SELECTION FOR REPRODUCTIVE STAGE DROUGHT AVOIDANCE IN RICE, USING INFRARED THERMOMETRY

Water deficits cause major yield reductions on the world's rainfed ric eland. The most severe water deficits occur during the reproductive ph ase. Differences in canopy temperature among crop cultivars are known to be related to drought avoidance characters, In developing a practic al field screening system for reproductive phase drought resistance in rice (Oryza sativa L.), we assessed the canopy temperature response o f a range of germplasm, and related the results to other plant charact ers related to drought resistance, Field experiments were conducted on a silty clay loam Typic Hapludoll at the International Rice Research Institute, Planting of the test cultivars was staggered, to synchroniz e flowering during the water-deficit period, Canopy temperature measur ements were made on 12 dates in Trial 1 and 8 dates in Trial 2. Mean c anopy temperatures (T-c) increased from 28 to 37 degrees C during the stress period, Grain yield (r(2) = -0.63*) and spikelet fertility (r( 2) = 0.51*) were related to midday T,on the day of flowering, Highly significant differences were observed in canopy temperature among entr ies, with low coefficients of variation (2.0-2.7%), Entries with a his tory of outstanding vegetative stage drought screening scores consiste ntly remained coolest under stress, Visual drought tolerance scores (r = 0.72*) and leaf rolling scores (r = 0.68**) were correlated with m ean canopy temperatures under moderate water stress, but not under sev ere stress (r = 0.31NS; r = 0.21NS). Infrared thermometry was judged w ell-suited to monitor the progression of crop water stress development , and to aid in classifying cultivars for relative drought avoidance. However, caution is necessary to assure proper application of the tech nique and in data interpretation.