato spotted wilt in other cropping systems, increased and more uniform plant density appears to provide some control of iris yellow spot in onion crops. Gent et al. and Fichtner et al. demonstrated a negative relationship of plant population with incidence of plants showing symptoms of iris yellow spot in fields planted to moderately resistant onion cultivars. Plant population sometimes explained greater than 56% of the observed variability in disease incidence. This effect of plant population was not as apparent with more susceptible cultivars, and the significance of planting pattern on development of iris yellow spot remains unclear. In general, there appears to be a relationship between plant stress, predisposition
to damage by thrips, and severity of iris yellow spot, although no studies have quantified the contribution of abiotic and biotic stresses to development of iris yellow spot. A sensible recommendation for pest management and production strategies, where possible, is to reduce stress to the onion crop from moisture extremes, compaction, and soilborne diseases such as pink root (caused by Phoma terrestris) and Fusarium basal rot by (caused Fusarium oxysporum f. sp. cepae). More research is needed on the role of plant stress and predisposition of onion to iris yellow spot.
In preliminary surveys conducted in Colorado and Washington (USA), overhead irrigation has consistently been associated with a reduced incidence and severity of iris yellow spot. However, quantitative estimates of disease suppression provided by overhead irrigation are lacking. Thrips populations often decline in response to heavy rain, and overhead irrigation has been suggested as a
means of suppressing thrips pests in various crops, including onion. The interactions of irrigation, thrips populations, and iris yellow spot may be more complex than simply associated with mortality of thrips caused by overhead irrigation. Yield losses in onion resulting from thrips feeding injury are increased by stress from inadequate water supply, and separating the effects of irrigation
on thrips mortality from alleviation of moisture stress may be difficult. Further studies are warranted to determine the importance of irrigation method and management on suppression of iris yellow spot and onion thrips.
- Thrips management. Onion growers in the western United States rely heavily on insecticides for management of thrips, and
insecticidal management of T. tabaci as an indirect means of controlling iris yellow spot has been an area of study in recent
years (23,52). However, conventional insecticides such as the pyrethroids, organophosphates, and carbamates have become ineffective in some regions of onion production because of development of insensitivity to these insecticides in thrips populations. Research is underway to identify reduced-risk and new insecticides for managing thrips. For example, the insecticides spinosad and neem extract have shown promise for managing thrips in onion crops, based on studies conducted in Colorado and Oregon (USA).
In Colorado in 2004 and 2005, rotating applications of neem extract and spinosad, in combination with straw mulching, reduced thrips numbers compared with a conventional rotation of lamba-cyhalothrin and methomyl, and resulted in an increase in yield of jumbo grade. Mulches have been used to manage insect pests in many cropping systems. Reflective mulches can reduce
thrips populations by disrupting the ability of the thrips to recognize and alight on host plants, and UV-reflective mulches have proven useful in crops such as tomato for reducing thrips populations and development of tomato spotted wilt. Unlike tomato crops, in which entire planting beds can be mulched, applying a UV-reflective mulch to onion beds with multiple rows of plants is not practical, and studies in Colorado (USA) revealed only marginal reductions in thrips populations as a result of reflective mulches applied to the centre of beds planted with two rows of onions. However, straw mulching appears promising for thrips management in onion crops. In studies conducted in Colorado in 2005, straw mulch applied to the centre of onion beds reduced thrips populations by as much as 48% with a corresponding increase in yield of 14% or greater. Although there was no apparent effect of the straw mulch treatment on iris yellow spot in these trials, additional studies are in progress to determine if straw mulching may suppress this disease. The mechanism(s) by which straw mulch suppresses thrips populations is not known, but conservation of natural predators of thrips has been suggested. In field trials in Colorado (USA) in 2004 and 2005, differences in populations of minute pirate bugs
(Orius tristicolor) and predatory thrips were not observed between different mulch types, although differences in light reflectance were detected between nontreated and straw-mulched plots. The mechanism of thrips suppression may also be indirect.
In the absence of thrips pressure, straw mulches applied to irrigation furrows increased onion yields by 64 to 74% due to decreased water runoff and increased lateral movement of soil moisture in mulched plots. Straw mulching may alleviate water stress in hot and dry growing conditions, potentially increasing onion tolerance to thrips feeding and indirectly increasing plant tolerance to iris yellow spot.
- Systemic acquired resistance. Improved management of plant diseases caused by tospoviruses in other cropping systems has been achieved through induction of systemic acquired resistance (SAR), most often through the application of exogenous chemicals such as salicylic acid or its structural analogs. SAR is an induced plant resistance that is first localized to the site of infection, and then spreads systemically to distal non-infected tissues remote from the initial site of infection, triggering a range of defense mechanisms that include formation of phenolics, phytoalexins, callose, pathogenesis-related proteins, and hydroxyproline-rich glycoproteins. Acibenzolar-S-methyl (Actigard, Syngenta Crop Protection, Greensboro, NC, USA) is a structural analog of salicylic
acid in the benzothiadiazole class of SAR inducers. This SAR product has been demonstrated to minimize damage caused by a range of fungal, bacterial, and viral plant pathogens. The potential value of SAR compounds for control of iris yellow spot was demonstrated in a field trial in Colorado (USA), in which a 34% reduction in incidence of plants with symptoms of iris yellow spot was observed, compared with non-treated controls, following four foliar applications of acibenzolar-Smethyl, with a corresponding increase in jumbo grade bulbs. In Florida, applications of acibenzolar-S-methyl reduced the incidence
of tomato plants infected with TSWV by 28% in each of two seasons with high disease pressure, but had no significant effect on TSWV in a season with mild disease pressure. Applications of acibenzolar-S-methyl also reduced numbers of thrips (Frankliniella spp.) in tomato flower on some dates establishing that applications of salicylic acid induce defensive proteins in plants that provide resistance to certain insects, including thrips. Data from field trials suggest acibenzolar-S-methyl may have little effect on thrips populations in onion crops, indicating that the effects of the
product on iris yellow spot are a result of suppression of the virus rather than the vector and/or enhancement of host tolerance to thrips damage or IYSV. Induced resistance involves complex physiological processes that may incur costs to the induced plants expressed as phytotoxicity or reduced yields. Gent and Schwartz documented a 22 to 27% reduction in onion bulb yield when 10
weekly applications of acibenzolar-Smethyl were made in the absence of disease, although this was 2.5 times the maximum number of applications indicated on the Actigard 50WG label for registered crops. Cole (1999) observed mild symptoms of phytotoxicity in tobacco seedlings caused by applications of acibenzolar-S-methyl, but not when the product was applied in the field after transplanting. The phytotoxic effects were overcome by applying a top dressing of calcium nitrate to the seedlings, and Cole suggested diversion of nitrogen or calcium into the SAR initiated metabolism. Further research is needed to determine optimum use of SAR products in onion crops (number, rate, and timing of applications) to maximize control of IYSV and thrips, while minimizing phytotoxic effects. Determining the optimum rate and timing of SAR products is critical for biennial seed crops because of the extended opportunity for IYSV infection during the 14- to 15-month growing season.
