Genomic regions associated with spot blotch resistance in elite barley breeding populations

Abstract

Spot blotch (SB), a prevalent foliar disease of barley, is caused by the hemibiotrophic fungal pathogen Bipolaris sorokiniana. Predominately occurring in humid growing regions worldwide, SB can result in yield losses of up to 30%. Genetic resistance remains the most effective strategy for disease management; however, most Australian barley cultivars exhibit susceptibility despite the previous identification of major resistance loci. This study investigates the genetic architecture underlying spot blotch resistance within an Australian barley breeding program. Resistance was assessed at both the seedling and adult growth stages using a single conidial isolate (SB61) across two consecutive years. A total of 337 barley lines were genotyped with 16,824 polymorphic DArT-seq™ markers. Two mapping approaches were employed: a single-marker genome-wide association study (GWAS) and a haplotype-based local genomic estimated breeding values (Local GEBV) approach. Both methodologies identified two major resistance-associated regions on chromosomes 3H and 7H, effective across growth stages. Additionally, the haplotype-based Local GEBV approach revealed resistance-associated regions on 1H, 3H, and 6H that were not detected by GWAS. Haplotype stacking analysis underscored the critical role of the 7H region for adult-plant resistance when combined with other resistance haplotypes, suggesting significant gene-by-gene interactions and highlighting the complex, quantitative nature of spot blotch resistance. This research confirms the presence of key resistance loci within Australian barley breeding populations, provides novel insight into the genetic architecture of spot blotch resistance, and emphasises the potential to enhance resistance through haplotype stacking and whole-genome prediction approaches.