Identification of resistance sources and genomic regions regulating spot blotch resistance in Asian bread wheat ( <i>Triticum aestivum</i> L.) via genome‐wide association study

Spot blotch (SB), caused by Bipolaris sorokiniana, is a major yield-limiting disease of wheat (Triticum aestivum L.) in the warm, humid agroclimatic zones of South Asia. The development of resistant cultivars through molecular approaches offers a sustainable strategy for managing this disease. This study aimed to identify resistant genotypes and associated single-nucleotide polymorphism markers in a panel of 187 spring bread wheat lines via field-based phenotyping and genome-wide association study (GWAS). The panel was genotyped via the DArTSeq genotyping-by-sequencing platform and evaluated for SB resistance under artificially inoculated field conditions across two crop seasons (2019-2020 and 2020-2021) at Agua Fria, Mexico. Significant phenotypic variation was observed, with genotypes BGD54, IND56, and BGD55 showing high levels of resistance, indicating their potential as resistance donors. GWAS identified multiple marker‒trait associations (MTAs) linked to SB resistance, with seven stable MTAs consistently detected across years and models, located on chromosomes 3D, 5A, 3B, and 1B, and explaining 3.86%-18.17% phenotypic variance. Most of these MTAs colocalized with previously reported genomic regions for SB resistance. In silico analysis revealed candidate genes within these regions encoding potassium transporters, zinc finger proteins, glutathione S-transferases, FBD domain proteins, leucine-rich repeats, protein kinases, dirigent proteins, and cytochrome P450 enzymes. The identified stable MTAs and associated candidate genes offer valuable resources for marker-assisted selection and functional validation in wheat breeding programs targeting SB resistance.