- Integrated management of IYSV. Effective long-term management of IYSV in onion crops will depend on a multifaceted approach that integrates host resistance, modified cultural practices, and judicious use of chemical tools. An effective integrated
management program was developed for tomato spotted wilt of tomato by Momol et al. (2004), in which a combination of UV-reflective mulch, applications of acibenzolar-S-methyl, and applications of reduced-risk insecticides that conserve thrips predators was very effective at managing the disease. Tomato growers in northern Florida and southern Georgia (USA) rapidly are adopting these management tools for control of TSWV. Similar efforts are needed to develop economically feasible and practical management options for iris yellow spot and onion thrips in onion crops.
- Outlook and Future Directions
Since the original description of IYSV in 1998, iris yellow spot has become pandemic in regions of onion bulb and seed production. The prolific nature of onion thrips in onion crops, the propensity for thrips to develop insecticide resistance, and the ability of onion thrips to vector IYSV present a serious threat to profitable and sustainable production of onion bulbs and onion seed. However, new knowledge about the biology, epidemiology, and management of iris yellow spot has emerged in a relatively short time, with a significant inventory of research accomplishments. The main vector of IYSV has been identified, insights into the diversity of the
pathogen and its relation to other tospoviruses have been determined, alternate weed and crop hosts continue to be reported,
and inoculum sources of the pathogen and vector have been identified. Moderate levels of disease resistance have been identified in some onion cultivars, and these may be suitable for commercial production and in breeding programs. Biologically based approaches for onion thrips management also have emerged. Additional research should lead to development of new management strategies so that iris yellow spot can be managed economically in both onion bulb and seed crops.
- Short-term research directions. Many basic epidemiological questions on iris yellow spot remain to be addressed. Despite
intensive use of insecticides for control of iris yellow spot, the direct relationship between thrips control and reductions in disease incidence and/or severity have not been reported. A critical evaluation of the relationship of thrips control to disease development is needed to provide growers with sound IPM approaches for iris yellow spot. Although inoculum sources of IYSV have been identified, the relative contributions of these sources of inoculum are unclear. Additional overwintering sources and hosts of IYSV likely will be identified, and other vectors may yet be discovered.
A pressing research need is to develop management strategies for the disease in onion seed crops. The emerging body of knowledge on iris yellow spot has focused largely on onion bulb crops, and our knowledge of the epidemiology and management of the disease in onion seed crops is minimal. Onion seed crops are biennial with approximately a 14-month season from planting in July to harvest the following year. As a result, one seed crop season can overlap with two 5- to 6-month-long seasons of spring-planted bulb crops.
Managing thrips and iris yellow spot over such a long period presents a serious challenge. Additionally, seed growers produce seed crops on a contract basis with seed companies, and generally do not have the choice to select less susceptible parental lines or cultivars. Management tactics developed for bulb crops need to be validated in seed crops, and may require additional measures to provide adequate control of the disease.
- How long do thrips need to feed on infected plants to become viruliferous or to transmit IYSV ?
- What is the transmission efficiency of different populations of T. tabaci, and what does this indicate about key reservoirs of the pathogen ?
- Asymptomatic infections appear to be common in onion bulb and seed crops, but what is the role of such latent infections in development of iris yellow spot epidemics ?
- What is the minimum isolation distance needed between bulb and biennial seed crops, or between onion and other host crops, to prevent dissemination of the virus, and what insights could this provide on inoculum sources and/or vector dispersal ?
- What relationships exist among abiotic and biotic plant stresses, vector reproduction, and disease severity, and can these relationships be quantified ?
- How do host nonpreference, plant architecture, and other thrips tolerance mechanisms impact primary and secondary spread of IYSV ?
- Perhaps most importantly, how successfully can the disease be managed by integration of biological, chemical, and cultural control tactics ?
- Long-term research directions. Longterm management of iris yellow spot likely will depend on development of onion cultivars
with high levels of disease resistance. Incorporating iris yellow spot resistance into an onion genotype with the horticultural traits required by growers and consumers is not a trivial undertaking. Artificial inoculation of IYSV in cultivar screening and breeding trials may allow heritable host resistance to be observed under controlled environmental conditions, but disease symptoms are difficult to produce on onion by mechanical inoculation with IYSV. Therefore, research is needed to isolate the genotypic components of disease resistance/tolerance from the complex interactions of thrips host selection, tolerance, uneven thrips distribution, and inherent differences in vigour and yield among genotypes. If other abiotic or biotic plant stresses are superimposed on these interactions, disentangling cause from effect becomes exceedingly difficult. It is possible to select for individuals with fewer or less severe symptoms of iris yellow spot under field conditions, but it may be unclear if the phenotype is heritable or simply the result of experimental conditions imposed by conditions of that trial. Selection by breeders is difficult because resistant individuals or families must be identified recursively for production of subsequent generations. Consequently, cultivars with high levels of resistance likely will not be available in the next 5 to 10 years. In the interim, growers will have to rely on cultivars with moderate levels of resistance or tolerance to iris yellow spot. One possible approach for developing resistance to IYSV may be through generating transgenic onion lines that express a portion of the IYSV nucleocapsid protein gene. Pathogen-derived resistance has been
used successfully for several diseases caused by tospoviruses, and a transformation system for onion has been developed. High levels of resistance could be introduced into cultivars adapted to specific regions, such as the western United States. However, consumer acceptance of genetically modified foods, especially of a vegetable crop consumed directly, remains challenging. It is unlikely that such resistance will be available commercially in the near future.
Development of ecologically based onion production systems that consider the interactions of multiple pests, horticultural practices, and environmental quality should be a long-term research priority.
Researchers and extension specialists are now addressing these and other questions central to the development of sustainable and profitable management strategies for iris yellow spot and thrips.
- What crop rotation schemes minimize overwintering of the pathogen and vector ?
- Does the type of planting material (i.e., bulbs, seed, or transplants) influence epidemic development ?
- How do other pests respond when planting patterns and populations are modified ?
- What is the economic injury level for thrips when iris yellow spot is a threat, and how does this vary among cultivars ?
- Are insecticides, herbicides, and fungicides used routinely in onion production compatible with biologically based pest management ?
- What cultural and biological tactics can reduce or replace conventional insecticides for thrips management ?
Leek yellow stripe virus (LYSV):
This virus disease is distributed in Asia (Bangladesh, China, Japan, Indonesia, Iran, Thailand, Turkey, Vietnam, and Yemen), in Europe (Belgium, Czech Republic, Denmark, Finland, France, Germany, Greece, Italy, Netherlands, and Sweden), in Oceania (Australia and New Zealand) in North America such Mexico and United States (Oregon, Washington), in South America (Argentina, Brazil, Chile, Colombia, Uruguay, and Venezuela).
