Advances in Understanding of Physiological and Biochemical Responses of Crop Plants to High Temperature Stress.

High-temperature stress influences physiological, reproductive and yield processes in grain crops, and a comprehensive understanding of these effects is critical for evaluating the impacts on seed yield. This review focuses on selected grain crops with the goals of (a) quantifying the impact of season-long and short episodes of high-temperature stress on yield and yield components and (b) determining the sensitivity of reproductive stages of crop development to short episodes of high-temperature stress. Season-long and short episodes of high-temperature stress decreased biomass production, seed number, individual seed weight and yield of all grain crops, but the temperature threshold varied across species. High-temperatures had a negative impact on reproductive processes and resulted in lower seed yield. Plants were more sensitive to high-temperature stress during gametogenesis and flowering leading to loss of fertility, poor fertilization and decreased seed-set, resulting in fewer seeds. High-temperature stress during the post-anthesis stages decreased seed filling duration leading to decreased seed weight. Genetic variability exists for high-temperature tolerance, and emerging biochemical and molecular tools provide opportunities for rapid screening and identification of new sources of tolerance. Continued collaboration among biologists, breeders and agronomists is essential for developing strategies to combat the effects of high-temperature stress on seed yields.