SCREENING RICE FOR DROUGHT RESISTANCE AT THE REPRODUCTIVE PHASE

Water deficits result in large yield reductions on the one-half of the world's rice land that is rainfed. The most severe water deficits ten d to occur during the reproductive stage. Field studies were conducted over a three-year period to develop a method to screen rices for repr oductive-phase drought stress resistance. Staggered planting date was effective in synchronizing the flowering of test entries during the st ress treatment period. Grain yield, relative grain yield, and spikelet fertility were significantly and negatively related to the number of days beyond the beginning of the stress period that a cultivar flowere d. A drought index based on the deviation of entry performance from re gression of the plant character on flowering date (expressed as days f rom application of the drought stress treatment) was used to adjust cu ltivar performance. Rankings were similar for the index values of the grain yield, relative grain yield, and spikelet fertility. Percent spi kelet fertility was highly correlated with grain yield in the event of reproductive-stage water stress (r2 = 0.64*, 0.84**, and 0.66** duri ng three years of tests). Spikelet fertility was judged the most pract ical character by which to score cultivar performance. A mass screenin g method is proposed that involves staggered planting, interruption of irrigation during the flowering period, visual scoring for spikelet f ertility, and regression analysis to adjust for differences in floweri ng date.