- Pest Description
Allium species (garlic, onion, and leek) are grown commercially all over the world for consumption or ornamental decoration. Leek yellow stripe virus (LYSV) is the causal agent of yellow stripe disease in leek and mosaic disease in garlic. Severe epidemics of yellow stripe disease on leek in Germany in the 1950, and twenty years later in the Netherlands catalyzed more intensive research into the viral causal agent of the disease. These investigations proved difficult, as the causal agents of yellow striping occurred in virus complexes that were challenging to characterize. The first official report of LYSV in commercial garlic was in 1987, but later investigations demonstrated the presence of the virus in New Zealand as early as 1981.
The virus is a positive-sense single stranded RNA virus that houses its genetic material in a non-enveloped capsid (Davis, 2008a). The virus particles are flexuous (rod-like and bendable) particles 815 to 820 nm long that aggregate end-to-end. The protein coat of the virus is 34 kDa with a buoyant density in a cesium chloride gradient of 1.326 g/cm3.
- Biology and Ecology
Leek Yellow Stripe Virus is a potyvirus specific to Allium species. The Allium potyviruses rarely cross over to infect new hosts, which eases the threat of contamination and spread to neighboring non-Allium hosts. LYSV is commonly found in nature in viral complexes with other Allium potyviruses and carlaviruses, such as onion dwarf yellow virus (ODYV) and garlic common latent virus (GCLV). The appearance of LYSV in these viral complexes made initial identification and classification difficult. Symptom expression is rare and haphazard in the field during summer months, but becomes increasingly apparent in the fall months. Autumn and winter crops can be completely infected. In the late 1970s, there was a shift from lighter-coloured cultivars to darker-coloured, less sensitive cultivars in commercial production. This led to a decrease in the incidence of LYSV in autumn crops. This apparent resistance has been credited to the thicker cuticular wax layer on the darker leek cultivars (Vandijk, 1993).
- Symptoms and Signs
In garlic, LYSV causes light yellow striping on the distal part the leaves, which can lead to dwarfing of the entire plant. The virus also causes bulbs to be smaller and malformed, which results in yield loss. In leek, LYSV causes irregular yellow striping on the leaves, particularly near the base, but not confined to this area. In certain instances, entire leaves can turn yellow. Diseased plants are drier with soft, limp, and/or deformed leaves. Symptoms observed in the field could be replicated in the greenhouse, and usually appeared within 14 days of inoculation. Allium crops infected with LYSV are more susceptible to weather conditions like frost, and do not keep well post-harvest.
- Pest Importance
Potyviruses rarely infect in isolation, and complexes of different strains and species are common. Infections of LYSV in the field can be devastating, sometimes approaching 100% on leek plots (Bos, 1983). Yield loss in garlic bulbs can approach 60% and climb to 84% when doubly infected with another potyvirus. Germination rate in garlic is also affected and can decline to 60% of normal when doubly infected with another potyvirus. Garlic exports in the United States were valued at approximately $ 8.8 million in 2008, and world-wide production was valued at $ 187 million. Significant losses are a possibility if the disease becomes widely established in the United States (NPAG, 2009).
- Known Hosts
- Major hosts: Allium ampeloprasum var. holmense (great-headed garlic), A. ampeloprasum var. porrum (leek), A. ampeloprasum var. sectivum (pearl onion), A. longicupis (wild garlic), and A. sativum (garlic).
- Minor hosts: Allium cepa var. cepa (onion) and A. cepa var. ascalonicum (shallot) (Bos, 1981; Vandijk, 1993).
- Experimental/Indicator Hosts: Chenopodium amaranticolor (tree spinach), C. quinoa (quinoa), and Celosia argentea (silver cocks comb) (Bos, 1981; Vandijk, 1993).
- Known vectors (or associated organisms)
Common aphid vectors of LYSV are the green peach aphid (Myzus persicae) and the black bean aphid (Aphis fabae). Both species are found on every continent except Antarctica, and in over half of the 50 United States (CIE, 1963). These aphids are mono- or polyphagous depending on the growth stage. The youngest stages have a single primary host during the winter and spread to other hosts in the summer months as the nymphs grow. They both spread numerous plant viruses in addition to LYSV in a non-persistent manner during feeding (Blackman and Eastop, 2000).
Other aphids used to experimentally inoculate host plants include: Rhopalosiphum maidis (corn aphid, corn leaf aphid), R. padi (bird cherry oat aphid), Schizaphis graminum (greenbug), Aphis gossypii (melon aphid, cotton aphid) , A. nerii (oleander aphid), Uroleucon sonchi (sowthistle aphid), and Hyperomyzus carduellinus (Asian sowthistle aphid) (Lunello et al., 2002).
LYSV is also commonly associated with other Allium viruses, i.e., it has a synergistic relationship with onion dwarf virus (ODV). Multiple investigations have demonstrated that plants express aggravated symptoms when infected with LYSV and one or more other viruses (Vandijk, 1993; Lot et al., 1998). Reverse transcriptase polymerase chain reaction (RT-PCR) and immunocapture reverse transcriptase polymerase chain reaction (IC-RT-PCR) methods are available to distinguish LYSV from onion yellow dwarf virus (ODV) in single and mixed infections (Dovas et al., 2001; Lunello et al., 2005).
the United States.
LYSV can spread locally through aphid vectors (M. persicae, A. fabae) in a non-persistent manner, meaning that the virus does not replicate in the host, and stays localized on the piercing stylet of the aphid. During feeding, the stylet breaks through plant tissue, and deposits the virus. Typically however, aphid vectors move the virus into the plot too late in the growing season to cause economic losses in that same season (Davis, 2008). Propagative plant material is the most important long-distance transmission pathway, since the United States allows peeled garlic cloves from all countries without a permit imports Allium sp. for propagation from a wide variety of countries, including Mexico (NPAG, 2009). The virus can also be transmitted in sap inoculation, a common practice in experimental settings.
- CAPS-Approved Method. The CAPS-approved survey method is to collect symptomatic plant tissue by visual survey. Survey Sample Collection: leaves (remove leaf tip samples from the second youngest leaf on symptomatic plants); bulbs (remove bulb from the symptomatic plants of interest).
- Literature-Based Methods. In areas where the disease is known to occur it is recommended that at least 100 leaf samples (not necessarily symptomatic) per crop be collected if possible (Smith et al., 2006). From bulbs, remove one clove from the bulb, and cut a cube of approx. 1.0 x 0.5 x 0.5 cm from the basal region (Conci et al., 2002). The leaf tip and bulb cubes samples should be used in diagnostic analysis.
- Key Diagnostics/Identification
- CAPS-Approved Method. Enzyme Linked Immunosorbent Assay (ELISA): Agdia and AC diagnostics have commercially available double antibody sandwich (DAS) ELISAs for LYSV available using polyclonal antisera.Neither of the commercial ELISA tests have been validated for regulatory purposes at this time, however. This test is to be used for screening only. Positive results will need to be verified using molecular methods.
- Literature-Based Methods.Indicator Hosts: 1) Allium porrum (yellow leaf stripes are observed with infection of LYSV); 2) Chenopodium amaranticolor and C. quinoa: (diagnostic symptoms of LYSV include chlorotic local lesions that become green rings when leaves senesce); 3) Celosia argentea (brown necrotic local lesions are observed with infection of LYSV).
