belonging to the genus Oryza and has two cultivated and 22 wild species. The cultivated species are Oryza sativa and O. glaberrima. O. sativa is grown all over the world while Oryza glaberrima has been cultivated in West Africa for about 3500 years. There are more than 120,000 varieties of cultivated rice. Cultivated rice is diploid (2n=24) and belong to AA genome. O. sativa has two subspecies O. sativa ssp. indica and O. sativa ssp. japonica. A less prominent intermediate O. sativa ssp. javonica is also available.