Research Review on Onion (Allium cepa L.) in Iran

Onion is one of the main vegetable crops in the world and each year different local and
foreign genotypes of onions are grown in Iran. Because of many morphological, physiological, cultural and biological differences among these genotypes and their interaction with environmental factors, studies of various onion traits are useful for solving problems related to onion growing in Iran. The results of researches showed that landraces and cultivars have high genetic diversity in relation to vegetative characteristics, yield, and bulb quality. Also, there are high correlations between some of these characteristics that are important for easy selection in breeding programs. The results of breeding researches showed that average yield of polycrossed genotypes is higher than inbred genotypes. Average bolting was higher in seed sowing and lower in seedling transplanting. From various irrigation methods, drip irrigation was better than furrow and basin irrigation in crop production. Use of organic manure increased yield, but the extent of yield increase depended on the chemical composition of the manures and their effects on the physical and chemical properties of the soil. Storage of onion is a way of controlling onion prices. Storage period is related to the number of tunics, the amount of tunic's adherence to scales, the diameter of onion neck and percentage of dry matter.