- ELISA. From the affected plant extrated sap was tested for LYSV with general potyvirus monoclonal antibodies from Agdia Inc. (Elkhart, Indiana). They also used an ELISA with polyclonal antibodies (not known to be commercially available). The authors measured optical density of the ELISA plates at 405 nm. Positive readings are defined as any sample with an A405 of at least three times the mean of the negative control. Use healthy sap of non-host plants as the negative control. This diagnostic should be verified with RT-PCR or sequencing to confirm it is LYSV and not another potyvirus.
- Immunoelectromicroscopy. Virus particles are trapped from crude leaf extracts on copper grids in 0.1 M phosphate buffer at pH 7.0 for 15 minutes. Grids are washed with 1:50 dilution of LSYV antiserum for 15 minutes. Decorated virus particles are then stained with 1% (weight/volume) of uranyl acetate (Dovas et al., 2001).
- Molecular. RT-PCR: RT-PCR was performed using specific primers designed from the consensus regions of the coat protein genes of Leek yellow stripe virus (Fajardo et al., 2001). Viral RNA is extracted from purified virus samples or total RNA from infected plants. The cDNA is synthesized from the RNA using a Time Saver cDNA Synthesis Kit (Pharmacia Biotech). To amplify viral cDNA, add 10 μL of the RT reaction to 50 μl polymerase reaction mixture containing 20 mM Tris-HCl, pH 8.4, 50 mM KCl, 1.5 mM MgCl2, 200 μM each dNTPs, 2.5 U of Taq DNA polymerase and 100 ng each of 1LYSV (5 TCA CTG CAT ATG CGC ACC AT 3) and 2LYSV (5 GCA CCA TAC AGT GAA TTG AG 3). Run the reaction in a PCR protocol of 94 °C for 5 min, followed by 35 cycles (94 °C/1 min, 50 °C/2 min and 72 °C/2 min) and a final amplification at 72 °C for 7 min. The expected fragment is approximately 1000 base pairs. Pappu et al. (2008) also provide specific details on RT-PCR and primers for Leek Yellow Stripe Virus.
- Easily Confused Species. Leek Yellow Stripe Virus could be confused with Iris Yellow Spot Virus (IYSV) depending on the expression of symptoms (Pappu et al., 2005). Both of these viruses infect leek, but IYSV is a tospovirus, not a potyvirus. The main hosts of IYSV are onion and shallot, but the virus has the capacity to infect leek as well (Smith et al., 2006). IYSV is not known to infect any variety of garlic.
IYSV also causes chlorotic (yellow) lesions on unfurled leaves, but the lesions are distinctly diamond-shaped instead of continuous down the lamina as with LYSV (Schwartz et al., 2002). Iris yellow spot virus typically only infects leaves, compared to LYSV which infects bulb tissue with ease. IYSV is also established in many states, and is not considered an exotic pest (Smith et al., 2006).
IYSV vector transmission also differs from LYSV. Iris yellow spot virus is vectored by the onion thrips (Thrips tabaci) larvae in a persistent and propagative manner, meaning that the virus passes into the insects salivary glands, and multiplies inside the vector. Transmission of IYSV therefore depends on the life stage of the vector and the success of replication inside that vector (Kritzman et al., 2001; Srinivasan et al., 2012). Another easily confused virus is Onion Yellow Dwarf Virus (OYDV). OYDV is also a potyvirus with similar symptoms to LYSV. Like LYSV, streaking starts at the base of the leaf and can spread to complete yellowing of the entire leaf. Leaves are sometimes flattened and fall over often. OYDV is transmitted by the same two species of aphids and via vegetative propagation, and is often found in complex with LYSV. The OYDV virus forms thread-like particles about 722 to 820 nm long (Davis, 2008). To distinguish which virus is present in a symptomatic plant, it is best to use molecular diagnostics.
Garlic common latent carlavirus (GCLV):
Host range and symptoms
- Synonyms: Garlic Latent Virus - France (Delacolle and Lot, 1981; Germany (Graichen and Leistner, 1987).
- Acronyms: GCLV, GLV
- ICTV decimal code: 18.104.22.168.010
First reported on Allium sativum (garlic), A. ampeloprasum var. holmense (great headed garlic), A. porrum (leek). From the Netherlands by Van Dijk (1993). On these species no obvious symptoms were observed.
Virus transmitted by mechanical inoculation.
Probably distributed worldwide. Spreads in Argentina, the former Czechoslovakia, France, Germany, Israel, Japan, and the UK.
Diagnostically susceptible host species and symptoms
Diagnostically insusceptible host species
Maintenance and propagation hosts
- Celosia argentea on that are obsterved chlorotic and/or necrotic local lesions; no systemic infection.
- Chenopodium amaranticolor with faint green local rings; no systemic infection.
- Chenopodium murale, C. quinoa with chlorotic etched local lesions; no systemic infection.
- Nicotiana occidentalis where there are no local symptoms, systemic vein necrosis.
- Allium porrum,
- Nicotiana occidentalis
Susceptible host species
- Chenopodium murale (Local lesions),
- Chenopodium quinoa (Local lesions),
- Allium porrum (Whole plants).
Insusceptible host species
Families containing susceptible hosts
- Allium ampeloprasum var. holmense
- Allium porrum
- Allium sativum
- Celosia argentea
- Chenopodium amaranticolor
- Chenopodium murale
- Chenopodium quinoa
- Nicotiana occidentalis
Families containing insusceptible hosts
- Alliaceae (3/3)
- Amaranthaceae (1/1)
- Chenopodiaceae (3/3)
- Solanaceae (1/1)
Physical and biochemical properties
- Leguminosae-Papilionoideae (1/1)
Taxonomy and relationships
- Particle morphology
- Virions filamentous of 650 nm.
- Sequence database accession codes
- D11161 Em(40)_vi:GCVRRCP1 Gb(84)_vi:GCVRRCP Garlic mosaic virus genes for RNA replicase and coat protein. 10/92 3,459bp.
- X67134 Em(40)_vi:GMVRNA Gb(84)_vi:GMVRNA Garlic mosaic virus genomic RNA. 7/92 1,972bp. 2 sequences.
- X67135 Em(44)_pl:Asmrnglv Gb(90)_pl:Asmrnglv A.sativum mRNA for Garlic Latent Virus. 9/93 2,145bp.
- Viruses with serologically unrelated virions
- Shallot latent virus (SLV).
Onion yellow dwarf virus (OYDV):
Garlic is vegetatively propagated, and all traditional commercial clones can be infected with one o more viruses. Some viruses, such as the potyvirus onion yellow dwarf virus (OYDV) and leek yellow streak virus (LYSV) cause mosaic symptoms in infected leaves and can cause yield reductions in excess of 25%. Other viruses, mainly carla- and rymoviruses, are latent in the leaves and cloves, and do not appear yield significantly.
Infected leaves have symptoms ranging from yellow streaks to complete yellowing. Leaves tend to flatten, crinkle, twist and bend over. Plants may be wilted and dwarfed and bulbs usually remain solid but do not reach their full size. In seed crops, plants produce smaller flower clusters and fewer florets.
