Effect of High Temperature During Heading and Early Filling on Grain Yield and Physiological Characteristics in Indica Rice

To disclose the physiological mechanism of heat tolerance in rice (Oryza sativa L.), this article investigated the pollen development, yield components, and some physiological parameters of indica rice genotypes under high temperature (HT) treatment during heading and early filling stages. Two heat-sensitive genotypes, Shuanggui 1 and T219, and 2 heat-tolerant genotypes, Huanghuazhan and T226, were used in pot experiments with HT treatment (mean temperature during the day above 33ºC) and natural temperature (control) treatments from 0 to 10 d and 10 to 20 d after heading. Compared with the control, the HT treatment significantly reduced the rates of pollen and spikelet fertility in the heat-sensitive genotypes, but had no significant effects on the heat-tolerant genotypes. Seed-setting rate decreased significantly in the heat-sensitive genotypes under HT, leading to a significant reduction in grain yield. Moreover, the reductions of yield of heat-sensitive genotypes were greater in the HT treatment at heading stage (0–10 d after heading) than in the HT treatment at early grain-filling stage (11–20 d after heading). However, the heat-tolerant genotypes were in minor influence under the HT treatment. The activities of enzymes from rice leaves, which were involved in antioxidant system, significantly increased in the heat-tolerant genotypes when treated with HT, whereas they were maintained at relative high levels in the control. The ATPase activity in grains was significantly reduced in the heat-sensitive genotypes, but slightly influenced in the heat-tolerant genotypes. The high temperature increased leaf temperature and malondialdehyde content in leaves, and reduced root activity and photosynthetic rate of flag leaf in all genotypes. However, variation range was much less in heat-tolerant genotypes than in heat-sensitive genotypes. The results suggest that the relative high yield in heat-tolerant genotypes under high-temperature stress is associated with low leaf temperature, high root activity, and the high levels of ATPase activity in grains, photosynthetic rate, and activities of antioxidant enzymes in leaves.