Onion

Taxonomy of the Onion (Allium cepa L., 1753) according to Cronquist System

Superkingdom or Domain: Eukaryotae Whittaker et Margulis, 1978
Kingdom: Plantae Haeckel, 1866
Subkingdom: Viridaeplantae Cavalier-Smith, 1998 (Green plants)
Superdivision: Spermatophyta Gustav Hegi, 1906 (Plants with seeds)
Division or Phylum: Tracheophyta Sinnott, 1935 ex Cavalier-Smith, 1998
Sub-Division or Phylum: Magnoliophytina Frohne & U. Jensen ex Reveal, 1996
Class: Liliopsida Brongn., 1843 (Monocotiledoni)
Subclass: Liliidae J.H. Schaffn.,1911
SuperOrder: Lilianae Takht., 1967
Order: Amaryllidales Bromhead, 1840
Family: Alliaceae J. Agardh, 1858
Subfamily: Allioideae Herb., 1837
Tribe: Allieae Dumort., 1827
Subtribus/Sottotribe: Alliinae Parl, 1852
Genus: Allium Linneo, 1753
Species: Allium cepa Linneo 1753

Taxonomy of the Onion (Allium cepa L.) according to APG System
Clade: Eucariotae Whittaker & Margulis,1978
Regnum/Kingdom: Plantae Haeckel, 1866
Clade: Angiospermae
Clade: Monocots
Clade: Unassigned monocots <
Ordo/Order: Amaryllidales Bromhead, 1840
Familia/Family: Alliaceae J. Agardh, 1858
Subfamilia/Sottofamily: Allioideae Herb., 1837
Tribus/Tribe: Allieae Dumort., 1827
Subtribus/Sottotribe: Alliinae Parl, 1852
Genus/Genus: Allium Linneo, 1753
Species/Species: Allium cepa Linneo, 1753



The onion (Allium cepa L.) is a bulbous plant grown from the family of Liliaceae or better, according to the most current taxonomic schemes, Alliaceae. It is a herbaceous biennial that becomes annual by the cultivation. The onion plant have shallow roots and enlarged at the base leaves. The leaves give the edible part. The plant form a long flower stalk carring an umbel inflorescence with flowers yellowish-white. The fruit is a capsule.
Its main use is that of food and seasoning, but it also worked for therapeutic purposes for the properties conferred by science and popular traditions.
It seems that the onion bulbs and other plants of the family have been used as food since ancient times. In the Bronze Age Canaanite settlements, alongside to seeds of figs and dates dating back to 5,000 BC, remains have been found of onions, but it is unclear if they were actually grown at that time.
The literary and archaeological evidence suggest that cultivation may have begun about two thousand years later, in Egypt , along with garlic and leek . It seems that the onions and radishes were part of the diet of the workers who built the pyramids .
The onion propagates , carries and conserves easily. The ancient Egyptians have made ​​the onion an object of worship , because they believed that its spherical shape and the concentric rings were a symbol of eternal life. The use of onions in the burials is shown by the remains found in the eye socket of Ramesses II.
The Egyptians believed that the strong aroma of onions could give back the breath of the dead . In ancient Greece, athletes ate large quantities of onion because it was believed that they alleggerissero blood. Roman gladiators rubbed his body with onion to firm up their muscles.
During the Middle Ages, the onions were of great importance as food, so they were used to pay the rent and as gifts . The Physicians prescribed the onions to relieve headaches and to treat snakebite and hair loss.
The onion was introduced to America by Christopher Columbus on his trip to Haiti during 1493 . In the sixteenth century the onions were also prescribed as a cure for infertility , not only in women but also in pets.
Onions are rich in vitamins and minerals. The characteristic smell of the bulbs is due to the abundance of sulfoxides.
Slice the onions produces tears from the eyes because the aromatic compounds of the onion bulb combine with the allinase, an enzyme that is released abundantly due to the cut. The combination of these elements produces sulfenic acids and sin-propanethial-S-oxide, a volatile gas , which , when it comes into contact with the aqueous humor on the eyeball, it is transformed into sulfuric acid . The contact with the sulfuric acid causes an reaction immediate of eye defense, consisting in the production of tears, but the increased amount of tears of the eye, it transform a greater amount of propylene oxide in sulfuric acid , in a chain reaction. It is, however, an sulfuric acid of consistency very bland, therefore not harmful to the body. To reduce the amount of gas released, one of the solutions adopted during the cut of the onions without tears, it is to do it under running water.
The onion, also known as the bulb onion or common onion, is used as a vegetable and is the most widely cultivated species of the genus Allium. This genus also contains several other species variously referred to as onions and cultivated for food, such as the Japanese bunching onion (Allium fistulosum), the Egyptian onion (Allium Îproliferum), and the Canada onion (Allium canadense).
The name "wild onion" is applied to a number of Allium species but Allium cepa is exclusively known from cultivation and its ancestral wild original form is not known, although escapes from cultivation have become established in some regions. The onion is most frequently a biennial or a perennial plant, but is usually treated as an annual and harvested in its first growing season.
The onion plant has a fan of hollow, bluish-green leaves and the bulb at the base of the plant begins to swell when a certain day-length is reached. In the autumn the foliage dies down and the outer layers of the bulb become dry and brittle. The crop is harvested and dried and the onions are ready for use or storage. The crop is prone to attack by a number of pests and diseases, particularly the onion fly, the onion eelworm and various fungi that cause rotting. Some varieties of Allium cepa such as shallots and potato onions produce multiple bulbs.
Onions are cultivated and used around the world. As a foodstuff they are usually served cooked, as a vegetable or part of a prepared savoury dish, but can also be eaten raw or used to make pickles or chutneys. They are pungent when chopped and contain certain chemical substances which irritate the eyes. Onions contain phenolics and flavonoids that have potential anti-inflammatory, anti-cholesterol, anticancer and antioxidant properties.
A number of synonyms have appeared in its taxonomic history: Allium cepa is known exclusively from cultivation, but related wild species occur in Central Asia. The most closely related species include Allium vavilovii (Popov & Vved.) and Allium asarense (R.M. Fritsch & Matin) from Iran. However, Zohary and Hopf state that "there are doubts whether the Allium vavilovii collections tested represent genuine wild material or only feral derivatives of the crop."
The vast majority of cultivars of Allium cepa belong to the "common onion group" (Allium cepa var. cepa) and are usually referred to simply as "onions". The Aggregatum Group of cultivars (Allium cepa var. aggregatum) includes both shallots and potato onions.
The genus Allium also contains a number of other species variously referred to as onions and cultivated for food, such as the Japanese bunching onion (A. fistulosum), Egyptian onion (A. Îproliferum), and Canada onion (Allium canadense).

Diffusion area of the onion
Onion is grown in Italy on about 16,000 ha with a production of about 500,000 t, which places the Italy, along with the Netherlands, after the Spain as the first European manufacturer with around 1 million tonnes. The business's competition of these Countries and the lack of uniformity of the italian product have greatly reduced our exports that now stand at around 40,000 t particularly towards the Germany and France.
Italian imports regard about 25,000 tonnes coming from France for more than half. The productions in our country are predominantly located in Emilia Romagna ( 28% of national production) , in Piedmont (13% ), Sicily (11%) , Veneto (10%) , Puglia ( 9%) and Campania ( 8%). In Umbria is estimated to have grown a few tens of hectares.
In the United States the onion is diffused in central and southern areas.

Botanical characteristics The onion plant (Allium cepa) is unknown in the wild but has been grown and selectively bred in cultivation for at least 7,000 years. It is a biennial plant but is usually grown as an annual, with a biennial seed production, annual bulb production, the latter being the edible part.
The onion is generally very rich in water (more than 90%) even if the dry substance in cultivars intended for the dehydration can exceed 20%. The bulb is almost devoid of starch but accumulates soluble carbohydrates (mainly glucose, sucrose, fructose) in high quantities (5-6 g per 100 g of edible part). In general, the onion has a low energy value (26 cal/100 g of edible part ) and a high content of potassium (140 mg/100 g). The characteristic flavourr, aroma and tear the action conferred by some volatile sulfur compounds that are formed from some precursor odorless and non-volatile when the plant tissues are damaged bulb. This explains why the whole onions boiled see greatly reduced the emission of characteristic odor and flavor. The sulfur compounds in onions and/or some derivative compounds have medicinal properties capable of preventing atherosclerosis, inhibit platelet aggregation, lower blood pressure and cholesterol, promote diuresis and, finally, have antibacterial and antifungal properties.

