Association mapping of a locus that confers Southern stem canker resistance in soybean

Abstract

Background Southern stem canker (SSC), caused by Diaporthe aspalathi (E. Jansen, Castl. & Crous) is an important soybean disease, which has been responsible for severe losses in the past. The main strategy to control this fungus is through the introgression of resistance genes. So far, five main loci have been associated with resistance to Southern stem canker. However, there is a lack of information about useful allelic variation at these loci. In this work, a genome-wide association study (GWAS) was performed to identify allelic variation associated with resistance against Diaporthe aspalathi and to provide molecular markers useful in breeding programs. Results We characterized the response to Southern stem canker infection in a panel of 295 accessions from different regions of the world including important Brazilian elite cultivars. Using a GBS approach, the panel was genotyped and we identified marker loci associated with Diaporthe aspalathi resistance using GWAS analysis. We identified 19 SNPs associated with Southern stem canker resistance, all on chromosome 14. The peak SNP showed an extremely high degree of association (p-value = 6.35E-27) and explained a high level of the phenotypic variance (R2 = 70%). This strongly suggests that a single major gene is responsible for resistance to D. aspalathi present inn most of the lines comprising this panel. We also identified in resequenced soybean materials other SNPs in the region identified by GWAS in the same LD block that clearly differentiate resistance and susceptible accessions. The peak SNP was selected and used to develop a cost-effective molecular marker assay, which was validated in a subset of the initial panel. In an accuracy test, this SNP assay demonstrated 98% of selection efficiency. Conclusions Our results suggest a relevant importance of this locus in SSC resistance in soybean cultivars and accessions from different countries and the SNP marker assay developed in this study can be directly applied in MAS studies in breeding programs to select resistance materials against this pathogen and support its introgression.