ONION

Introduction and importance
Onion (Allium cepa L) is one of the important condiments widely used in all households all the year round. Onions are used in soups, sauces and for seasoning foods. The small bulbs are pickled in vinegar. Onion bulb is rich in phosphorus, calcium and carbohydrates.

Trends, area, production and yield
Onion is an important crop in all continents with world production of about 25 million tonnes. There has been a progressive increase in area and production of onion in Pakistan. In 2004-05, the area increased to 127.8 thousand hectares, production 1764.9 thousand tonnes and yield was 13.8 tonnes/ha. The data since 1999-00 are as follows.

Table - 1: Area, production and yield of onion in Pakistan (1999-00 to 2004-05)

The average shares of the provinces in the over all area and production of onion, based on the data of 2004-05, are given in the following table.

Table -2: Shares of provinces in area and production of onion (2004-05)

Varieties
Onion varieties vary in colour, shape, flavour and keeping quality as well as in limit of physiological maturity. Sariab Red and Chiltan-89 are commercially grown varieties of onion in Balochistan. The red skin cultivars are comparatively more pungent with good keeping quality for storage. These varieties can also be used as green bunching onion if harvested at the proper stage. The other varieties grown in the country are Phulkara, Swat-I, Desi Red, Thana Bola Khan and Ghotki.

Table 3. Planting and harvesting times of onion

Manuring and Fertilizing
Although onion has limited root system but is very responsive to manures and commercial fertilizers. Well-rotten farmyard manure @ 10 tonnes per acre should be ploughed down at the time of land preparation at least one month before land preparation. Before transplanting 3 bags of super phosphate, one bag of ammonium sulphate and one bag of potassium sulphate per acre should be thoroughly mixed in the soil. This should be followed with a supplementary dose of one bag of ammonium sulphate per acre one month after planting. Another dose of one bag of ammonium sulphate may be applied at the time of bulb formation.

Harvesting and curing
Onion bulbs should be harvested at appropriate stage of maturity. After 50 percent of the crop showing neck fall, the onions may be lifted out of the soil. Bulbs should be left on the surface of the ground for field curing until tops are fully dry. Generally, 3-4 days of warm and dry weather for field curing is desirable to improve the storage life of onion.

Storage
Storage is likely to lead to loss instead of gain unless onions are properly handled and cured and is free from diseases. Cultivars with more dry matter content tend to be long storing types. Onions should be stored at a temperature as near 0 0C as possible and the relative humidity maintained at about 65 percent with good air circulation through the piles.

Insects
Onion thrips
Onion thrips (Thrips tabaci) are small, yellowish sucking insects, which feed on the foliage of onion plants. Thrips are most injurious during dry weather. Spraying with appropriate insecticide at weekly interval on the plants has given excellent control.

Diseases
Downy mildew
The downy mildew of onion (Peronospora destructor) is a fungal disease of onion grown in cool moist conditions. In humid weather, fungus develops as white or purplish downy growth over the leaf surface but in dry weather, only white spots are seen. Dithane M-45 or any other copper based fungicide can be used to control the disease.

Purple blotch
Purple blotch (Alternaria porri) is a serious fungal disease of onion that occurs at temperature range of 25-30 0C with 70-90 percent relative humidity. The leaves and flower stalks show whitish flecks with purple colour centre, which on further development form dead patches. Spray the crop with Dithane M-45 at fortnightly interval before appearance of the disease. Keep the crop free from the weeds.

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