Learn about Rice is one of the most important cereals in the world. Most people in Asia and tropical and subtropical countries use rice as a major staple food. Almost all cultivated rice plants belong to Oryza sativa L., which was originated in Asia, and which is divided roughly into two subspecies, Indica and Japonica. Between these two typical subspecies, rice is differentiated into many kinds of ecotypes according to local conditions. Each ecotype has a different response to day length, temperature, soil fertility, and water supply. Accordingly, different ecotypes of rice are cultivated in a manner corresponding to the soil properties of the paddy fields, growth seasons, climatic conditions, and methods of cultivation.