Vegetative cycle and phenological stages
The stages of germination and emergence have a variable duration from 8 to 20 days after sowing, in depending on weather conditions and the time of sowing.
The cotyledon, after germination, appears as a loop or hook above the surface of the soil. In relation to the sensitivity of the cotyledon and its poor penetration ability, it is evident how the emergency phase is very critical, therefore, the soil must not have absolutely the surface crust.
The seedling growing carried out from the soil surface the cotyledons that often trail with oneself also the seed integuments that are blacks. The cotyledon assumes a typical horizontal position respect to the soil which is named "flag stage". In the middle of the seedling stem born and then grows the first true leaf. After the appearance of the second and third true leaf, the cotyledons progressively empties of the reserve substances and finally dries
Meanwhile, the seminal root elongates rapidly but with the formation of the first true leaves degenerates and it is replaced by a system composed of fasciculated adventitious roots, unbranched, numerous but short enough.
With the arrival of the fourth true leaf, the collar of the plant starts to thicken, while the first leaf begins to wilt. During the formation of the fifth, sixth and seventh leaf, it is possible to observe the completely drie and the fall of the first leaf and the start of the senescence of the second leaf.
Essentially in function of the photoperiod (day length > 12 hours), the plant begins the "bulbification", that is it starts sending reserve substances to the basal part of the leaf sheaths and form the bulb. During this phase, the second and third leaf dry up, while form leaves from the eighth to the thirteenth and the plant reaches its maximum height (generally the longest leaf is the seventh or the eighth, and the subsequent ones gradually shorter).
During the bulbification the internal youngest leaves (> of the 13th) is not longer able to bring out the leaf lamina towards the outside and remain in the form of fleshy scales within the bulb, contributing to its enlargement. The beginning of the bulbification can be externally identified, in grossly way, when the ratio between the maximum diameter of the bulb and the minimum diameter of the collar is equal to or greater than 2.
The phase of enlargement of the bulb is actively pursuing for about 6-8 weeks at the same time the gradual desiccation of 4-6 st leaf and the tips of the youngest leaves. The leaves then begin to bend under its own weight. During this phase can appear 1-2 new short leaf laminas and the protective outer bulb tunics begin to form.
The collar begins to empty as the new leaf laminas cease to grow inside, its tissues lose their turgidity and soften determining the sway of the leaf under its own weight.
In the final phase of the cycle has the maturation of the bulb with the desiccation of the protective outer tunics and the complete leaf senescence.
It been shown that the bulb during this stage, despite not having more photosynthetic activity, can further increase of weight due to translocation of the substances accumulated in the leaves.
The bulb has at the harvesting, a dormancy period more or less prolonged as a function of cultivars and this affects the ability of conservation and the predisposition to mount in flower more or less quickly: in cultivar spring harvest the resting phase is short or absent, the possibility of poor preservation and the climb is easy and quick to flower; cultivars harvested in late summer-autumn, however, the resting phase is long, the storage can be prolonged, the climb to flower occurs after vegetative growth if are fulfilled the needs of vernalization.

Needs pedo-climatic

Photoperiodic and thermal requirements
The thermal requirements of the main vegetative stages are shown in table 1. Although the minimum temperature for germination is slightly above zero, at low temperatures this phase is very slow (at 5oC takes about a month); the temperature optimum is found in a wide range with the average time of germination that, in any way, are rarely less than a week. It 'during the emergency phase that the onion is particularly sensitive to frost although you can find a high variability among cultivars.

Table 1 - Thermal requirements of the onion.
Stage and type of temperature ░C
Seed germination
minimum
optimal
Leaf growth
minimum lethal
basis
optimal
maxim

1-2
13-28

-8/-11
6
20-27
30


The issuance of the leaves is highly dependent on the temperature: growth rates are linearly increasing between 6 and 20 ░ C, consistently elevated between 20 and 27 ░C and decreasing linearly between 27 and 30 ░C.
The process of bulbificazione is essentially regulated by photoperiod. The onion, in fact, in general it is a species long day, that is, the bulbification only happens if the day length exceeds a certain threshold that varies according to the cultivar and that affects the area and the time of planting (Table 2 ).

Table 2 - Photoperiodic requirements for the bulb formation.
Time of the sowing or transplant h of light
Summer-autumn
Late winter-early spring
Piena primavera
12
14
16


The varieties of onion that have a threshold of 12 hours of light to produce the bulbs are named to "short day" (early cultivars), those that have a threshold of 16 hours are, however, commonly referred to as onions to "long day" (tardive CultiVars). As long as the plant does not see fulfilled the photoperiodic needs of bulbification constantly producing leaves and does not form the bulb is the case of a long day cultivars planted in the fall or early spring. Conversely, if the bulbification starts too early few leaves which form the plant will not be able to ensure photosynthetic activity sufficient to sustain the optimum enlargement of the bulb and the achievement of high production: the case of short-day cultivars implanted spring.
The process of bulbification is, however, also influenced by temperature: the temperature increases (between 10 and 25 ░C) the process of bulbification proceeds faster and the critical threshold of day length tends to decrease. In general, more the plant is large at the time of the bulbification induction, more the reaction is rapid.
Finally it should be pointed out that the process of bulbification is a reversible process: if the plant, after having begun the enlargement of the bulb, is to perform the final part of the cycle under short day and low temperature stops and starts again swell the bulb to produce leaves. This phenomenon is, for example, quite frequent in northern Europe where there is spring-like implant and tardive cultivars.
The flowering induction and the the formation of the floral scape is determined by the temperature and is favored by temperatures between 5 and 15 ░C. The short-day cultivars autumn planted can bloom in the following spring if the bulbs are not harvested and the plants are left in the field. The long day cultivars (those tardive) sown in spring must elapse, however, the winter to see fulfilled the needs of vernalization to flower induction. These issues give us useful information to avoid the phenomena of pre-flowering that are detrimental to the regular growth of the bulbs for the production of which is cultivated onion. In general, the sensitivity to pre-flowering varies with the cultivar, increasing with early implants of onion (more common with autumn implants) and with seasonal trends first mild, favoring the growth of the plant, and then cold.

Needs of water
It's especially important for onions to get water just after planting. A well-hardened transplant can survive almost two weeks in dry soil. But, in the long run, early dryness will hurt the crop. The bulbs just won't measure up at the end of the season.
Watering perils: if soil is allowed to dry out during bulb formation, the onion may split and form two bulbs. It helps to apply mulch when the tops are 25-30 cm (10 to 12 inches) tall, because the mulch helps retain moisture.
Because their roots are so shallow, onions dry out faster than many other crops during a drought. When that happens, the onions often mature early, and that doesn't help the size of the bulbs. Must remember the Watchword "Don't let onions dry out".
Many people in the West and Southwest must irrigate their home gardens all season long, while gardeners in other parts of the country may face a dry spell of several weeks during the season. Where water is in good supply, people turn to sprinklers and furrow irrigation to keep gardens supplied with water. In areas where water isn't plentiful, moisture-saving drip or trickle irrigation can be a life-saver.
When to Water: if you use a hose or sprinkler to water your garden, remember it's best to water early in the morning rather than during the heat of the day. Too much water is lost to evaporation if you water when the sun is high.
Watering onions and other plants from above in the evening can leave plants with wet foliage overnight. Often that can be an invitation to trouble, because with moisture remaining on the leaves, disease can spread rapidly.
Onions do need a lot of water, but the soil should not be soggy all the time. "Just enough" water is better than "too much." Ideally, you want to provide a thorough soaking to a depth of six inches once a week rather than just a light sprinkling each day.
Watering Guidelines: here are some guidelines for watering. Needs of Soil
Onions will grow in practically any kind of soil but, one that's rich in decayed organic matter and humus and drains well is best. Heavy soils that stick together after rain will bake hard when the sun comes out, making it difficult for the bulbs to expand. Another problem with heavy soils is that water stays on the surface in puddles. That can drown plants! Southern gardeners can overcame this problem by making raised planting beds that are about 25 cm (10 inches) wide and 10-12 cm (four to six inches) high. When it's time to plant onion sets in January, your raised seedbeds won't be too wet to plant. The planting beds drain well and leave the soil moist but not packed, soggy or impossible to work.
The sandy soils can be planted with a suitable pH condition and a regular water supply. The depth of the soil, however, is almost never a limiting factor taking into account the reduced root development. The stagnant water, finally prepare the bulb to rot and other parasitic adversity. The onion is sensitive to salinity: up to an electric conductivity of saturation of the soil (ECe) of 1.2 mS/cm is not ahave the adverse effects, with ECe = 1.8 mS/cm, there is a decrease of production of 10%; with ECe = 2.8 mS/cm is estimated a decrease in production of 25%; with ECe = 4.3 mS/cm they yeld decrease of 50%; with ECe = 7.4 mS/cm, the production is totally compromised.

