Multi-location and multi-year evaluation of wheat germplasm lines for terminal heat stress tolerance in major wheat growing zones of India

Terminal heat stress, caused by elevated temperatures during critical reproductive stages, poses a major challenge to wheat production in India. This study evaluated 200 wheat germplasm lines under normal (timely-sown) and late-sown (heat-stressed) conditions across multi-location and multi-year trials to assess their agronomic performance and heat tolerance. Significant reductions in key traits, including grain yield, germination percentage, ground cover, days to flowering, and thousand-grain weight, were observed under heat-stressed conditions. Specifically, grain yield decreased from an average of 4.45 t/ha in normal-sown conditions to 3.01 t/ha under heat stress, reflecting the profound impact of elevated temperatures on wheat productivity. Conversely, canopy temperatures increased significantly during critical growth stages under terminal heat stress. Notably, eight genotypes (IC449061, IC470134, IC28029, IC279878, IC584159, IC396586, IC416146, and IC335683) demonstrated superior performance, indicating their potential for breeding heat-tolerant varieties. The findings emphasize the importance of region-specific breeding strategies, optimized agronomic practices, and molecular tools to mitigate the adverse effects of terminal heat stress. This research contributes valuable insights into improving wheat resilience and securing food production in the face of climate change.