Evaluating Genetic Variation and the Potential for selection in Growth and Yield Characteristics of Wheat (Triticum aestivum L.) Genotypes.

Wheat (Triticum aestivum L.) is a critical component of global food security, but its productivity is under growing pressure from environmental factors, notably terminal heat. Understanding the genetic architecture of morpho-physiological features is critical for creating robust, high-yielding cultivars. This two-year study, conducted during the Rabi seasons of 2023-24 (Talwandi Sabo, optimal conditions) and 2024-25 (Ongole, simulated heat stress), evaluated 43 different wheat genotypes to assess genetic variability, heritability, character associations, and genetic divergence for key morpho-physiological, yield, and quality parameters. Field research used a Randomized Block Design (RBD), whereas laboratory assessments of seed vigor and protein content used a Completely Randomized Design (CRD). The analysis of variance revealed significant ( P <  0.01) differences among genotypes for all sixteen field traits (including days to 50% flowering, plant height, flag leaf area, spike characteristics, yield components, and test weight) and ten laboratory traits (including germination percentage, seedling vigor indices, and protein content) under both optimal and heat stress conditions, indicating significant genetic variability. High heritability, combined with high genetic advance as a percentage of the mean, was observed for critical traits such as flag leaf area (97.42%, 77.84% GAM under optimal), biological yield per plant (93.77%, 73.71% GAM under optimal), number of grains per spike (97.74%, 104.81% GAM under stress), and protein content (94.29%, 26.57% GAM in 2023-24 lab), indicating the dominance of additive gene action and selection. Correlation and route coefficient analyses revealed that biological yield per plot and test weight were the most significant direct positive contributors to grain yield under optimal conditions, but spike components (number of grains, grain weight) became increasingly important under heat stress. Genetic divergence (D ² ) study separated genotypes into six groups under ideal conditions and five under heat stress, with significant inter-cluster distances indicating the possibility of heterotic combinations. Traits such as number of grains per spike and test weight were significant drivers to divergence. Heat stress increased phenology while reducing most yield-related traits. Stress tolerance indices identified genotypes HD 2307, PBW 677, HD 3386, and PBW 165 as potentially heat-tolerant. This study provides a solid genetic foundation for selecting superior parental lines and devising breeding strategies for wheat varieties with higher yield, quality, and resilience to a variety of environmental conditions, especially terminal heat stress.