Effect of High Temperature during Heading and Early Grain Filling on Grain Yield of Indica Rice Cultivars Differing in Heat-Tolerance and Its Physiological Mechanism

Abstract

Heading/flowering and early grain filling are the most stress-sensitive periods in rice growth and development. However, little is known how heat-stress during these periods affects the yield formation. This study investigated pollen development, yield components and some physiol. parameters under high temperature treatments during heading and early grain filling. Four indica rice cultivars, Shuanggui 1 and T219 (heat-sensitive), Huanghuazhan and T226 (heat-tolerant), were pot-grown and subjected to high temperature treatments (the mean temperature during the day > 33°C) during heading/flowering (0-10 d after heading) and early grain filling (11-20 d after heading), and the natural temperature (the mean temperature during the day < 30°C) was taken as the control. The results showed that the high temperature treatment significantly reduced pollen and spikelet fertility rate in heat-sensitive cultivars, and not in heat-tolerant cultivars as compared with the control. Seed-setting rate was significantly decreased under the high temperature for heat-sensitive cultivars, leading to a significant reduction in grain yield, with a more reduction under the treatment during heading than during early grain filling. It was less affected for heat-tolerant cultivars. The heat-stress treatment significantly increased activities of enzymes involved in antioxidant system in leaves for the heat-tolerant cultivars, while it much less affected for heat-sensitive cultivars. The high temperature significantly reduced ATPase activity in grains for the heat-sensitive cultivars, and the result was reversed for the heat-tolerant ones. The high temperature increased leaf-temperature and malondialdehyde content in leaves, and reduced root activity and the photosynthetic rate of the flag leaf for both kinds of cultivars, but the increase or reduction was less for heat-tolerant cultivars than for heat-sensitive cultivars. These results suggested that lower leaf-temperature, higher root activity, higher ATPase activity in grains, and higher photosynthetic rate and activities of antioxidant enzymes in leaves would be important physiol. traits leading to a higher grain yield for a heat-tolerant rice cultivar.