Quantifying the effect of high temperature stress on critical developmental stages in rice

The predicted increase in the intensity and frequency of global heat waves posess a serious threat to sustained rice productivity under current and future climates. Temperatures exceeding critical thresholds during sensitive developmental stages will lead to reduced yield and poor grain quality. To have a comprehensive understanding of the effect of high temperature stress on critical developmental stages, seven diverse genotypes from different ecological groups were tested under high temperatures during the panicle initiation, microsporogenesis, anthesis, and early grain-filling stages. Different sets of plants were used for each treatment and upon identification of the target developmental stage, plants were exposed to six hours (0830 to 1432h) of high temperature (39 deg C) for four consecutive days. Panicle initiation stage was identified by dissection and gametogenesis by using a predetermined morphological marker. Spikelet fertility was scored at all four stages on plants exposed to both high and control (29 deg C) temperature. At anthesis, spikelets from both control and high temperature treatments were collected one hour after opening to record in vivo pollen count, pollen germination, and pollen tube growth. Seeds from the plants exposed to treatment at the early grain-filling stage were analyzed for grain quality. At gametogenesis stage, IR2006 recorded the highest fertility followed by N22, whereas the panicle initiation stage was unaffected by high temperatures. N22 recorded significant high spikelet fertility at anthesis, which can be attributed to its high pollen viability and maintenance of pollen tube growth compared with other genotypes. Spikelet fertility at early grain-filling stage was unaffected, while high temperature stress decreased amylose content and increased gelatinization temperature and chalkiness. Quantifying the effects of high temperature on different developmental stages will form the basis for further genetic and molecular analysis of high-temperature tolerance.