Genome-Wide Association Mapping of Resistance to Exserohilum Spike Blight in Wheat

Exserohilum spike blight, caused by Exserohilum rostratum, is an emerging constraint in wheat production, and improving host resistance is a sustainable strategy because the disease is governed largely by quantitative, environment-responsive loci rather than single major genes. Identifying genomic regions and biological pathways underlying quantitative resistance is therefore essential for developing durable resistant varieties. In this study, the Wheat Association Mapping Initiative spring wheat panel (n = 289) was evaluated across two contrasting Indian agroclimatic zones over two seasons. Resistance was quantified using two traits: incubation period (IP) and area under the disease progress curve (AUDPC). Significant genotype, environment, and genotype × environment interaction effects were observed for both traits (p < 0.001). IP and AUDPC were weakly correlated (r = -0.18 to 0.16), indicating that these traits represent partially distinct resistance components. Genome-wide association mapping identified 25 marker-trait associations, 13 for AUDPC and 12 for IP, with most associations showing environment dependence. Putative candidate genes highlighted defense-relevant loci, including an LRR receptor-like kinase and a WRKY transcription factor for IP, and an RGA2-like resistance gene and PHLOEM UNLOADING MODULATOR-like gene for AUDPC. These findings provide the first GWAS-based framework for E. rostratum resistance in wheat, prioritizing loci for validation and marker deployment.