Quantifying the Impact of Heat Stress on Pollen Germination, Seed Set, and Grain Filling in Spring Wheat

Exposure to temperatures >= 30 degrees 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 degrees 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.