Carbon loss under high night‐time temperature (HNT) leads to significant reduction in wheat yield. Growth chamber studies were carried out using six winter wheat genotypes, to unravel postheading HNT (23°C)–induced alterations in carbon balance, source‐sink metabolic changes, yield, and yield‐related traits compared with control (15°C) conditions. Four of the six tested genotypes recorded a significant increase in night respiration after 4 days of HNT exposure, with all the cultivars regulating carbon loss and demonstrating different degree of acclimation to extended HNT exposure. Metabolite profiling indicated carbohydrate metabolism in spikes and activation of the TriCarboxylic Acid (TCA) cycle in leaves as important pathways operating under HNT exposure. A significant increase in sugars, sugar‐alcohols, and phosphate in spikes of the tolerant genotype (Tascosa) indicated osmolytes and membrane protective mechanisms acting against HNT damage. Enhanced night respiration under HNT resulted in higher accumulation of TCA cycle intermediates like isocitrate and fumarate in leaves of the susceptible genotype (TX86A5606). Lower grain number due to lesser productive spikes and reduced grain weight due to shorter grain‐filling duration determined HNT‐induced yield loss in winter wheat. Traits and mechanisms identified will help catalyze the development of physiological and metabolic markers for breeding HNT‐tolerant wheat.

Exposure to temperatures ≥30°C during flowering and grain filling stages can negatively affect seed set and seed weight in spring wheat (Triticum aestivum L.). The screening of a large set of germplasm under hot wheat growing environments (Indo‐Gangetic Plain in India) led to the identification of promising heat‐tolerant genotypes. The selected set of 28 diverse spring wheat genotypes were exposed to heat stress (34/16°C day/night temperatures) for 10 d during flowering and for 30 d during grain filling to quantify genetic variability in pollen germination, photosynthesis, and yield parameters under controlled‐environment conditions. Pollen grains collected immediately at anthesis (between 0530 and 0630 h) were incubated on liquid in vitro pollen germination media. Averaged across wheat genotypes, a significant reduction in pollen germination (39.9%, P < 0.001) was recorded from plants exposed to heat stress. Heat stress for 10 d during flowering induced significant reduction in seed number (15.4 and 23.0%) and seed weight (32.3 and 34.6%) on main and primary spikes, respectively, compared with the control. Heat stress during grain filling had a more pronounced impact on seed weight (16 and 22%) than seed number (2.7 and 9.3%) in main and primary spikes, respectively. Genotypes KSG025 and KSG1214 with higher seed number, seed weight, and harvest index and appreciable pollen germination under heat stress were identified as candidate donors for simultaneously enhancing flowering and post‐flowering heat tolerance in spring wheat.

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The predicted increase in global temperatures will increase the probability of exposing sorghum [Sorghum bicolor (L.) Moench] to heat stress during critical reproductive developmental stages, such as flowering and post‐flowering periods. Greenhouse and field studies were conducted to quantify the impact of heat stress on pollen germination and other post‐flowering physiological processes affecting grain yield. Pollen collected from 24 diverse sorghum genotypes grown under greenhouse conditions were tested for their tolerance to heat stress. Using the same set of genotypes, field‐based heat tents were used to impose heat stress from booting stage to maturity. Pollen grains from field experiments were tested under three different types of heat stress combinations to identify genotypes with pollen having true heat tolerance. Heat stress induced a significant reduction in grain yield (16–73%), pollen germination (2–95%), photosynthesis (0.5–50%), and photochemical efficiency of photosystem II (1–8%) and increased thylakoid membrane damage (2–27%) compared with control conditions. Reduced grain yield with heat stress exposure was not compensated by grain weight increase. In vitro pollen germination revealed SC155 to possess true heat‐tolerant pollen, even under severe stress exposure. Macia and BTx378 recorded higher relative grain yield and pollen germination, providing opportunities for mapping genomic regions responsible for heat tolerance using currently available biparental mapping populations in RTx430 and BTx623 backgrounds, respectively.