Identification of SNPs linked to eight apple disease resistance loci

Abstract

Although genetic and genomic studies have progressed to a very advanced level in apple, the application of this acquired knowledge for marker-assisted breeding (MAB) remains limited mainly to pyramiding monogenetically inherited resistances against apple scab, powdery mildew and fire blight. Crucial contributing reasons are the uncertainty in map position of some genes and the lack of tightly linked markers suitable for high-throughput analysis (HTA) that reduces the costs of MAB. Single-nucleotide polymorphism (SNP) markers have the potential to resolve these major issues. Here we present the refined map positions of the apple scab resistance genes Rvi2, Rvi4 and Rvi11, and the systematic search for SNPs associated with apple scab (Rvi2, Rvi4, Rvi6, Rvi11, Rvi15), powdery mildew (Pl2) and fire blight (FB_E and FB_MR5) resistances. With the aid of the ‘Golden Delicious’ sequence, several SNPs linked to each of the eight resistances were identified in the genomic regions around the resistance loci previously delimited by simple sequence repeat markers. The specificity of the alleles in coupling with the resistances was determined by screening eight apple genotypes, six of them being founding clones of modern apple cultivars. These SNPs can now be used to develop SNP-based HTA assays for MAB.