Genetic Variability, Broad-Sense Heritability, and Trait Associations of Bread Wheat (Triticum aestivum L.) Across Multiple Environments in Kenya

Aims: This study evaluated phenotypic variation and genotypic differences, estimated broad-sense heritability for grain yield, and examined associations among agronomic traits in five bread wheat (Triticum aestivum L.) genotypes comprising two parental cultivars and three mutation-derived lines. Study Design: Randomised complete block design with three replications. Place and Duration of Study: The genotypes were evaluated at Kitale, Eldoret, and Njoro, Kenya, during the 2021 and 2022 long-rain seasons, representing six environments. Methodology: Seven agronomic traits were analysed using descriptive statistics, combined analysis of variance, restricted maximum likelihood estimation of variance components, entry-mean broad-sense heritability, and Pearson correlation analysis. Results: Grain yield ranged from 1.80 to 3.50 t ha⁻¹, with a mean of 2.70 t ha⁻¹. Genotype significantly affected all evaluated traits, demonstrating differentiation among the wheat materials, while environmental effects varied among traits. Grain yield was significantly influenced by genotype, location, and season, with a significant genotype × location interaction indicating differential genotypic responses across locations. For grain yield, genotypic variance (σ²G = 0.018) exceeded residual variance (σ²e = 0.012) and genotype × environment interaction variance (σ²GE = 0.006). Entry-mean broad-sense heritability was high (H² = 0.91), indicating strong repeatability of differences among genotype means under the multi-environment testing framework. Grain yield was moderately and positively associated with thousand-kernel weight (r = 0.42), while days to maturity was moderately and negatively associated with thousand-kernel weight (r = −0.53). Days to heading and days to maturity were moderately and positively correlated (r = 0.42). Conclusion: The relatively large genotypic variance and high entry-mean heritability indicate that the evaluated materials could be reliably differentiated for grain yield across the testing framework, although environmental and interaction effects remained relevant. Integrating replicated grain-yield performance with genetic parameters and complementary agronomic traits, particularly thousand-kernel weight, provides a sound basis for identifying promising parental and mutation-derived materials for advancement in bread wheat improvement.