Varieties
There are many varieties of onions, which take typically the name of the cultivation areas, the shape, the color, the size of the bulb, the earliness or, more generally, from the color of the outer skin (tunic). This tunic can be white, golden-yellow or red.
Depending on the color of the bulb, the onions can be distinguished os following:
In addition to the variety traditionally grown and cheaper, there are nowadays hybrid variety, capable of provide greater uniformity of size, more productive potentials, but higher cost.
The following is a breakdown of the main varieties and hybrids currently grown.

- Varieties to short day for autumn sowing:
Variety with white tunic:
May White selection Karina
Variety: standard.
Tunics: bright white color.
Bulb shape: globular large.
Maturation: mid-May.

Blanca De Fuentes
Variety: standard.
Tunics: bright white.
Bulb shape: round.
Maturation: mid-May.

- Varieties with golden tunic:
Senshyu Yellow
Variety: standard.
Tunics: golden yellow color.
Bulb shape: globular.
Maturation: early June.

Earl Yellow Globe KW
Variety: standard.
Tunics: yellow.
Bulb shape: round.
Maturation: late May.

Olimpic
Variety: Hybrid.
Tunics: yellow.
Bulb shape: spherical.
Maturation: early June.

Top Star
Variety: standard.
Tunics: yellow.
Bulb shape: round.
Maturation: late May.

- Varieties with red tunic:
Electric
Variety: Hybrid.
Tunics: dark red.
Bulb shape: round.
Maturation: early June.

- Long-day Varieties with sown in late winter:
Varieties with white tunic
Blanco Duro
Variety: standard.
Tunics: white.
Bulb shape: round-globular, slightly elongated, large in scale.
Maturation: late July-early August.

Comet
Variety: Hybrid.
Tunics: bright white color.
Bulb shape: globular with medium-large sizes.
Maturation: early-mid August.

Primo Blanco
Variety: standard.
Tunics: bright white.
Bulb shape: round uniform size medium-high.
Maturation: early August.

Sterling
Variety: Hybrid.
Tunics: white.
Bulb shape: round uniform.
Maturation: late July.

Silverstone
Variety: Hybrid.
Tunics: white.
Bulb shape: round.
Maturation: early August.

Varieties in golden robe
Densidor
Variety: standard.
Tunics: bronzed brilliant.
Bulb shape: round.
Maturation: early August.

Vaquero
Variety: Hybrid.
Tunics: yellow bronze.
Bulb shape: round-spherical.
Maturation: late July.
Notes: address by industry

Density
Variety: standard.
Tunics: yellow bronze.
Bulb shape: round.
Maturation: early August.

Golden of Parma
Variety: standard.
Tunics: golden yellow.
Bulb shape: globular.
Maturation: late July-early August.
Notes: easy rupture of the tunic.

Croket
Variety: Hybrid.
Tunics: dark golden and shiny.
Bulb shape: round.
Maturation: middle August.

Gunnison
Variety: Hybrid.
Tunics: golden.
Bulb shape: round.
Maturation: early August.

Varieties with red tunic
Rossa d'inverno selection Rojo Duro
Variety: standard.
Tunics: blood red.
Bulb shape: globular spinning top of medium-high sizes.
Maturation: August.

Sanguigna di Milano selection Reddy
Variety: standard.
Tunics: strong red.
Shape of the bulb: high spinning top, medium-high sizes.
Maturation: August.

Redwing
Variety: Hybrid.
Tunics: red.
Shape of the bulb: Maturation: middle August.
Bulb shapee: elongate round.
Maturazione: inizio agosto.

Other Italian varieties of great local importance and special characteristics of quality, are:: It is cultivated between Nicotera, in the province of Vibo Valentia, and Campora San Giovanni, in the town of Amantea, in the Cosenza province, along the Tyrrhenian coast. It is mainly produced between Briatico and Capo Vaticano in the municipality of Ricadi. The particular substances contained in the soil of this area make it sweet and not bitter. It is cultivated in these areas for more than two thousand years, imported by the Phoenicians, and for over a century, now combined with tourism, contributes to the socio-economic development of the area. The sweetness of the vegetable depends on the microclimate stable in winter, without changes in temperature for the action of meekness exercised by the proximity of the sea, and fresh and loamy soils, which determine the characteristics of high-quality product.
This vegetable contains vitamin C, vitamin E, iron, selenium, iodine, zinc and magnesium. The shape is round or ovoid.
The bulb has many beneficial effects; one of these is the power antisclerotic that brings benefit to the heart and arteries, and prevents the risk of heart attack.
It is composed of several concentric tunics fleshy, white-colored and red wrapper. One of his property is to be a natural sedative, useful to facilitate sleep.
Recently it is found that contains nitrogen oxide, molecule involved, inter alia, in the mechanism of erection. Pliny the Elder in his Naturalis Historia , refers to red onion as a remedy to cure a variety of ills and physical ailments.
The taste is determined in particular by the consistent presence of sugars such as glucose, fructose, sucrose. It is easily digestible. Contributes to dietary intake by about 20 calories per 100 grams of fresh product.

Figure 1 - Bulbs of "cipolla di Tropea" forming part of some compositions, of which the last is to braid.

the name of Acquaviva delle Fonti, a charming resort in the province of Bari, is tied to the wide availability of fresh water, which flows for a clear perennial underground aquifer. In addition to this element, then there is the quality of the soils. Well-drained soils and good airy, deep, rich in potassium, with an good mix of solid parts, which tends to muddy. These features are ideal for the cultivation of onion, so that the bulbs grown in these soils, since from 800, was also valued and traded on markets outside the region. Renowned for its sweetness, the "cipolla rossa di Acquaviva delle fonti" is also recognizable for the typical flattened shape: a large disc with a thickness of 2-3 cm (0.79-1.18 inchs) wide, up to a foot, and weighing about 500 g (17.64 oz). Its color is between purple-red and violaceous, clears towards the inside, up to become completely white. The cultivation happens in accordance to the ancient tradition and in a natural way. This variety sown in September, to the waning moon, and harvested from early July until August. The cultivation of Acquaviva onion is limited to the territory of the Municipality. The reason is, in part, in the inherent characteristics of the variety, in part, in the type of cultivation that remains largely manual. By keeping intervention to a minimum of a chemical, it is necessary an extra dose of work in the field: the weeding and hand weedings (manual operations of weeding the field rows) must be frequent and this is also reflected on the cost of the final product.
On 30 and 31 August in Acquaviva delle Fonti (Bari) it is held the Festival of the red onion and of the "calzone" a unique opportunity to taste the "calzone", a rustic prepared with onion, hot ricotta and olives pitted. The cheese used, acidified and matured for three months in terracotta containers, has a pungent odor and strong flavor and spicy, which blends well with the freshness and sweetness of the bulb of Acquaviva. But you can not leave Acquaviva delle Fonti without having tasted the lamb baked with onions, focaccia with olives, onions, anchovies and capers, onions cooked in the oven in a baking dish, in the traditional clay pot or, much more Put simply, a salad of red onions raw, sweet, seasoned with extra virgin olive oil and a little salt. Match obligation, a good local Primitivo wine.

Figure 2 - Typical bulbs of the "Cipolla rossa di Acquaviva delle fonti".

it is a typical product grown exclusively within the area of ​​Castelleone Suasa (Ancona) and San Lorenzo in Campo (Pesaro-Urbino). The onion has the bulb tunics of color rosaceous and has a sweet taste.
In 1999 the municipalities of Castelleone di Suasa and San Lorenzo in Campo with the assistance of the Province of Ancona and the agency ASSAM have started a program of re-discovery, use and disclosure of this typical product cultivated at least since the beginning of the twentieth century. The Research Units for Horticulture Monsampolo del Tronto CRA provided for the selection of seed genetics to identify the original ecotype and to improve the quality of the bulb.
The tourism association ProSuasa brought to the knowledge of the public and of all people about this product rediscovered organizing the annual "Onion Festival". Around this ingredient have developed different recipes and products: from the most traditional fried onions in sweet sour sauce, to gratin as the most unusual ice cream onion, onion jam and the "Cipollino", a onion liqueur.

Figure 3 - Bulbs of "Cipolla di Suasa" and a typical composition of the local braid.

the cultivation of these onion was born and perpetuated in the area of Montoro Inferiore town in the countryside and surrounded by hills. The cultivation of this particular product has is extended over the years, even in other areas of the province of Avellino, especially in the vicinity of Montoro Superiore and Solofra. In this area, has found soil and climatic conditions suited to its organoleptic characteristics. It prefers mostly well-drained soil rich in organic matter. Among the various specialties, the "cipolla ramata di Montoro", often grown in combination with the corn is harvested in the second half of June and is one of the most important productions of the vegetable in the province. Unlike the other onions from Serbia, it has an elevated resistance to cooking, a feature that adds to the already considerable organoleptic qualities that make it a very popular on the domestic and international markets. It has a sweet taste and smell intensely aromatic, excellent for any food preparation.

