Impact of elevated temperature at different phenological stages on the growth and yield of wheat and rice

In this study we have evaluated the response of two cultivars of wheat (PBW-343 and Kundan) and rice (PS-2 and P-44) to high temperature stress. The stress was given either throughout crop growth period or at one of the three growth phases viz., seedling to panicle initiation, panicle initiation to flowering and flowering to maturity. Results indicated that the warmer temperature hasten crop development, shortens the growth period and thus finally lowers the grain yield in both crops. The impact of high temperature on crop growth and yield is largely determined by the duration and coincidence of it with sensitive crop growth phase. Period from panicle initiation to flowering stage was found to be more sensitive to high temperature stress in both wheat and rice. Exposure to high temperature from seedling stage to panicle initiation stage affected yield predominantly due to associated tiller mortality and reduced number of spikes. Coincidence of high temperature stress with panicle initiation to flowering phase of crop affect grain yield by reducing dry matter accumulation, productive tillers, number of spikes, grain weight and increased floret sterility. When the crop is exposed to heat stress from flowering to maturity, then the reduction in yield is predominantly caused by floret sterility leading to reduced number of grains per spike and also due to reduced grain weight. Among the varieties, Kundan of wheat and PS-2 of rice were found to be more tolerant to heat stress.