Tolerance to low radiation during grain filling stage in rice

Low radiation is a determining factor in the development and growth of rice crop and causes yield losses in many regions of the world. We evaluate the diversity of response of rice varieties to a reduction of radiation during grain filling stage yield and yield components were measured in field experiments (two consecutive years). Shade during grain filling significantly reduced grain yield, spikelet fertility and 1000-grain weight in both experiments (dry and wet season). Phenotypic plasticity (GxE) was only observed in both experiments for spikelet filling and 1000-grain weight, suggesting differential genotypic response for these traits under low radiation. Two tolerant genotypes VANDANA and NORUNKAN and three susceptible genotypes SWARNA, ZALCHA and RAY NABJA were selected from the field experiments and studied under controlled growth chamber conditions for low radiation tolerance during the vegetative stage. Shade increased the maximum photosynthesis (A(max)) for VANDANA, suggesting a shade adapted behavior maximizing carbon gain under low radiation. However; NORUNKAN showed high Amax and the lowest light compensation point (LCP) and respiration under control and shade conditions suggesting a double strategy to maintain carbon (maximize gain and reduce carbon loss under low radiation conditions). This study demonstrates that targeting photosynthetic traits to maximize carbon gain and reduce carbon loss under low radiation conditions is a strategy that should be explored to increase rice tolerance to low radiation conditions during grain filling stage.