Figure 4 - Bulbs of the "Cipolla ramata di Montoro".

pale yellow bulb-shaped flattened, small size and thin skin. Ivory-white flesh is firm, flavorful. Medium-early, in an average day. Of discrete shelf life, is used for both the fresh market and for canning. The sowing takes place from February to April in the open field broadcaster. The harvest lasts from July to August. The onion borrettana, besides the traditional processing, is also subjected to a further working process: peeling. It produces small, flattened, yellowish, easily preserved fruits.

Figure 5 - Bulbs of the "Cipolla borrettana" variety.

Figure 6 - "Cipolle borrettane" naturally harvested and immediately processed, retain intact aroma and flavor. They are of equal size and can also be used as such.

small, white, excellent for the preparation of pickles in Brumate in the area of ​​Lake of Como.

Figure 7 - A pickled od onions of Brunate.

in Cannara, a small town in the heart of the southern of the Umbria Valley, less than 10 km from Assisi and lies on the left bank of the river Topino, the onion is grown since centuries. The soil are clayey-sandy, rich in silica, and sufficiently porous with good drainage capacity. They provide the ideal characteristics for the development of the bulb that needs frequent watering but does not tolerate water stagnation. In Cannara it can find three ecotypes of onion: 1) the Red, having a bulb deep red spherical and flattened at the top, 2) the yellow bulb flattened straw yellow in color, 3) and Golden, with a golden bulb similar to a spinning top and with the top flattened.
The red is the most popular due to its sweetness and digestibility, that make it great even raw.
In Cannara the cultivation of onions, still completely manual, it's tied to the traditions and culture of the peasant, in fact every year the first week of September it is held the Feast of the "Cipolla di Cannara", where you can witness the tying of onions in features braids and clusters, according to long-established customs of the local population.
The "cipolla di Cannara", in addition to being an italian traditional food product in the Umbria region, it is also part of the "Ark of the Taste" of the "Slow Food Foundation".

Figure 8 - An ecotype of the "cipolla di Cannara".


Sweet onion varieties
A sweet onion is a variety of onion that is not pungent. Their mildness is attributable to their low sulfur content and high water content when compared to other onion varieties.
Origins in the United States: United States sweet onions originated in several places during the early twentieth century.
"Vidalia onions" (Figure 9) were first grown near Vidalia, Georgia in the early 1930s. Today the name refers to onions grown in a 20-county production region in the state of Georgia as defined by both Georgia state and federal law (CFR).
"Vidalia Onions" are available in your local grocery store or farmers's market from late spring through the summer. Look for firm, plump, shiny skin with a yellowish tint and no discoloration at the stem. Look for onions with a mild, light aroma; a strong odor indicates decay. To store Vidalia Onions, keep them individually wrapped in paper towels in a cool, dry place
A medium-sized "Vidalia Onion" has only 60 calories, and is a good source of Vitamin C and fiber. The onions also contain the phytochemical allicin, which may aid the body in fighting infection, as well as help lower cholesterol and blood pressure.
The "Walla Walla sweet onion" is named for Walla Walla county in Washington where it is grown. Its development began around 1900 when Peter Pieri, a French soldier who settled in the area, brought a sweet onion seed from the island of Corsica with him to the Walla Walla Valley. This sweet onion was developed by selecting and reseeding onions from each year's crop that possessed sweetness, jumbo size, and round shape.

Figure 9 - Bulbs of "Vidalia onions". Vidalia Onions were named after the farmers's market in Vidalia, Georgia where the sweet — not pungent — onions were first introduced to the public. Due to their enormous popularity, these sweet, juicy onions were named the official state vegetable of Georgia in 1990.


Other U.S. varieties are raggroupped such as of following:
Pungency in onions. The pungency in onions measures pungency with units of Ámol/gfw (micromoles per gram fresh weight). It is named after pyruvic acid, the alpha-keto acid co-product created in the biochemical pathway that forms syn-propanethial-S-oxide, the main lachrymatory agent in onions.
The standard onion has an eight rating, while "sweet onions" have a two or three rating on the scale. The lower the score or scale the more "sweet" the onions are rated. Anything less than five is considered a sweet onion.
Most varieties are considered sweet and must have a score of 5.0 Ámol/gfw or less. The "Supasweet onion" (usually grown in Lincolnshire, England) registers 1.5 to 2 on the scale. A standard brown onion is usually in the range of 6-7 out of 10.
Soil type, rain, and sunlight affect the pungency in onions and garlic and, therefore, their score on the pyruvate scale.

Cultivation
The onions are grown for their green stems and their bulbs. They need a soil rich and moist but not too soggy water. Different types of onions require different climatic conditions and several hours of sun each day. Growing from seed is done by planting the seeds directly into the soil to a depth of 1 cm, leaving about 10 cm of space from plant to plant. Once it has been sowing must wait 90 to 120 days before harvest. In mite climates the onion can be grown even in the winter, but the onion plant is typically spring.
Onions are best cultivated in fertile soils that are well-drained. Sandy loams are good as they are low in sulphur, while clayey soils usually have a high sulphur content and produce pungent bulbs. Onions require a high level of nutrients in the soil. Phosphorus is often present in sufficient quantities, but may be applied before planting because of its low level of availability in cold soils. Nitrogen and potash can be applied at intervals during the growing season, the last application of nitrogen being at least four weeks before harvesting. Bulbing onions are day-length sensitive; their bulbs begin growing only after the number of daylight hours has surpassed some minimal quantity. Most traditional European onions are what is referred to as "long-day" onions, producing bulbs only after 14 hours of daylight occurs. Southern European and North African varieties are often known as "intermediate day" types, requiring only 12–13 hours of daylight to stimulate bulb formation. Finally, "short-day" onions, which have been developed in more recent times, are planted in mild-winter areas in the fall and form bulbs in the early spring, and require only 11–12 hours of daylight to stimulate bulb formation. Onions are a cool-weather crop and can be grown in USDA zones 3 to 9. Hot temperatures or other stressful conditions cause them to "bolt", meaning that a flower stem begins to grow.
Onions may be grown from seed or from sets. Onion seeds are short lived and fresh seed germinates better. The seeds are sewn thinly in shallow drills, thinning the plants in stages. In suitable climates, certain cultivars can be sown in late summer and autumn to overwinter in the ground and produce early crops the following year. Onion sets are produced by sowing seed thickly in early summer in poor soil and the small bulbs produced are harvested in the autumn. These bulbs are planted the following spring and grow into mature bulbs later in the year. Certain cultivars are used for this purpose and these may not have such good storage characteristics as those grown directly from seed.
Routine care during the growing season involves keeping the rows free of competing weeds, especially when the plants are young. The plants are shallow rooted and do not need a great deal of water when established. Bulbing usually takes place after twelve to eighteen weeks. The bulbs can be gathered when needed to eat fresh but if required to be kept in store, should be harvested after the leaves have died back naturally. In dry weather they can be left on the surface of the soil for a few days to dry out properly, then they can be placed in nets, roped into strings or laid in layers in shallow boxes. They should be stored in a well-ventilated, cool place such as a shed.

Crop rotation and Succession Cropping

Crop rotation. Historic crop rotation methods are mentioned in Roman literature, and referred to by several civilizations in Asia and on three major elements: sophisticated systems of crop rotation, highly developed irrigation techniques and the introduction of a large variety of crops which were studied and catalogued according to the season, type of land and amount of water they require. In Europe, since the times of Charlemagne, there was a transition from a two-field crop rotation to a three-field crop rotation. Under a two-field rotation, half the land was planted in a year while the other half lay fallow. Then, in the next year, the two fields were reversed. Under three-field rotation, the land was divided into three parts. One section was planted in the Autumn with winter wheat or rye. The next Spring, the second field was planted with other crops such as peas, lentils, or beans and the third field was left fallow. The three fields were rotated in this manner so that every three years, a field would rest and be unplanted. Under the two field system, if one has a total of 600 fertile acres of land, one would only plant 300 acres. Under the new three-field rotation system, one would plant (and thereby harvest) 400 acres. But, the additional crops had a more significant effect than mere productivity. Since the Spring crops were mostly legumes, they increased the overall nutrition of the people of Northern Europe.
Two-field rotation was practised by the ancient Greeks.
Tree-field rotation was already mentioned in the Roman literature, and referred to by great civilizations in Africa and Asia. From the end of the Middle Ages until the 20th century, the three-year rotation was practised by farmers in Europe with a rotation: rye or winter wheat, followed by spring oats or barley, then letting the soil rest (fallow) during the third stage.
A four-field rotation was pioneered by the Dutch in the late medieval ages.


