ABSTRACT
Rice (Oryza sativa L.) is an important food crop which was grown on a land area of more than 155 million hectares worldwide in 2008 (USDA, 2009). Rice is one of the oldest cultivated crops on earth. It also is probably the world’s most versatile crop that grows at more than 3000 m elevation in the Himalayas and at sea level in the deltas of the great rivers of Asia. Floating cultivars grow in water as deep as 4 m in Thailand, and in Brazil, rice is grown as a dryland crop much like wheat or corn. In West Africa, rice is grown in mangrove swamps. Rice, like barley (Hordeum vulgare L.), oats (Avena sativa L.), rye (Secale cereale L.), and wheat (Triticum aestivum L.), belongs to the Gramineae family. It was ‰rst domesticated about 10,000 years ago; however, its exact origin of domestication is not known. The domestication of rice could have occurred independently at several places in a broad belt from the foothills of the Himalayas to Vietnam and southern China (Chang, 1975). The geographical dispersal and the selection pressures of farming led to a large number of varieties of O. sativa, the Asian species. Another species, Oryza glaberrima, was later domesticated in western Africa (Hargrove, 1988). Rice is the staple food crop in the diet of about one-half of the world’s population; it provides 35%–60% of the dietary calories consumed by nearly 3 billion people (Fageria et al., 2003). More than 90% of the world’s rice is grown and consumed in Asia, where about 60% of the world’s people live. Rice is also a staple food in Latin America, parts of Africa, and the Middle East. China and India are the largest producers and consumers of rice in the world.
