Mass screen for drought tolerance at seedling stage in rice

Conditions and parameters for drought tolerance mass screen at seedling stage, reliably identifying tolerant and susceptible rice varieties, were established. Susceptible IR64 and PSB Rc82, and tolerant varieties, PSB Rc14, KDML 105, NSIC Rc9, along with 65 test genotypes, were evaluated in paddy soil-filled galvanized iron trays. With intermittent stress, water was withheld 14 days after seeding (DAS) and re-watered 21 days from saturation (DFSat) followed by second withdrawal 53 DAS up to 21 DFSat. With moderate and severe stress, water was withheld for 26 and 31 DFSat, respectively. Control plants were grown in fully watered tray. Leaf-rolling and leaf tip drying of susceptible varieties ensued at 9 and 4 DFSat, with corresponding soil moisture content (SMC) of 32.9 % and 21.4%. Tolerant varieties manifested leaf-rolling and drying 11 and 14 DFSat, with 27.3% and 21.4% SMC, respectively. Highest seedling recovery of 34% and 36% from moderate and intermittent stress, respectively, was observed in PSB Rc14. Severe stress resulted in death of most plants. Flowering delay of 24-41 days was observed across varieties under moderate stress, with longest delay in late maturing KDML 105. With intermittent stress, susceptible varieties delayed flowering longer, 93-99 days, than tolerant varieties, 78-82 days. Panicle production under moderate stress was reduced by 60% in susceptible, and 30%-44% in tolerant varieties. Susceptible varieties incurred greater reduction in biomass, spikelet fertility and grain yield. PSB Rc14 was most tolerant to stress, followed by KDML 105 and NSIC Rc9, while PSB Rc82 was more susceptible than IR64. Comparing the responses of the test genotypes with IR64 and PSB Rc14, 39 of 65 (60%) entries were classified tolerant to drought. Drought tolerance screen at seedling stage is useful for target environments having water deficits early in the cropping season.