Figure 10 - Top. Landscape where crop rotation is not taken very seriously. Below. Landscape where crop rotation is taken very seriously



To follow a simple four-year crop rotation, divide your garden into four areas or plots. Plot One, Plot Two, Plot Three, and Plot Four. In each of the next four years, grow a different crop or different members of the four crop families in a different plot following this rotation: This four-year crop rotation intersperses members of the other vegetable crops among members of the onion. Here is how they are grouped: garlic, leeks,lettuces, shallots, sweet corn, squashes, zucchini, and pumpkins (marrow and courgettes), perennial Vegetables.
The onion crop is considered a renewal, which opens the rotation. Being very susceptible to the phenomenon of soil fatigue is essential to implement a rotation at least every three years, then follow up with cereal crops, grassland, carrot, radish and salad. If there are having problems with fungal diseases (Fusarium in particular) or nematodes, it would be appropriate not to bring back the onion on the same ground before 7-8 years. To avoid reductions in production and deterioration of quality it should avoid it followed a cabbage, potato or sugar beet as characterized by phytosanitary problems similar to those of the onion (Figure 10).

Succession Cropping. Succession cropping will help you get the most out of your vegetable garden. Here are two succession cropping strategies: When planning your succession cropping keep the following in mind: For onions, in our italian regions, the recommended succession crops is Spring harvest cabbage.

Succession Planting Summer into Autumn. Succession plantings for autumn harvest are made in early- and mid-summer.
Succession planting is the practice of planting a new crop in the same spot where another crop has just been harvested.
Crops for succession planting in early- and mid-summer are cool-season crops—crops that mature and yield best when temperatures average in the 10 ░C and 15 ░C, not the 21 ░C and 27 ░C, temperatures preferred by warm-season crops.
Crops to plant for fall harvest include: snap beans, lima beans, cabbage, carrots, Chinese cabbage, beets, broccoli, cauliflower, kale, lettuce, bunching onions, radish, spinach, winter squash, and turnips. Warm-season crops can be succession plantings but the weather must stay warm enough into autumn for them to ripen.
Successful succession cropping requires timing: make sure there is enough time for the succession crop to germinate and grow to maturity before cold weather arrives. (Check the seed packet to learn how long a crop will take to germinate and reach maturity, then make sure there are enough days left in the season before the date of the average first frost in your area.) A frost and freeze will knock down and even kill some cool-season crops, but some cool-season crops can survive a frost or freeze if they are close to maturity and harvest.
When choosing succession crops, be sure that they get enough sunlight and are not shaded out by neighboring warm-season crops nearing maturity.
Onions interesting, here is a list of warm-season crops and suitable cool-season crops to follow in succession planting:
Soil Preparation
Proper soil preparation is a very important task for the onion, as it should to avoid conditions that favor stagnant water resulting in the development of rotten in the bulbs. This phenomenon is particularly severe in clay soils, in which a poor draining of the water favors the attack by Fusarium spp. Is typically accomplished by plowing to 30-40 cm depth, with eventual burial of crop residues. The plowing can be even more shallow if combined with plowing at 50-60 cm, for this purpose the plow subsoiler guarantees a good preparation of the soil with a saving of time and fuel. The burial of manure should only occur if it is ripe, to avoid encouraging the development of fungal diseases. It is then carried out of the ground with the amminutamento milling or harrowing in early August for the crop cycle summer-autumn or late winter crop cycle in spring-summer. A sunny, well-drained site is essential for growing good crops of onion and garlic. It's possible to grow good onions on heavy soil, but the drainage should be improved prior to planting with grit and bulky organic matter, and the cloves planted in ridges of soil 10 cm high to help reduce soil moisture.
Onions and garlic both like fertile soil, but neither require much nitrogen and so shouldn't be grown on freshly manured soil. Instead, dig over and manure the ground several months before planting. If the soil is acid it's worth liming it so its pH level becomes neutral or even slightly alkaline.
For small surfaces is sufficient manual digging or hoeing with burial of ripe manure or compost at the rate of 20-30 kg per 10 m2. Also in this case it is appropriate not to exceed with the addition of organic matter, pointing out that the onion benefits of organic inputs made ​​to the previous crop.

Planting
The time of planting depends on the intended use of the product. For the onions for fresh consumption seeding runs from mid-August to mid-September or February, the transplant is instead performed from September to December. The onions are sown from Serbs from January to April with harvesting summer-autumn, while the onions are sown directly in the field from February to April. For home gardens, in which the production are the most common bulbs swell, the plant occurs from late winter to early spring.
The details of the planting of the onion can be distinguished: Generally on large surfaces is preferred direct seeding, while for small extensions and gardens it prefer to transplant or plant bulbs. The planting is a must for the onions to industry due to the high plant density.

Sowing
The sowing of onion can be performed with mechanical seed drills or pneumatic seed drills. This last allow a more uniform distribution along the row. The working width is 140 cm; the plants are at 30 cm on the rows.
Modern sowing of the onion is done with precision air seeders, using seed bare or wrapped with a coating (pelleted seed) that ensures better uniformity and precision sowing. A further alternative is the use of seed place on tapes of biodegradable material, which decomposes in contact with the soil. This system allows a saving of seed and a reduction of the subsequent thinning operations.
To evaluate the distance of planting is appropriate to consider the final destination of the product. For large bulb onions, the rows should be at 15-20 cm, while for the small bulb onions is 10 cm. This distance may dicrease to 5-10 cm for pickles onions, for which the seed can be also carried broadcaster . The distance between the seeds in the row varies from 2-3 cm for the onions to 15 cm for the onions with larger bulb . The quantity of seed used will therefore vary from 5-6 kg per bulb cultivars bigger up to 60-100 kg for onions. The seed should be placed at a depth of 2-3 cm , performing a rolling to allow the soil to adhere adequately to the seed.
The seedlings for transplantation are produced in the plant nursery. The seed is sown from seeder automatic which aspire one seed from the hopper and drop it in the container cell at the same depth). The containers are alveolars in polystyrene containing the growth substrate. The plantlets are ready for transplanting in open field 40-80 days (depending on ambient conditions) from the sow to get 3-5 leaves (Figure 11).

Figure 11 - Production of onion seedlings in plant nursery for transplant in open field. This technique of seedling obtaining in the nursery and subsequent transplant in open field has the advantage to shorten the growing cycle from sow to bulb harvesting, to avoid the thinning in the field, to uniform the growth of the young plants.

Transplant
The transplant is performed by hand or by machine for small areas (Figure 12). The seedlings are planted 4-5 cm dept, with possible trimming of the roots.

Figure 12 - This specific semi-automatic transplanter for transplanting of vegetable crops seedlings, both bare-root and rooted in peat lump, conic-pyramidal or cubic, it is particularly suitable for onions transplant. Foxdrive R14 ensures an uniform transplant depth, a constant distance between the rows and on the row, a perfectly perpendicular planting and an optimal ridging. The machine estimated yield is 2000 plants/hour per row.


Before transplanting the seedlings can be immerse for 12 hours in a solution containing 20 ppm of indoleacetic acid or naphthalenacetic, in order to cause the early enlargement of the bulb. The operations of watering, fertilizing and pesticide treatments are carried out automatically and programmed in 24 hours.
Onion can also be grown by direct seedling. For this method, soil is thoroughly pulverised and made free of clods. 12 to 15 kg/ha seed is sown by broadcasting in band 30 cm apart during September–October in the plants. Seeds are drilled shallow in raised beds during February to June in hills area.
A light irrigation is given immediately after sowing. The subsequent watering should be done after very 10 days. When the plants are 6 to 8 weeks old of pencil size, they may be thinned 5 cm each way.
To meet the demand of green onion for salad in early winter, planting of bulbs are practices. Bulbs are dibbled 15 cm on the side of 45 cm ridges or in beds. There is also the practice of dibbling bulbs in furrows made with country plough and the field irrigated after forming beds and channels.
To plant one hectare, 750 kg of medium sized bulbs are required. Large sized bulbs, if planted, tend to flower early and result in low yields. Medium sized bulbs obtained from a seedling–planted June crop can also be utilized for planting in October, after giving a month rest.
Sets are small size onions produced by allowing the seedlings to mature in the nursery bed as such instead of transplanting them as usual. These small bulbs are used as sets.

