Phenotypic diversity, genotype × sowing date interaction, and multi-trait selection of wheat ( <i>Triticum aestivum</i> L.) genotypes under contrasting dates of sowing in the mid-Terai of Nepal

Wheat (Triticum aestivum L.) production in Nepal is frequently constrained by delayed sowing due to the late rice harvest, leading to terminal heat stress during critical reproductive stages. In this context, this study was conducted using an alpha-lattice design with two replications and 50 genotypes comprising 49 indigenous landraces and one improved check variety (Vijay) across three sowing dates (November 25, December 5, and December 15) at the Agronomy Research Farm, Agriculture and Forestry University, Chitwan, Nepal, during the 2024-2025 growing season. The study aimed to evaluate phenotypic diversity, genotype × sowing date interaction (GEI), and multi-trait selection. Analysis of variance revealed highly significant (p < 0.001) genotypic effects for phenological, morphological, and yield traits, alongside significant GEI for grains/plant, thousand-grain weight, spikes/plant and grain yield. Delayed sowing progressively shortened crop duration by up to 10.27 days. Although mean grain yield declined numerically by 39.2% from DOS1 to DOS3, the main effect of sowing date on grain yield was not statistically significant (p = 0.07). MGIDI identified NGRC09199 as superior across all sowing dates. These findings support timely sowing as an essential agronomic strategy and provide a foundation for heat-adaptive wheat improvement in Nepal.