Sensitivity of grain sorghum to high temperature stress during reproductive development

Sorghum (Sorghum bicolor L. Moench) grown in semiarid regions is often exposed to short periods of high-temperature (HT) stress during reproductive development. Objectives of this research were (i) to quantify the effects of short episodes of HT stress during reproductive development on physiological, growth, and yield processes of grain sorghum and (ii) to identify the stage(s) most sensitive during the reproductive development phase to HT stress. Plants of hybrid DK-28 E were grown in growth chambers at daytime maximum/nighttime minimum optimum temperature (OT) of 32/22 degrees C until 29 d after sowing. Thereafter, plants were exposed to OT or HT (40/30 degrees C) or were reciprocally transferred at 10-d intervals (10 d before flowering, 0, 10, 20, and 30 d after flowering [DAF]) from OT to HT and vice versa. Transferred plants remained in the new temperature regime for 10 d before being returned to their original temperature regime. Continuous HT stress delayed panicle emergence and decreased plant height, seed set, seed numbers, seed yield, seed size, and harvest indices but did not influence leaf photosynthesis. Exposure to short (10-d) periods of HT stress at flowering and 10 d before flowering caused maximum decreases in seed set and seed yield, and HT stress during postflowering stages (10, 20, and 30 DAF) decreased seed yield, with a larger reduction at early stages of seed development.