Fertilization
A proper amount of nutritional elements in the soil favors not only the productivity but also the quality and shelf life of the product. In general, the organic fertilization is not recommended because it can affect the shelf life of the bulbs and encourage attacks by nematodes and fungal pathogens. For the family crops and hobby level is appropriate for the manure or compost made ​​are ripe. At the professional level the organic fertilizer is made ​​on the crop that precedes the onion in the rotation, making 40-50 t/ha of manure.
The major requirements of nitrogen occur in the period from seed germination to bulbification. The needs for an average production of 30t/ha are around 100-150 kg / ha of nitrogen, which is distributed in part before transplantation and in part on the roof. Although the administration of nitrogen causes considerable production increases, contributions late compromise the shelf life of the bulbs. A nitrogen deficiency due to reduction of the size of the plants, leaves stiff consistency and light green in color with yellow quotes. The nitrogen will be distributed partly in pre-sowing and part in coverage with 2-3 interventions from 30-50 kg/ha, the first of which when the plant has reached a height of 4-5 cm.
Requests for phosphorus and potassium are more in the 20 days prior to harvest. Phosphatic and potassium fertilization takes place before the transplant the bulbs with 150-200 kg/ha of phosphorus and 100-150 of potassium. These fertilizers are to be distributed in part to the soil preparation and in part together with the nitrogen sowing. They are best fertilizers containing calcium as calcium nitrate and sulfur as potassium sulphate and superphosphate mineral simple. The presence of a high amount of sulfur in the soil contributes to increase the substances that give the classic onion flavor and which are responsible to induce tears.

Irrigation
The reduced root growth makes the onion very sensitive to water stress . Given the high susceptibility to root rot , however, the water supplies must be frequent and of limited scope. During the first weeks of development are recommended irrigation of 100-200 m3/ha, then move on to 300-400 m3/ha during the enlargement of the bulb. In total, for the entire growing cycle is required 800 - 2500 m3 of water, depending on the environment and the climate. Generally by sprinkling water supplies are lates, suspending them 25-30 days before harvest or when 20-25% of the leaf is lying on the ground spontaneously. Additional contributions, in fact, it may damage the shelf life of the bulbs.
It is useful to explore the practical concepts now shown, through the analysis of the water requirements of onion, in which to consider the assessments of water requirements and irrigation, the efficiency of irrigation, hydrological characteristics of the soil, the technical elements of the irrigation (volume of irrigation intervals, round of irrigation intervals).

Water requirements and 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 radical 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 (lowering of the dry aroma and flavor characteristic of "dressing" of the bulb).

Assessments of water requirements and irrigation
To assess the water requirements of a crop must calculate or estimate the potential evapotranspiration of reference. The reference potential evapotranspiration ( ETP0 ) is water evaporated from the soil and transpired by a crop of graminaceous (Festuca arundinacea) thick , covering it evenly , completely , in excellent sanitary conditions and water availability, of considerable extent.
It is intuitive as the evapotranspiration is a dynamic process that depends on the insolation, the temperature, the air humidity, the wind and that the ETP0 in other words represents the demand for water from the atmosphere to a system plant - ground theoretical reference.
There are different ways to measure or estimate the ETP0, more or less precise and/or complex, but the system easier and more widespread as the water is evaporated from a evaporimeter Class A (bath with standard features to be installed at a site representative of a given area basis) in each almost all the agro-meteorological stations spread in our region.
The evaporated (EV expressed in mm) must be multiplied by an appropriate "vegetation coefficient" (Kv) to bring the evaporation from the free surface of water at the reference potential evapotranspiration. This is obviously lower, on average by about 20%, for which the Kv is around 0.8.
It follows that: ETP0 = EV x 0.8
If in a given day, for example, has been registered a 5 mm is evaporated will ETP0 had a 4 mm (5 mm x 0.8).
Any one crop during the crop cycle is not always covers the ground completely and not always the foliage is uniformly developed or developed as that of the reference culture described in the definition of ETP0 in other words the highest potential evapotranspiration of a culture (ETPC) can be significantly different from ETP0 mainly as a function of the characteristics of the leaf and the stage of development . E ' for this that have been developed for " crop coefficients " ( Kc ) that vary from crop to crop depending on the stage of development ( phenological phases ) which, multiplied by the ETP0 , give the maximum potential evapotranspiration of the crop:

ETPC = ETP0 x Kc


For a crop of onions sown directly in the field crop coefficients for the different phenological phases are those shown in Table 3.

Table 3 - Crop coefficients (Kc) of a long day onion to spring planting.
Code Phenological Phase Duration in days Kc
1
2
3
4
5
From emergency up to 4 leaves
Since 4 leaves up to early bulbification
During the enlarged of the bulb
For the entire collapse of the leaves for 0-20% of plants
Since the collapse of all the leaves of the 20% of the plants, until the harvest
30
30
60
10
20
0,50
0,70
0,95
0,70
0,00
Total cycle 150 -


Knowing for the periods indicated on the reference potential evapotranspiration is possible to calculate the potential evapotranspiration of the onion crop and with simple sum that of the whole crop cycle which represents the water requirement of the crop.
Obviously, the water requirement of the crop is hardly equal to the irrigation requirement, that the water to distribute with the irrigation to satisfy the water demand of the onion crop. This is because there exist a "natural flows" of water (water supply useful soil, rainfall, capillary rise from the water aquifer and ground-water level), because the irrigation system has always inefficiencies and why it is sometimes necessary to distribute more water than needed for the crop.
Natural flows: in the calculation of irrigation requirements we are considered for each period: It is obvious that for the calculation of water requirements and the values of ​​ETP0, of reliable rainfall, useful rainfall to the water reserves of the soil must be properly considered from multi-year data (historic series). From the above, it follows that:

Net irrigation requirements = Irrigation requirements - Natural contributions of water


Efficiency of irrigation
In function of the irrigation system, not all the water should be distributed regards the soil volume explored by the roots of the crops. In other words, the irrigation systems have different efficiency (Table 4). For example, with the irrigation rain system, about 20-25% of the water distributed can fail, purpose for which the net irrigation requirements must be appropriately increased.


Table 4 - Efficiency of irrigation systems.
Irrigation system Efficiency (%)
Infiltration lateral from grooves
Sprinkling (rain irrigation)
Localized (drop irrigation)
0,50-0,60
0,75-0,80
0,90-0,95


In our environments the onion crop is irrigated with sprinklers sprinkling especially for retracting or with low pressure sprinklers on movable wings. It is important that the intensity of the rain is not high in order to avoid that the beating effect causes the enticement of the apparatuses foliar.
An example of the calculation of the water requirements for onion crop sown in March and irrigated with sprinkler system is shown in Table 5.

Table 5 - Example calculation of the water requirements of an onion crop sown in March, with a cycle of 153 days and watered by sprinkling.
Phenological phase (code) (1)
Month March April May June July August Total
1 1 2 2 3 3 3 4 5 5 -
Time (days) (2) 21 10 20 10 21 30 10 10 11 10 153
crop coefficient (3)
ETP0 (mm al giorno) (4)
ETPc (mm al giorno) (5)
ETP0 (mm/periodo) (6)
Reliable rainfall (mm/time) (7)
Useful rainfall (mm/time) (8)
Net irrigation requirements (mm/time) (9)
Efficiency of irrigation (10)
Field irrigation requirements (mm/time) (11)
0,5
2,0
1,0
21,0
40
40
0

0
0,5
2,5
1,3
12,5
20
20
0

0
0,7
2,5
1,8
35,0
40
40
0

0
0,7
3,0
2,1
21,0
15
15
6,0
0,8
7,5
0,95
3,0
2,9
59,9
15
15
44,9
0,8
56,1
0,95
4,0
3,8
114,0
0
0
114,0
0,8
142,5
0,95
5,0
4,8
47,5
0
0
47,5
0,8
59,4
0,7
6,0
4,2
42,0
0
0
42,0
0,8
52,5
0
6,0
0
0
0
0
0
0,8
0
0
6,0
0
0
0
0
0
0,8
0



352,9


254,9

317,9
(1) It is the code assigned to the phenological stage of the corresponding crop coefficient Kc;
(2) Time interval has elapsed since the previous observation in the context of the month;
(3) Kc detectable from the table of crop coefficients as a function of phenophase;
(4) It is obtained by multiplying the EV evaporated in mm for the tank coefficient (equal to 0.8);
(5) It is calculated by multiplying the crop coefficient Kc for ETP0 point = (3) x point (4);
(6) It is calculated by multiplying the ETPC (expressed in mm/day ) for the time (in days) = point (5) x point (2);
(7) They are those which have the probability of at least 80% of occurrence in a given time;
(8) They are in practice those measured using a pluviometer or common pluviograph;
(9) It is calculated as the difference between the ETPC (expressed in mm/day) and the effective rainfall (expressed as mm/time) = point (6) - point (8);
(10) It is the water that reaches the roots and it is a tabular value in relation to the irrigation system;
(11) It is obtained by dividing the net irrigation requirements (mm/time) for the efficiency of irrigation that is point (9)/point (10).


