Onion - an important vegetable crop

Allium cepa (Onion) is a very common vegetable of our daily use for the preparation of curry or salad. It is a wonderful vegetable, which would have been a fruit if it is not been pungent and full of sulphur ingredients.
It is a vegetable that is fat free. According to the food and Agriculture Organisation, about 5.5 million acres are sown every year yielding a crop (bulb) of 38 million tonnes. It is grown over more than in 160 countries of the world.
The leading onion producing countries are India, China, USA, Turkey, Japan, Iran etc. Pakistan produces only 1.40 million tonnes in 2001. At present, the area under crop is about 47,000 acres.
The average yield comes to about 11.5 tons/hectare. The average onion consumption comes to about 6 kg per person per year in the country. However, Turkey has the highest onion per capita consumption with an astounding 38 kg each year.
Fresh onion consumption has risen by 55% over the last 20 years from 5.5 kgs per person in 1980 10.0 kgs per person in 2000. Onion is a vegetable of all seasons. It usually comes in three colours: yellow, red and white. It is used to enhance the flavour and taste in a curry.
The onion's smell is pungent and can cause tears in the eyes. The onion's flavour, odour and tear characteristics come primarily from the sulphuric compounds in the vegetable.
Onions provide health-promoting phytochemicals as well as nutrients which contain antioxidant compounds known as quercetin that help delay or slow oxidative damage to the cells and tissues of the body.
Studies have shown that it also helps eliminate free radicals in the body, to enable low-density lipoprotein oxidation to protect and regenerate vitamin E and to inactivate the harmful effects of chelate metal ions.
Onions are free from fat and sodium, and contain 5% carbohydrate and 13% dietary fiber. One onion contains 60 calories. Onions are also a good cure for a bad cold. It is a very popular folk medicine for fevers and cold.
The ancient Egyptians worshipped onions and wore onion garlands to keep them safe from bacteria. Patients with high fever and cold were treated with hot onion soup.
Other studies have shown that the consumption of onion may be beneficial for the reduced risk of certain diseases and may prevent gastric ulcers. It is also considered as a blood thinner and platelet inhibitor.
The onion is one of the most important bulb crops and is also an important vegetable crop, grown commercially in all parts of the world. The demand of onion is world-wide, this is the only reason that onions are found in most of the markets of the world throughout the year.
The onion is probably a native of Asia. There are over 300 species of onion. The crop is grown as an annual and is propagated most frequently by seeds sown directly in the field.
Onions may also be grown from transplants started in greenhouses or outdoor seedbeds or from small bulbs, called sets grown from the previous years.
Field spacing varies: plants are generally grown 1-4 in (2.5-10 cm) apart in 14-18 in (36-46 cm) rows. Onion varieties are classified mainly according to pungency (milder or pungent) and use (dry bulbs or green bunching). Bulbs maybe white, red or yellow.
The onion is by far the most important of the bulb crops and also has great significance among vegetable crops because of its year-round consumption. The onion is used for consumption both in the green state and as mature bulbs. Onions are used as salad and cooked in various ways in all curries, fried, boiled, used in soup making, in pickles and for other purposes.
Onion belongs to the family Amaryllidaceae and the genus Allium. Small-sized onions are more nutritive.
The onion is a basic kitchen item in India and Pakistan and also in other countries of the region including Bangladesh and Sri Lanka which imported Pakistani onion last year, 95 percent of Pakistan's onion is absorbed in Sri Lanka alone.
In Pakistan, onion is grown the year around in all the four provinces, though the Sindh province produces half of the total onion which is used for both local consumption and export.
In 1997-98 onion was sown on over 77,900 hectares which increased by 2.2 percent by 79,100 hectares in 1998-99. The yield also registered a similar increase from almost 1.1 million tonnes to 1.12 million tonnes during the same period.
The onion season in the two primary producing provinces - Sindh and Balochistan runs from November to March and May to October, respectively. Onion is propagated by seed.
The harvesting of dry-bulb varieties usually starts after the leaves begin to turn yellow and fall, generally 3-4 months after planting. Bulbs to be harvested are cured by exposure to warm dry air.
Bulbs onions are best adapted to production in subtropical and temperate areas. Onions are sometimes harvested as bulbs and others as green shoots. It is grown in nearly all cool regions.
In 1981, the world growing area of onion was estimated at 1,604x103 ha with an average yield of 12,329 kg per ha.
The area of onion is about 81.4x103 ha, with production of 1076x103 tonnes with the average yield of nearly 12-17 mt/ha. Onion production center around the Punjab and Sindh provinces, although significant production is also obtained from NWFP and Balochistan, by extending its production season.
Although its area has increased by about 80 percent, but yield ha. remained static at 9-11 mt/ha.
This compares most unfavourably with the normal yield of 35 tonnes/ha obtained in some major onion producing countries such as UK and Holland. Low productivity in the country means that unit production costs are very high making exports difficult in the highly competitive world market.
While in Punjab the area is 21x103 ha, with production of 226x103 m.ton and yield 12.5 mt/ha. In the Sindh area it is nearly 33.5x103 ha, with a production of 430 tonnes and an average yield of 12.9 mt/ha.
Sindh provides a major share of the crop and surplus stocks are being exported to encourage the growers.
In NWFP the area is 6.3x103 ha, with production of 90x103 tons and yield 14.4 ton/ha. While, in Balochistan the area is 29xl03 ha, with production of 310 tonnes and yield of 6 ton per hectare. Onion takes about 100 to 110 days from sowing to harvesting throughout the country.
The onions and its relatives are subject to many diseases. The common diseases of onion are, onion smut, blight, downy mildew, pink rot, white rot, basal rot, neck rot V and smudge.
Some diseases that occur in the field effect the yield, quality or both, others are important in stage and transit. Onion diseases cause millions of dollars in damages throughout the world.
Weather and other environmental conditions, cultivars susceptibility, cultural practices are also limiting factors in onion production.