- Conditions for disease development
The virus is carried by infected seed bulbs, onion sets and volunteer onions. Many aphid species can transmit this virus from infected to healthy plants. Plants that are infected at a young stage may form small bulbs or fail to form bulbs, whereas plants infected during mid-season may produce slightly undersized bulbs.
Some garlic varieties are tolerant and can help reduce losses from this disease. In our experiments, cv Baladi and cv Seds 40 showed 45.4% (64/141 of infected/tested bulbs of garlic) and 59.2% (84/142), respectively, of OYDV presence in bulbs, by using DAS-ELISA test (Fiume, 2009). The use of true seed for garlic production results in virus-free plants since the virus is not seed-borne. The use of virus-free bulbs and sets, and producing crops in an area where the virus is absent are also effective. Roguing out infected plants helps to reduce the incidence of this virus. Stage may form small bulbs or fail to form bulbs, whereas plants infected during mid-season may produce slightly undersized bulbs.
Many species of aphids
Mosca della cipolla e dellaglio
Nome scientifico: Delia antiqua Meigen, 1826
- Inquadramento sistematico di Delia antiqua
Specie: Delia antiqua
Il danno è provocato dal dittero antomide Delia antiqua il cui adulto (circa 6-7 mm di lunghezza) ha il corpo di colore grigio-nerastro. La larva, apoda e giallognola, presenta il corpo che si restringe verso lestremità cefalica. La Mosca della cipolla infesta i bulbi distruggendone i tessuti di cui si nutre; inoltre i bulbi infestati vengono invasi da batteri che ne determinano la decomposizione.
La Delia antiqua sverna come pupa, nel terreno. Allinizio della primavera sfarfallano gli adulti; le femmine, dopo laccoppiamento, depongono le uova sui bulbi ed alla base delle piante. Da queste uova, dopo circa una settimana, fuoriescono le larve che penetrano allinterno del bulbo, dove rimangono fino al raggiungimento della maturità; questa viene raggiunta in un arco di tempo che varia da 3 a 6 settimane, a seconda delle temperature ambientali. Raggiunta la maturità le larve abbandonano il bulbo, per andare ad impuparsi nel terreno. Nellarco dellanno si possono compiere anche 3-4 generazioni, per cui linsetto, nei climi più miti, può rimanere in campo anche nellautunno inoltrato. Inoltre, i bulbi una volta infestati vengono attaccati da batteri che determinano la morte della pianta.
La lotta contro la Mosca della cipolla e di tipo agronomico e di tipo chimico. La lotta agronomica consiste essenzialmente nellattuazione di semine posticipate, per evitare i danni della 1a generazione che è la più pericolosa. La lotta chimica può essere di tipo preventivo e consiste nella disinfezione del terreno, specialmente nelle zone dove la presenza del fitofago è costante. Inoltre, si può attuare una lotta chimica anche con colture in atto; in questo caso si interviene o sugli adulti in fase di sfarfallamento o sugli stadi giovanili originati.
Mosca (Suillia univitata)
Interventi specifici:- catture con attrattivi alimentari degli adulti svernanti.
Nome scientifico: Dyspessa ulula Borkhausen, 1790
- Inquadramento sistematico di Dyspessa ulula
Specie: Dyspessa ulula
E un lepidottero della famiglia dei Cossidae, le cui larve attaccano i bulbi in campo attraverso una galleria che riempiono di escrementi durante la fase di maturazione e quando l'infestazione è più grave svuotano buona parte dei bulbi. Lattività delle larve continua in magazzino passando da un bulbo allaltro, riuscendo a causare notevoli danni. Gli adulti sfarfallano dalla metà di giugno a metà luglio, si accoppiano e depongono le uova alla base delle piante. Le larve penetrano nei bulbi praticando un foro nelle tuniche e scavando una galleria completano lo sviluppo dopo circa 40 giorni, si incrisalidano nelle anfrattuosita dei magazzini o nel terreno per poi sfarfallare in primavera.
La difesa è basata su misure agronomiche consistenti nella distruzione dei bulbi infestati al momento della raccolta e immagazzinando separatamente la produzione sospetta o lievemente infestata.
Dei buoni risultati sono stati ottenuti con Spinosad, intervenendo, al massimo, una volta allanno,
oppure con Etofenprox al massimo 1 intervento all'anno che è efficace anche contro la mosca.
Garlic is widely used around the world for its pungent flavour as a seasoning or condiment. It is a fundamental component in many or most dishes of various regions, including eastern Asia, south Asia, Southeast Asia, the Middle East, northern Africa, southern Europe, and parts of South and Central America.
The flavour varies in intensity and aroma with the different cooking methods (figure 21). It is often paired with onion, tomato, or ginger. The parchment-like skin is much like the skin of an onion and is typically removed before using in raw or cooked form. An alternative is to cut the top off the bulb, coat the cloves by dribbling olive oil (or other oil-based seasoning) over them, and roast them in an oven.
Garlic softens and can be extracted from the cloves by squeezing the end of the bulb (root), or individually by squeezing one end of the clove. In Korea, heads of garlic are fermented at high temperature; the resulting product, called black garlic, is sweet and syrupy, and is now being sold in the United States, United Kingdom and Australia.
Garlic may be applied to breads to create a variety of classic dishes such as garlic bread (bread topped with garlic and olive oil or butter, figure 22), garlic toast, bruschetta, crostini and canapé (figure 23).
Figure 21 Garlic being crushed using a garlic press.
Figure 22 Bread topped with garlic and olive oil or butter.
Figure 23 Garlic being rubbed onto slice of bread.
Oils can be flavoured with garlic cloves. These infused oils are used to season all categories of vegetables, meats, breads and pasta.
In some cuisine, the young bulbs are pickled for 36 weeks in a mixture of sugar, salt, and spices. In eastern Europe, the shoots are pickled and eaten as an appetizer.
Immature scapes are tender and edible. They are also known as "garlic spears", "stems", or "tops". Scapes generally have a milder taste than the cloves. They are often used in stir frying or braised like asparagus. Garlic leaves are a popular vegetable in many parts of Asia. The leaves are cut, cleaned, and then stir-fried with eggs, meat, or vegetables.
Mixing garlic with egg yolks and olive oil produces aioli (garlic mayonnaise). Garlic, oil, and a chunky base produce skordalia. Skordalia is a thick puree (or sauce, dip, spread, etc.) in Greek cuisine made by combining crushed garlic with a bulky base - which may be a purée of potatoes, walnuts, almonds, or liquid-soaked stale bread - and then beating in olive oil to make a smooth emulsion.
Blending garlic, almond, oil, and soaked bread produces ajoblanco. The ajoblanco is a popular Spanish cold soup typical from Granada and Málaga (Andalusia). It is also a common dish in Extremadura (Ajo Blanco Extremeño). This dish is made of bread, crushed almonds, garlic, water, olive oil, salt and sometimes vinegar. It is usually served with grapes or slices of melon
Garlic powder has a different taste from fresh garlic. If used as a substitute for fresh garlic, 1/8 teaspoon of garlic powder is equivalent to one clove of garlic.