Taking in consideration the budget shown in Table 5, should be done some important general considerations:
  1. Immediately after sowing or transplanting in reality it is always good to keep the soil moist to encourage the emergence or the rooting of seedlings. The seed of onion, in fact, has a good capacity to blend water even in seemingly dry land, but because the germination proceeds regularly requires abundant moisture. It is for this reason that in crops sown, if the weather does not permit, irrigation after sowing must be accurate in order to ensure, consistent with the thermal regime, rapid and regular emergencies. The maintenance of a surface layer of the soil constantly moist is particularly important in loamy soils which tend to form a surface crust.
  2. The phase of enlargement of the bulb (step 3) is the that presenting the major irrigation requirements and the greater susceptibility to water stress causing the decrease in the size of the bulbs with an increase of the population showing the lowest sizes of the bulbs and loss of yield and marketable production.
  3. About 20 days before harvest irrigation should be suspended so as to avoid delay of the maturation phase, the deterioration of the product's shelf life and increasing of the bad bulbs with damages of the tunics.
From the example shown in Table 5, the water requirement is approximately 353 mm (= 3,530 m3/ha) and the irrigation requirements of field about 318 mm (= 3,180 m3). If the crop was irrigated with a localized system (drip irrigation) with an efficiency of about 90% (= 0.9) the irrigation requirements of field would be 282 mm (= 254 mm/0.9 ).
Calculations of this type give us a reliable estimate of water consumption of the crop throughout the cycle and allow you to identify peak periods (phase of enlargement of the bulbs).
This balance may also be performed on a daily basis in a culture in place by placing the values ​​of potential evapotranspiration, the natural flows (rainfall) and following the development of the crop.
These data, together with those relating to the hydrological characteristics of land allow us to calculate the main technical elements of irrigation.

Hydrological characteristics of the soil
The two most important hydrological characteristics of the land are the "field capacity" and "wilting point".
The field capacity is the maximum water content that can contain the ground without the spaces that are occupied in charge of the circulation of air (macroporosity). When these spaces are occupied by water the soil is said saturated and therefore asphyxiated and unbearable for the plant.
The wilting point is instead the water content of the soil below which the plant is no longer able to absorb water and then fades.
The amount of water between the field capacity and the wilting point is called the "available water".
These hydrological characteristics are strongly dependent on soil texture (Table 6): the more soil is clay, the higher its capacity for water retention or, in other words, the higher the water available that is able to store in the layer explored by the roots of the crop.

Field capacity, wilting point and available water (% water by volume) of soils with different texture.
Soil Weaving Capacity of field
(% by volume)
Wilting point
(% by volume)
Water available
(% by volume)
Sandy
Sandy-silty
Silty-sandy
silty
silty-clayey
Medium-textured
Clayey
2,6
6,9
9,2
12,7
18,4
24,4
45,9
1,8
4,2
5,2
6,3
6,3
14,3
26,0
0,8
2,7
4,0
6,4
8,4
10,1
19,9


The exact determination of the constants hydrological requires a laboratory analysis of soil samples of each plot or of homogeneous areas from the standpoint of soil . To say that a clay soil at field capacity was about 20% by volume of water available is to say that on a layer of 1 meter, it contains a 2,000 m3 of water per hectare (10,000 m2 x 1 mx 0,20 = 2.000 m3 = 200 mm ) .
Technical elements of irrigation
Volume of irrigation intervals. It is the quantity of water (expressed in m3 or in mm) which must be distributed to each irrigation operations to bring the soil at field capacity ( ideal state ) . The crop should be irrigated before they actually consume all the water available, i.e. before they reach the wilting point with impaired full productive potential. Depending on the culture and its characteristics, so there is a "critical limit intervention" that is intermediate between the field capacity and wilting point. This limit determines the useful fraction of a percent of the water, the water that is readily usable by the crop, which once consumed must be made with the volume of irrigation intervals.
Onion in the water is easy to use 30% of the available water.
To calculate the available water and that can be easily used by the crop in a given soil must also take into account the layer of soil that the root system is able to explore. In the onion depth considered is 0.35 m . For the calculation of the volume of irrigation intervals must also take account of the efficiency of irrigation because the lower the efficiency, the more water must deploy to bring the soil at field capacity , net of losses . From what exposed on the formula of the volume of irrigation intervals (V ) for the onion is the following:

V ( m3) = [water available %/100) x 0.3 x 10,000 m2 x 0.35 m]/irrigation efficiency


example: If a medium-textured soil, clayey water has profit equal to 15 % by volume (= 0.15) and the onion has a depth of 0.35 m of the root end, the critical threshold equivalent to 30 % water useful (= 0.3) and the irrigation system is a system adopted in the rain (80% efficiency = 0.8), the volume of irrigation intervals will be:

V = (0.15 x 0.3 x 10,000 m2 x 0.35 m)/0.8 = 196.9 m3 ≈ 20 mm.


Turn of irrigation. Defines the interval in days between one watering and the next. It is easily identified when all the water used by the crop was consumed by evapotranspiration. You should keep a water balance where the incoming there is the water reported with the irrigation, to the net of the efficiency of the irrigation system, and that of the useful rainfall fall and in exit the daily consumption of the crop evapotranspiration (ETPC). It irrigates when the "proportional balance" is next to zero. In the onion in the spring-summer cycle, given the low water volumes, the irrigation shifts are usually short and low rainfall delay the irrigation turn of some days.
In the case of localized irrigation is maintained constantly near the soil at field capacity by adopting, therefore, very low volumes of irrigation intervals and shifts very narrow (even daily) .

Culinary uses
Onions are often chopped and used as an ingredient in various hearty warm dishes, and may also be used as a main ingredient in their own right, for example in French onion soup or onion chutney. They are very versatile and can be baked, boiled, braised, grilled, fried, roasted, sautÚed or eaten raw in salads. Their layered nature makes them easy to hollow out once cooked, facilitating stuffing them. Onions are a staple in Indian cuisine, often used as a thickening agent for curries and gravies. Onions pickled in vinegar are eaten as a snack. These are often a side serving in pubs and fish and chip shops throughout the United Kingdom and The Commonwealth, often served with cheese and/or ale in the United Kingdom. In North America, sliced onions are battered and deep fried and served as onion ring. The onion rings are a form of hors d'oeuvre or side dish commonly found in the United States, Canada, United Kingdom, Ireland, Australia, and some parts of Asia. They generally consist of a cross-sectional "ring" of onion (the circular structure of which lends itself well to this method of preparation) dipped in batter or bread crumbs and then deep fried; a variant is made with onion paste. Whole onion rings make for better presentation through a variety of sizes, while those made from a paste offer quantity through consistent size. Consumers of whole onion rings run the risk of pulling the onion out of the batter if they fail to cut it all the way through with their teeth; onion rings made of onion paste break apart easily, while oil absorbency diminishes the onion taste. Onion rings are sometimes dipped into ketchup or spicy sauces.

