Growth and grain yield of contrasting rice cultivars grown under different conditions of water availability

Rice crops are susceptible to drought, which causes large yield losses in many Asian countries. The development of drought resistant cultivars may be assisted if mechanisms of drought resistance are known. This work was carried out to elucidate how some rice cultivars achieve higher yield than others under water-limiting conditions. A total of 11 experiments were conducted in northeast Thailand, and four contrasting cultivars were compared in each experiment for phenological development, dry matter growth, leaf death, grain yield and yield components. High-yielding cultivars were generally short statured and had high harvest index, and they tended to perform better than others in all conditions of water availability, When drought developed during late growth stages, early flowering to escape water stress was an important character. During late drought some cultivars were able to retain green leaves longer than others and increased dry matter when others stopped growing. It is thus concluded that cultivars suitable for rainfed conditions are those with high yield potential resulting from high harvest index under favourable growing conditions, appropriate flowering time to escape severe water stress that commonly develops after the end of the rainy season, and an ability to maintain growth during drought so that yield determining processes can be completed with minimum disturbance.