Domestically, garlic is stored warm (above 18 °C) and dry to keep it dormant (so that it does not sprout). It is traditionally hung; softneck varieties are often braided in strands, called "plaits" or grappes. Garlic is often kept in oil to produce flavoured oil; however, the practice requires measures to be taken to prevent the garlic from spoiling. Untreated garlic kept in oil can support the growth of deadly Clostridium botulinum. Refrigeration will not assure the safety of garlic kept in oil. Peeled cloves may be stored in wine or vinegar in the refrigerator.
Commercially prepared oils are widely available, but when preparing and storing garlic-infused oil at home, there is a risk of botulism if the product is not stored properly. To reduce this risk, the oil should be refrigerated and used within one week. Manufacturers add acids and/or other chemicals to eliminate the risk of botulism in their products. Two outbreaks of botulism related to garlic stored in oil have been reported.
Commercially, garlic is stored at 0 °C, in a dry, low humidity environment. Garlic will keep longer if the tops remain attached.
Ready peeled garlic cloves sold in a plastic container (figure 24).
Figure 24 Ready peeled garlic cloves sold in a plastic container.
Garlic has been used as both food and medicine in many cultures for thousands of years, dating at least as far back as the time that the Giza pyramids were built. Garlic is still grown in Egypt, but the Syrian variety is the kind most esteemed now.
Garlic is mentioned in the Bible and the Talmud. Hippocrates, Galen, Pliny the Elder, and Dioscorides all mention the use of garlic for many conditions, including parasites, respiratory problems, poor digestion, and low energy. Its use in China was first mentioned in A.D. 510.
It was consumed by ancient Greek and Roman soldiers, sailors, and rural classes (Virgil, Ecologues ii. 11), and, according to Pliny the Elder (Natural History xix. 32), by the African peasantry. Galen eulogizes it as the "rustic's theriac" (see F. Adams' Paulus Aegineta, p. 99), and Alexander Neckam, a writer of the 12th century (see Wright's edition of his works, p. 473, 1863), recommends it as a palliative for the heat of the sun in field labour.
In the account of Korea's establishment as a nation, gods were said to have given mortal women with bear and tiger temperaments an immortal's black garlic before mating with them.
This is a genetically unique six-clove garlic that was to have given the women supernatural powers and immortality. This garlic is still cultivated in a few mountain areas today.
In his Natural History, Pliny gives an exceedingly long list of scenarios in which it was considered beneficial (N.H. xx. 23). Dr. T. Sydenham valued it as an application in confluent smallpox, and, says Cullen (Mat. Med. ii. p. 174, 1789), found some dropsies cured by it alone. Early in the 20th century, it was sometimes used in the treatment of pulmonary tuberculosis or phthisis. dropsies
Garlic was rare in traditional English cuisine (though it is said to have been grown in England before 1548) and has been a much more common ingredient in Mediterranean Europe. Garlic was placed by the ancient Greeks on the piles of stones at crossroads, as a supper for Hecate (Theophrastus, Characters, The Superstitious Man). A similar practice of hanging garlic, lemon and red chilli at the door or in a shop to ward off potential evil is still very common in India.
According to Pliny, garlic and onions were invoked as deities by the Egyptians at the taking of oaths. Pliny also states that garlic demagnetizes lodestones, which is not factual.
The inhabitants of Pelusium, in lower Egypt (who worshiped the onion), are said to have had an aversion to both onions and garlic as food.
To prevent the plant from running to leaf, Pliny (N.H. xix. 34) advised bending the stalk downward and covering with earth; seeding, he observes, may be prevented by twisting the stalk (by "seeding", he most likely meant the development of small, less potent bulbs).
Medicinal use and health benefits
In test tube studies, garlic has been found to have antibacterial, antiviral, and antifungal activity. However, these actions are less clear in humans. Garlic is also claimed to help prevent heart disease (including atherosclerosis, high cholesterol, and high blood pressure) and cancer.
Garlic is used to prevent certain types of cancer, including stomach and colon cancers. In fact, countries where garlic is consumed in higher amounts, because of traditional cuisine, have been found to have a lower prevalence of cancer.
Animal studies, and some early investigational studies in humans, have suggested possible cardiovascular benefits of garlic. A Czech study found that garlic supplementation reduced accumulation of cholesterol on the vascular walls of animals.
Another study had similar results, with garlic supplementation significantly reducing aortic plaque deposits of cholesterol-fed rabbits. Another study showed that supplementation with garlic extract inhibited vascular calcification in human patients with high blood cholesterol.
The known vasodilative effect of garlic is possibly caused by catabolism of garlic-derived polysulfides to hydrogen sulphide in red blood cells, a reaction that is dependent on reduced thiols in or on the RBC membrane. Hydrogen sulphide is an endogenous cardioprotective vascular cell-signaling molecule.
Although these studies showed protective vascular changes in garlic-fed subjects, a randomized clinical trial funded by the National Institutes of Health (NIH) in the United States and published in the Archives of Internal Medicine in 2007 found that the consumption of garlic in any form did not reduce blood cholesterol levels in patients with moderately high baseline cholesterol levels.
According to the Heart.org, "despite decades of research suggesting that garlic can improve cholesterol profiles, a new NIH-funded trial found absolutely no effects of raw garlic or garlic supplements on LDL, HDL, or triglycerides... The findings underscore the hazards of meta-analyses made up of small, flawed studies and the value of rigorously studying popular herbal remedies."
In 2007, the BBC reported that Allium sativum may have other beneficial properties, such as preventing and fighting the common cold. This assertion has the backing of long tradition in herbal medicine, which has used garlic for hoarseness and coughs. The Cherokee also used it as an expectorant for coughs and croup.
Allium sativum has been found to reduce platelet aggregation and hyperlipidemia.
Garlic is also alleged to help regulate blood sugar levels. Regular and prolonged use of therapeutic amounts of aged garlic extracts lower blood homocysteine levels and has shown to prevent some complications of diabetes mellitus. People taking insulin should not consume medicinal amounts of garlic without consulting a physician.
In 1858, Louis Pasteur observed garlic's antibacterial activity, and it was used as an antiseptic to prevent gangrene during World War I and World War II. More recently, it has been found from a clinical trial that a mouthwash containing 2.5% fresh garlic shows good antimicrobial activity, although the majority of the participants reported an unpleasant taste and halitosis.
Garlic cloves are used as a remedy for infections (especially chest problems), digestive disorders, and fungal infections such as thrush.
Garlic has been found to enhance thiamine absorption and therefore reduce the likelihood for developing the thiamine deficiency beriberi.
In 1924, it was found that garlic is an effective way to prevent scurvy, because of its high vitamin C content.
Garlic has been used reasonably successfully in AIDS patients to treat cryptosporidium in an uncontrolled study in China. It has also been used by at least one AIDS patient to treat toxoplasmosis, another protozoa disease.
Garlic supplementation in rats, along with a high protein diet, has been shown to boost testosterone levels.