Onion Genome
Onion is one of the most important vegetable crops in the world and, although its importance, can be considered an “orphan crop” as it has received little attention from researchers compared to the other monocot species like rice, maize and wheat.
Plant pathology and molecular information useful for improving the existing breeding programs inside the species are lagging behind major commercial crops, mainly because the onion genome is too complex to sequence or characterize.
Allium cepa L. (2n=16) is a biannual allogamous plant, with a very large nuclear genome (16.5 Gbp per 1C, ~ 6X larger than rice and maize), characterized by a high presence of repeated sequences and a low GC content (32%) compared to any other angiosperm.
A strong maternal influence has also been observed in the species, but few studies are nowadays available to clarify the molecular mechanisms underlying this effect.
Too study the maternal effect on a number of agronomic traits in onion is very important.
Due to the high heterozygosity of the species, several Double Haploids (DH) lines were produced from onion genotypes contrasting for photoperiod sensitivity and bulb colour. This allowed us to greatly reduce allelic variation at each locus and thus simplify data analyses, besides the evaluation of maternal effects on different traits. First of all, the tolerance to Fusarium oxysporum f. sp. cepae (FOC), a common soil fungus and the causal agent of the basal rot of onion, that severely affects onion production in the open field and bulbs storage in stock, was studied through an accurate physio-pathological tests in order to understand heritability and penetrance of the trait.
The tests aimed to characterize all DH lines for their tolerance to FOC at the beginning of plant development in order to identify lines with a different behaviour for the host-pathogen interaction.
Interesting results were found during the evaluation and a DH line with optimal tolerance and two DH lines with an high susceptibility to the pathogen were identified. This has allowed us to cross these lines with each other to derive reciprocal F1 and RF1 progenies useful to assess the maternal effects by comparing their behaviou"r to that of the parent lines against to the fusariosis.
At the same time, field trials were set up and plants were phenotyped for several important agronomic traits of epigeal part such as: growth rate, leaf erectness, leaf waxiness, leaf crancking.
Same type of phenotyping has been conducted for the bulb, so it has been annotated number of dry skin, dry skin retention, dry skin color, bulb firmness.
In a complementary study, bioinformatic approaches were applied to identify in silico a set of candidate genes orthologous of major determinants for important developmental traits (i.e. photoperiod sensitivity and vernalization requirements) in model and crop species.
Plants of specific F1, RF1 and their parental lines with contrasting genotypes has been used in a screening for DNA polymorphisms in candidate genes in order to find informative SNPs among the different onion typology.
The origin of DH lines used for this analysis was cv "Cipolla di Tropea" (Red Short Day Onion), cv "Bianca di Pompei" (extra early White Short Day Onion), a common commercial Hybrid (Red Long Day Onion) and a "Density" typology (Yellow Long Day Onion ).
Moreover, the global methylation status of the genome was derived in the same material, using the methylation-sensitive amplified polymorphism (MSAP) technique to quantify different levels of methylation.
The information obtained during this project will be useful in onion breeding because it will allow to design a program taking in account the maternal effect and better exploit the potential of the plant material used by the breeders.
Onion has a huge amount of DNA, more than six times the amount of humans. This enormous amount of DNA has hindered efforts to sequence the onion’s DNA and develop genomic resources for this economically important specialty crop.
Pilot sequencing of the onion DNA revealed very low gene densities and long tracts of repetitive DNA, which indicates that widely used approaches to genome sequencing would be inefficient and expensive.
To get around this obstacle, researchers reduced the frequency of redundant DNA by selecting against DNA with an additional methyl group attached. Methylated DNA tends to be repetitive in plant genomes.
NIFA-funded researchers at the University of Wisconsin, The J. Craig Venter Institute, and partner institutions have completed pilot sequencing of random and methyl-filtered DNA fragments from one highly inbred onion population.
Their results indicate that methyl-filtration of onion DNA was very effective in reducing the proportion of both self-replicated (transposons) and anonymous sequences, and identified increased non-organellar proteins.
These results are the highest so far reported for any plant and indicate that sequencing of methyl-filtered DNA fragments is an efficient approach to mapping the enormous onion genome.
This research was supported by a NIFA Initiative for Future Agricultural and Food Systems grant and was published in October 2008 in the journal Molecular Genetics and Genomics.

Nutrients and phytochemicals
Most onion cultivars are about 89% water, 4% sugar, 1% protein, 2% fibre and 0.1% fat. They contain vitamin C, vitamin B6, folic acid and numerous other nutrients in small amounts. They are low in fats and in sodium, and with an energy value of 166kJ (40 kcal) per 100 g (3.5 oz) serving, they can contribute their flavour to savoury dishes without raising caloric content appreciably.
Onions contain phytochemical compounds such as phenolics and flavonoids that basic research shows to have potential anti-inflammatory, anti-cholesterol, anticancer and antioxidant properties. These include quercetin and its glycosides quercetin 3,4'-diglucoside and quercetin-4'-glucoside.
There are considerable differences between onion varieties in polyphenol content, with shallots having the highest level, six times the amount found in Vidalia onions, the variety with the smallest amount. Yellow onions have the highest total flavonoid content, an amount 11 times higher than in white onions. Red onions have considerable content of anthocyanin pigments, with at least 25 different compounds identified representing 10% of total flavonoid content.
Some people suffer from allergic reactions after handling onions. Symptoms can include contact dermatitis, intense itching, rhinoconjunctivitis, blurred vision, bronchial asthma, sweating and anaphylaxis. There may be no allergic reaction in these individuals to the consumption of onions, perhaps because of the denaturing of the proteins involved during the cooking process.
While onions and other members of the genus Allium are commonly consumed by humans, they can be deadly for dogs, cats, guinea pigs, monkeys and other animals. The toxicity is caused by the sulfoxides present in raw and cooked onions which many animals are unable to digest. Ingestion results in anaemia caused by the distortion and rupture of red blood cells. Sick pets are sometimes fed with tinned baby foods and any that contain onion should be avoided. The typical toxic doses are 5 g (0.2 oz) per kg (2.2 lb) bodyweight for cats and 15 to 30 g (0.5 to 1.1 oz) per kg for dogs.

Eye irritation
Chopping an onion causes damage to cells which allows enzymes called alliinases to break down amino acid sulfoxides and generate sulfenic acids. A specific sulfenic acid, 1-propenesulfenic acid, is rapidly acted on by a second enzyme, the lachrymatory factor synthase (LFS), giving syn-propanethial-S-oxide, a volatile gas known as the onion lachrymatory factor or LF. This gas diffuses through the air and soon reaches the eye, where it activates sensory neurons, creating a stinging sensation. Tear glands produce tears in order to dilute and flush out the irritant.
Eye irritation can be avoided by cutting onions under running water or submerged in a basin of water. Leaving the root end intact also reduces irritation as the onion base has a higher concentration of sulphur compounds than the rest of the bulb. Refrigerating the onions before use reduces the enzyme reaction rate and using a fan can blow the gas away from the eyes. The more often one chops onions, the less one experiences eye irritation.
The amount of sulfenic acids and LF released and the irritation effect differs among Allium species. In 2008, theNew Zealand Crop and Food institute created a strain of "no tears" onions by using gene-silencing biotechnology to prevent synthesis by the onions of the LFS enzyme.

Diseases
Peronospora scheildenii - Mildew of the onion. Sporangiophores and sporagia (Figure 13) and diseased plantlets of onion (Figure 14).

Figure 13 - Sporangiophores non-septate, various shades of violet, emerging from stomata, 122-150 Ám long, 7-18 Ám wide at their base, tapering to acute sterigmata at tips, 2-6 times monopodially branched, bearing 3-63 sporangia. Sporangia pyriform to fusiform, attached to sporangiophore by pointed end, 18-29 x 40-22 Ám, thin-walled, slightly papillate at proximal end, germinating by 1 or 2 germ tubes. Mycelium non-septate, intercellular, 4-13 Ám. Haustoria filamentous, coiled within cells, 1,5-5 Ám diam. Oogonia 43-54 Ám diam. Oospores often numerous, globular, 30-44 Ám diameter.



Figure 14 - On onion leaves, elongated, faintly yellowish lesions on the inner and outer side of leaves, covered by greyish-violet down, leaf tips shrivel, drying up of leaves, beginning with the older and outer leaves and progressing to young leaves until the entire plant may be killed. On seed stalks, similar lesions, especially on the upper part, often causing twisted or lopsided stalk growth. Death of leaf and stalk tissue frequently hastened by secondary infection by Alternaria porri. Seed transmission has never been demonstrated although flower parts are infected. Oospores, even when present in the soil in large numbers, do not appear to carry the mildew from one season to the next. However, onion bulbs infected by mycelium may give rise to systemically infected plants which serve as primary foci for disease outbreak. Bulbs of other cultivated and wild species of Allium may also harbour the pathogen. Sporulation is heaviest at 13 ░C and 100% relative humidity, it ceases below 80% RH and 7 ░C and above 25 ░C. Sporangia germinate well over a wide temperature range (7-25 ░C); germination requires the presence of free moisture or relative humidity close to 100% and, at 15 ░C, takes only 3 hours. Sporangia survive under dry conditions for several days. Germ tubes penetrate through stomata. Infection takes place between 4 ░C and 25 ░C. In a dry season, when disease development depends on dew and irrigation, outbreaks are favoured by dense stands, rows running perpendicular to the direction of prevailing winds and overhead sprinkling. In Eastern Europe, a method for predicting the intensity of outbreaks has been worked out, which is based on the amount of mycelium overwintering in bulbs; if the incidence of mildew is high on bulbs maturing late in one autumn, then the amount of mycelium carried over is large and the intensity of mildew outbreaks in the next year's crop can be predicted to be high. Cultivars differ greatly in susceptibility, but none are completely immune. Freedom from mildew of seed bulbs, bulblets and transplants is essential. Where outbreaks are severe, dense stands must be avoided. Overhead sprinkling is the least desirable mode of irrigation. Fungicides based on copper and carbamates are effective, if applied frequently enough, and the addition of stickers often improves control.



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