Assessment of Trait Dynamics for Selection under Terminal Heat Stress in Bread wheat (Triticum aestivum L.)

Abstract

Terminal heat stress is a major constraint to wheat productivity in warming environments. The present investigation was undertaken to assess genetic variability under contrasting heat regimes, examine the association of component traits with grain yield, and identify key selection traits through path coefficient analysis for improving heat tolerance in Triticum aestivum. A panel of 500 genotypes was evaluated under timely sown (TS), late sown (LS) and very late sown (VLS) conditions using an α-lattice design. Significant effects of genotype, environment and genotype × environment interaction were observed for all studied traits, indicating substantial genetic variability and strong environmental modulation. Progressive delay in sowing resulted in marked reductions in chlorophyll content, grain filling duration, grain weight, grain number and grain yield, confirming effective imposition of terminal heat stress. Correlation and path coefficient analyses revealed environment-dependent shifts in yield determination. Under TS, grain yield was primarily governed by thousand kernel weight and number of grains per spike. Under LS, the contribution of phenological and physiological traits increased, while under VLS, spike fertility emerged as the strongest direct determinant of yield, accompanied by greater influence of chlorophyll retention and early heading. The increasing residual effects under severe stress suggested greater complexity of yield expression. Overall, the results highlight the need for environment-specific selection strategies, with emphasis shifting from grain weight under optimal conditions to reproductive efficiency and stress-resilience traits under terminal heat stress.