A 2010 double-blind, parallel, randomised, placebo-controlled trial involving 50 patients whose routine clinical records in general practice documented treated but uncontrolled hypertension. Concluded that "Our trial suggests that aged garlic extract is superior to placebo in lowering systolic blood pressure similarly to current first line medications in patients with treated but uncontrolled hypertension."
Adverse effects and toxicology
Garlic is known for causing halitosis as well as causing sweat to have a pungent 'garlicky' smell which is caused by allyl methyl sulphide (AMS). AMS is a gas which is absorbed into the blood during the metabolism of garlic; from the blood it travels to the lungs (and from there to the mouth causing bad breath) and skin where it is exuded through skin pores. Washing the skin with soap is only a partial and imperfect solution to the smell. Studies have shown that sipping milk at the same time as consuming garlic can significantly neutralize bad breath. Mixing garlic with milk in the mouth before swallowing reduced the odour better than drinking milk afterward. Plain water, mushrooms and basil may also reduce the odour; the mix of fat and water found in milk, however, was the most effective.
Raw garlic is more potent; cooking garlic reduces the effect. The green dry 'folds' in the centre of the garlic clove are especially pungent. The sulphur compound allicin, produced by crushing or chewing fresh garlic produces other sulphur compounds: ajoene, allyl sulphides, and vinyldithiins.
Aged garlic lacks allicin, but may have some activity due to the presence of S-allylcysteine.
In a rat study, allicin was found to be an activator of TRPA1. The neurons released neurotransmitters in the spinal cord to generate pain signals and released neuropeptides at the site of sensory nerve activation, resulting in vasodilatation as well as inflammation. Allicin is released only by crushing or chewing raw garlic and cannot be formed from cooked garlic.
Some people suffer from allergies to garlic and other plants in the allium family. Symptoms can include irritable bowel, diarrhea, mouth and throat ulcerations, nausea, breathing difficulties, and in rare cases anaphylaxis. Garlic-sensitive patients show positive tests to diallyl disulfide, allylpropyldisulfide, allylmercaptan and allicin, all of which are present in garlic. People who suffer from garlic allergies will often be sensitive to many plants in the lily family (Liliaceae), including onions, garlic, chives, leeks, shallots, garden lilies, ginger, and bananas.
Garlic can also cause indigestion, nausea, vomiting, and diarrhea. It thins the blood (as does aspirin); this had caused very high quantities of garlic and garlic supplements to be linked with an increased risk of bleeding, particularly during pregnancy and after surgery and childbirth, although culinary quantities are safe for consumption. There have been several reports of serious burns resulting from garlic being applied topically for various purposes, including naturopathic uses and acne treatment, so care must be taken to test a small area of skin using a very low concentration of garlic.On the basis of numerous reports of such burns, including burns to children, topical use of raw garlic, as well as insertion of raw garlic into body cavities, is discouraged. In particular, topical application of raw garlic to young children is not advisable. The side effects of long-term garlic supplementation, if any exist, are largely unknown, and no FDA-approved study has been performed. However, garlic has been consumed for several thousand years without any adverse long-term effects, suggesting that modest quantities of garlic pose, at worst, minimal risks to normal individuals. Possible side effects include gastrointestinal discomfort, sweating, dizziness, allergic reactions, bleeding, and menstrual irregularities. The safety of garlic supplements had not been determined for children.; some breastfeeding mothers have found their babies slow to feed and have noted a garlic odour coming from their baby when they have consumed garlic.
Garlic may interact with warfarin (an blod anticoagulant, antiplatelets ) (antiaggregant of blood), saquinavir (antiretroviral), antihypertensives, calcium channel blockers, and hypoglycemic drugs, as well as other medications. Members of the allium family might be toxic to cats or dogs.
Some degree of liver toxicity has been demonstrated in rats, particularly in extremely large quantities exceeding those that a rat would consume under normal situations.
When crushed, Allium sativum yields allicin, an antibiotic and antifungal compound (phytoncide, that are antimicrobial allelochemic volatile organic compounds derived from plants). It has been claimed that it can be used as a home remedy to help speed recovery from strep throat or other minor ailments because of its antibiotic properties. It also contains the sulphur containing compounds such as alliin, ajoene, diallylsulfide, dithiin, S-allylcysteine, and enzymes, vitamin B, proteins, minerals, saponins, flavonoids, and maillard reaction products, which are non-sulphur containing compounds.
Furthermore a phytoalexin called allixi was found, a non-sulphur compound with a γ-pyrone skeleton structure with anti-oxidative effects, anti-microbial effects, anti-tumor promoting effects, inhibition of aflatoxin B2 DNA binding, and neurotrophic effects.
Allixin showed an anti-tumor promoting effect in vivo, inhibiting skin tumor formation by TPA and DMBA initiated mice. Analogs of this compound have exhibited anti tumor promoting effects in in vitro experimental conditions. Herein, allixin and/or its analogs may be expected useful compounds for cancer prevention or chemotherapy agents for other diseases.
The composition of the bulbs is approximately 84.09% water, 13.38% organic matter, and 1.53% inorganic matter, while the leaves are 87.14% water, 11.27% organic matter, and 1.59% inorganic matter.
The phytochemicals responsible for the sharp flavour of garlic are produced when the plant's cells are damaged. When a cell is broken by chopping, chewing, or crushing, enzymes stored in cell vacuoles trigger the breakdown of several sulphur-containing compounds stored in the cell fluids. The resultant compounds are responsible for the sharp or hot taste and strong smell of garlic. Some of the compounds are unstable and continue to evolve over time. Among the members of the onion family, garlic has by far the highest concentrations of initial reaction products, making garlic much more potent than onions, shallots, or leeks. Although many humans enjoy the taste of garlic, these compounds are believed to have evolved as a defensive mechanism, deterring animals like birds, insects, and worms from eating the plant.
A large number of sulphur compounds contribute to the smell and taste of garlic. Diallyl disulfide is believed to be an important odour component. Allicin has been found to be the compound most responsible for the "hot" sensation of raw garlic. This chemical opens thermoTRP (transient receptor potential) channels that are responsible for the burning sense of heat in foods. The process of cooking garlic removes allicin, thus mellowing its spiciness.
Because of its strong odour, garlic is sometimes called the "stinking rose". When eaten in quantity, garlic may be strongly evident in the diner's sweat and breath the following day. This is because garlic's strong-smelling sulphur compounds are metabolized, forming allyl methyl sulphide. Allyl methyl sulphide (AMS) cannot be digested and is passed into the blood. It is carried to the lungs and the skin, where it is excreted. Since digestion takes several hours, and release of AMS several hours more, the effect of eating garlic may be present for a long time.
This well-known phenomenon of "garlic breath" is alleged to be alleviated by eating fresh parsley. The herb is, therefore, included in many garlic recipes, such as pistou (or just pistou, is a cold sauce made from cloves of garlic, fresh basil, and olive oil), persillade (a sauce or seasoning mixture of parsley chopped together with seasonings including garlic, herbs, oil, and vinegar), and the garlic butter spread used in garlic bread (figure 13). However, since the odour results mainly from digestive processes placing compounds such as AMS in the blood, and AMS is then released through the lungs over the course of many hours, eating parsley provides only a temporary masking. One way of accelerating the release of AMS from the body is the use of a sauna.
