First Report of Genomic Regions Associated With White Leaf Spot Resistance in <i>Brassica napus</i>

ABSTRACT White leaf spot, caused by the fungal pathogen Neopseudocercosporella capsellae , is a re‐emerging disease of canola ( Brassica napus ), as its incidence and severity have increased over recent years. The disease primarily affects leaves but can also infect stems and siliques, and has resulted in considerable yield losses, particularly in Australia. Despite this, there is limited research into genetic resistance and no white leaf spot resistance quantitative trait locus (QTL) or resistance genes have been reported in any Brassica species. In this study, we identify genomic regions associated with white leaf spot resistance based on genome‐wide association studies (GWAS) conducted on a panel of 215 B. napus genotypes. The genotypes were screened for both cotyledon and leaf resistance, and displayed varying levels of resistance ranging from highly susceptible to completely resistant. GWAS identified five genomic regions, one on chromosome A07, two on chromosome A09 and three on chromosome C04, that were associated with either cotyledon or leaf resistance. Putative resistance genes within these regions were identified and can be further investigated. This is the first study to map genetic resistance for white leaf spot and offers initial insights into the genetic basis of resistance. The identified regions can be targeted in breeding programmes to bolster white leaf spot resistance in elite germplasm.