High‐Temperature Stress During Reproductive Stages: Impacts and Traits Associated with Seed Set

Abstract High temperature (HT) stress negatively influences reproductive phases in field crops, and the effects are critical to understand in the present and future climate. This review focuses on research on grain crops (rice, wheat, sorghum, pearl millet, soybean and groundnut) with the goals of identifying (i) the sensitivity of reproductive stages during crop development under HT stress and (ii) the metabolic changes caused by HT on the reproductive tissue. Reproductive stages are the most sensitive stages in plants to stress, particularly flowering and gametogenesis, and which results in a reduction in seed numbers due to fertility loss, improper fertilization, and reduction in seed‐set percentage. Most of the field crops are sensitive to a temperature of >35 °C during the reproductive growth stages, and this threshold varies among the species and genotypes. Abortion of micro‐ and/or mega‐spores, premature tapetal cell degradation, loss of gamete viability, anther indehiscence, a lower pollen grain germination rate on the stigma, loss of pollen germination, stigma receptivity, pollen tube tip polarity, pollen tube growth signals, and embryo abortion are the physiological processes affected by HT stress. The major changes in the gametes lead to alteration in carbohydrate metabolism and transport, loss of viability, elevated reactive oxygen species production, increased membrane phospholipid saturation level and decreased phosphatidic acid level. Molecular and biochemical tools help to screen and identify the sources of tolerance. Developing crop tolerance to high‐temperature stress is possible through continued collaboration among biologists, breeders, and agronomists without affecting the crop grain yields.