Because of the AMS in the bloodstream, it is believed by some to act as a mosquito repellent.
However, there is no evidence to suggest that garlic is actually effective for this purpose.
Community rules for the quality of garlic (CEE rule n. 2288/97)
- Definition of products
This standard rule is applied to garlic varieties (cultivars) grown from the species Allium sativum L. for fresh or semi-dry or dry use, with the exception of the green garlic with leaves and still without cloves destinated to industrial processing.
Fresh garlic means to produce an harvest with a green stem and the outer tunics of the
bulbs still fresh.
Semi-dry garlic means to harvest with the stem and the outer tunics of the bulbs not completely dry.
Dry garlic means produce a garlic with the stem, the outer tunics of the bulbs, as well as
the tunic surrounding each clove completely dry.
- Quality features
The standard is intended to define the quality requirements of garlic after conditioning
- Minimum requirements
In all classes, subject to the special provisions for each class and the
tolerances allowed, the bulbs must be:
- Healthy, without bulbs affected by rotting or deterioration such as to make it unfit for consumption;
- Practically free from pests,
- Practically free from damage caused by pests;
- Clean, practically free of any visible foreign matter;
- Free from damage caused by frost or sun,
- Free from externally visible sprouts
- Free of abnormal external moisture,
- Free of foreign smell and/or taste (this provision does not preclude smell and taste specific for the smoked garlic).
The development and condition of the garlic must be such as to enable them:
- The transport and handling;
- To arrive in satisfactory conditions at the place of destination.
The garlic is classified into the following three categories.
Garlic in this class must be of superior quality. They must have characteristic of the variety and/or commercial type (this provision does not preclude a
different colouring resulting from smoking).
The bulbs must be:
- regular in shape,
- thoroughly cleaned.
They must be free from defects with the exception of very slight superficial defects which can not, however, affect the general appearance, quality, keeping quality and presentation in the package.
The cloves must be compact.
For the garlic dry, the roots must be cut off flush with the bulb.
Garlic in this class must be of good quality. They must have the tipical characteristics of the variety and/or of the commercial type.
The bulbs must be:
- of fairly regular shape.
The following slight defects are admitted, however, but must not affect the general appearance, the
quality, the keeping quality and presentation in the package:
- small cracks in the outer skin of the bulb.
The cloves must be reasonably compact.
This category includes garlic which can not be classified in the higher classes but that satisfy the minimum requirements specified above.
They may have the following defects, provided the garlic retains the essential characteristics
quality, the keeping quality and presentation:
- Tears in the outer skin of the bulb or the absence of certain parts of the outer skin of the bulb,
- Healed injuries
- Slight bruises,
- Irregular shape;
- Three cloves missing at most.
- Provisions concerning sizing
Size is determined by the maximum diameter of the equatorial section.
- The minimum diameter is fixed at 45 mm for garlic classified in the Extra Class and 30 mm
for garlic classified in categories I and II.
- For garlic presented loose - with cut stems - or in bunches, the difference in diameter between the smallest bulb and the bulb biggest content in the same package shall not exceed:
- 15 mm, when the smallest bulb has a diameter less than 40 mm;
- 20 mm when the smallest bulb has a diameter equal to or greater than 40 mm.
- Provisions concerning tolerances
Tolerances are allowed to quality and size in the same package, or in the case of presented in bulk, in the same a lot of goods, for garlic production not satisfying the requirements of the class.
- Quality tolerances
- Extra Category. 5% by weight of bulbs not satisfying the requirements of the class but in conformity of those of Class I or, exceptionally, with the tolerances of that category.
- Category I. 10% by weight of bulbs not satisfying the requirements of the class but
in conformity of those of Class II or, exceptionally, with the tolerances of that category. Within this tolerance, a maximum of 1% by weight of bulbs may have externally visible sprouts.
- Category II. 10% by weight of bulbs not satisfying the requirements of the class nor the
minimum requirements, with the exception of produce affected by rotting or damaged by frost or
sun, or suffering from any other deterioration rendering it unfit for consumption.
In addition to this tolerance, a maximum of 5% by weight of bulbs may have cloves with germs
- Size tolerances
For all classes: 10% by weight of bulbs not satisfying the requirements size regarding and the size indicated but conforming to the size immediately above and/or below to that identified. Within this tolerance, a maximum of 3% of bulbs may have a smaller size than the minimum diameter requirement, which, however, must not be less than 25 mm.
- Provisions concerning the presentation
The contents of each package, or in each lot in the case that the garlic is presented in bulk, must be uniform and contain only garlic of the same origin, variety or commercial type, quality and size (in the case in which it is obligatory the use of the size criteria). The visible part of the contents of the package, or garlic commercialization lot presented in bulk, must be representative of the whole.
Garlic must be packed in such a manner to ensure adequate protection of the product, with the exception of dry garlic presented in plaits, which can be shipped in bulk (loaded directly onto a means of transport).
The materials used inside the package must be new, clean and of a quality such as avoid causing any external or internal damage to the products. The use of materials, in particular of
paper or stamps bearing trade specifications is allowed provided the printing or labeling has been done with non-toxic ink or glue.
In the case of the bulk presentation, packaging must be free of extraneous bodies.
Garlic should be presented as follows:
1) loose in the package, with cut stems, the stem can not be longer than to:
- 10 cm in the case of fresh and semi-dry garlic
- 3 cm in the dry;
2) in bunches fixed by:
- number of bulbs,
- net weight.
The stems must be evened off;
3) in plaits, only for the dry and semi-products, determined on the basis of:
- the number of bulbs. In this case, each plait must have at least 6 bulbs;
- net weight.
The content for each package, in bunches or plaits, must have uniform characteristics (number of bulbs or net weight).
Whatever type of showing, the stems should be cut net, such as the cut of roots, in the case of dry garlic extra class.
- Provisions concerning marking
Each package must bear the following particulars in letters grouped on the same side, legibly and indelibly marked, and visible from the outside, the instructions below.
For garlic in strings transported in bulk (direct loading into a transport vehicle), these particulars
must appear on a document accompanying the goods, and attached in a visible position inside the
Packer and/or dispatcher: name and address or issued or recognized by an official agency. However, in case of use of a code (symbol), you must indicate next to the code (symbol) the reference packer and/or dispatcher (or equivalent abbreviations).
- Nature of the commercial product
- Garlic «fresh», «semi-dry» or «dry», if the contents are not visible from the outside;
- Name of the variety or commercial type («white garlic», «pink garlic», «red garlic», etc.);
- dove del caso, «smoked».
- Origin of the commercial products: country of origin and optionally, district of garlic growth or national, regional or local area.
- Commercial specifications
- Size (if sized) expressed as minimum and maximum diameters of the bulbs.
- Official control mark (optional).
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Fiume Francesco 2005