Abstract
Sclerotinia stem rot (SSR) caused by the necrotrophic fungus Sclerotinia sclerotiorum is a major disease in rapeseed (Brassica napus) worldwide. Breeding for SSR resistance in B. napus, as in other crops, relies only on germplasms with quantitative resistance genes. A better understanding of the genetic basis for SSR resistance in B. napus thus holds promise for the genetic improvement of disease resistance. In the present study, a genome-wide association study (GWAS) for SSR resistance in B. napus were performed using an association panel of 448 accessions genotyped with the Brassica 60K Infinium® single-nucleotide polymorphism (SNP) array. A total of 26 SNPs corresponding to three loci, DSRC4, DSRC6, and DSRC8 were associated with SSR resistance. Haplotype analysis showed that the three favorable alleles for SSR resistance exhibited cumulative effects. After aligning SSR resistance quantitative trait loci (QTL) identified in the present and previous studies to the B. napus reference genome, one locus (DSRC6) was found to be located within the confidence interval of a QTL identified in previous QTL mapping studies and another two loci (DSRC4 and DSRC8) were considered novel loci for SSR resistance. A total of 39 candidate genes were predicted for the three loci based on the GWAS combining with the differentially expressed genes identified in previous transcriptomics analyses.
Highlights
The white mold fungus Sclerotinia sclerotiorum (Lib.) de Bary is a typical necrotrophic pathogen that infects more than 400 plant species (Boland and Hall, 1994; Bolton et al, 2006), including oilseed rape (Brassica napus L.), the second most important oil crop worldwide (FAOSTAT, 2015)
The accessions showed relatively small variation in flowering time (153–164 days from the sowing date to flowering), which would minimize the influence of developmental spans due to differences in flowering time among genotypes on artificial inoculation assay (Mei et al, 2012a; Wei et al, 2014)
The average lesion length in accessions with all three favorable haplotypes was significantly shorter than that of accessions with no or only one favorable haplotype, with lesion length being reduced by 24.6– 26.4% and 17.7–19.6% at 5 dpi. These results suggested that the genetic control of the Sclerotinia resistance in B. napus exhibits a largely additive effect
Summary
The white mold fungus Sclerotinia sclerotiorum (Lib.) de Bary is a typical necrotrophic pathogen that infects more than 400 plant species (Boland and Hall, 1994; Bolton et al, 2006), including oilseed rape (Brassica napus L.), the second most important oil crop worldwide (FAOSTAT, 2015). The infection of the sclerotinia pathogen to oilseed rape results in so-called sclerotinia stem rot (SSR), which can lead to serious yield losses of the crop. In China, annual yield losses of 10–20% have been attributed to SSR, reaching 80% in severely infected fields. The control of SSR relies heavily on culture practices and fungicide application. Culture practices have little effect, reflecting the wide host range of the pathogen and its capacity to survive for long periods as sclerotia. Fungicide application is not always reliable, reflecting
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