Botanical improvement of varieties-general characters of Indian varieties and the application of genetics to rice improvement

Indian rices belong to the indica group of Oryza sativa Linn. They are characterised by wide diversity in their morphological and physiological characters. They vary in duration from 85–200 days, in their adaptability to different climatic conditions from cultivation at sea-level to that, at an altitude of 4,000–5,000 feet. They vary in their adaptability to growing in different seasons of the year, and in growing under upland and deep water conditions. They also vary in their resistance to diseases, insect pests and drought. They exhibit wide variation in plant height, tillering, stiffness of straw, grain shedding habit, panicle length, size of grains as well as distribution of pigment on plant parts. The main problem in rice is the production of high yielding varieties and about 445 improved varieties giving 12–20 per cent. enchanced yield have been evolved in different States by introduction, selection in natural populations and hybridization. Other problems which have received attention at the hands of rice breeders are the evolution of early maturing varieties; varieties responsive to heavy manuring; non-lodging and non-shedding varieties; varieties resistant to floods, salinity, drought, diseases and insect pests, as well as varieties with profuse tillering habit and higher milling out-turn. In all the above breeding projects the principles of heridity, variation and genetic recombination as well as the principle of differential response of genotypes under different environmental conditions, have been fully utilised for the improvement of the rice crop, and several varieties have been evolved or are in the process of evolution, to meet the different requirements