Variability studies for yield and its components under heat stress condition in wheat [Triticum aestivum (L.)]

The rising global demand for wheat is threatened by climatic challenges such as heat stress, necessitating the identification of key yield-attributing traits for breeding stress-resilient cultivars. The present study evaluated sixty bread wheat (Triticum aestivum L.) genotypes during rabi 2023-24 at the College Farm, N. M. College of Agriculture, Navsari Agricultural University, Navsari, under late-sown heat stress conditions (December and January) in a randomized block design with two replications. Twenty-three morphological and physiological traits were recorded, including phenological, yield, and stress-related parameters. Analysis of variance revealed highly significant differences among genotypes for all traits, indicating wide genetic variability. Phenotypic coefficients of variation (PCV) were marginally higher than genotypic coefficients of variation (GCV), reflecting environmental influence, with canopy temperature depression (CTD) at anthesis and 15 days after anthesis exhibiting the highest variability and thus strong potential for selection. Grain filling rate, biological yield, and grain yield per plant displayed moderate GCV and PCV, suggesting their suitability as selection targets. High heritability coupled with high genetic advance was observed for grain filling rate (December sowing) and for biological yield and CTD (January sowing), highlighting the predominance of additive gene action and minimal environmental effects. Traits such as effective tillers per plant, harvest index, chlorophyll content, NDVI, and grain yield also showed moderate to high heritability with moderate genetic advance, indicating good scope for improvement. In contrast, plant height, spike length, and grains per spike exhibited low heritability and genetic advance, limiting direct phenotypic selection. Overall, the study identifies CTD, grain filling rate, biological yield, and grain yield as key traits for breeding heat-tolerant wheat genotypes under late-sown stress conditions.