Agronomic Variation and Stem Rust Response in M 4 Gamma-Irradiation-Derived Bread Wheat (Triticum aestivum L.) Lines
Abstract
Induced mutagenesis can broaden variation available for crop improvement, but the breeding value of mutation-derived materials depends on their performance in advanced generations. This study evaluated 64 M4 gamma-derived bread wheat (Triticum aestivum L.) lines, together with their parental varieties, Njoro II and Chozi, for stem rust response, yield per spike, and 1000-kernel weight. The entries were evaluated in a randomised complete block design with three replications. Stem rust severity was assessed at Zadoks growth stages GS65, GS77, and GS85, and disease progression was quantified using the area under the disease progress curve (AUDPC). Genotype effects were significant (p < 0.001) for all measured traits. AUDPC ranged from 100 to 1520 %-days, while yield per spike and 1000-kernel weight ranged from 0.80 to 2.20 g and 17.07 to 38.89 g, respectively. Dunnett-adjusted comparisons showed that all 30 Njoro II-derived and 34 Chozi-derived lines recorded significantly lower AUDPC than their respective parents. Eighteen Njoro II-derived and 20 Chozi-derived lines combined significantly lower AUDPC with significantly higher yield per spike and 1000-kernel weight relative to their respective parents. AUDPC was negatively correlated with yield per spike (r = −0.859) and 1000-kernel weight (r = −0.877), while yield per spike and 1000-kernel weight were positively correlated (r = 0.938) (p < 0.001). The results showed variation in stem rust development and the two assessed yield-related traits, with some lines combining lower disease development with higher yield per spike and 1000-kernel weight relative to their respective parents. These lines provide candidates for continued evaluation rather than evidence of established disease resistance or agronomic superiority. Further testing across generations and environments, together with assessment of grain yield and a broader range of agronomic traits, will be necessary to determine the consistency and breeding relevance of the observed performance.