Genetic diversity analysis of wheat under timely, late and very late sowing conditions

Heat stress is a major constraint in wheat (Triticum aestivum L.) production, especially when sowing is delayed. The present study assessed the genetic divergence among 30 spring wheat genotypes under three sowing times namely, timely sown, late sown and very late sown, which corresponds to increasing terminal heat stress. Mahalanobis D² analysis was used to group genotypes into different clusters and quantify divergence at each sowing time. The analysis revealed the formation of 10 clusters under timely sowing, 11 clusters under late sowing and 7 clusters under very late sowing. Cluster composition varied with sowing time, with many genotypes forming unique singleton clusters under optimal conditions, whereas under severe heat stress most genotypes grouped together, indicating a convergence of performance under stress. The highest inter-cluster distance was observed under late and very late sowing suggesting greater genetic divergence in heat-stressed environments. Cluster mean analysis showed significant differences for agronomic and quality traits. Under late and very late sowing, Cluster V in late, Cluster II in very late sowing exhibited superior mean grain yield per plant along with higher tiller number and grains per spike, reflecting better heat tolerance. In contrast, clusters comprising heat-susceptible genotypes had much lower yields and poor yield components. Trait contribution to divergence also shifted with sowing time: under timely sowing, grain Fe content was the single largest contributor to total divergence (33.6%), whereas under late and very late sowing, grain Zn content contributed most (20.2% and 29.4%, respectively), followed by grain yield and grain weight. The results indicate substantial genetic diversity among the wheat genotypes for traits associated with heat stress adaptation. Heat-tolerant genotypes were distinct in cluster analysis, possessing traits like early maturity, higher tillering, and better grain-filling under stress. The diverse genotypes can be harnessed in breeding programs to improve wheat terminal heat stress tolerance.