Mapping of a novel locus Ra conferring extreme resistance against potato virus A in cultivated potato (Solanum tuberosum L.)

Abstract

Potato virus A (PVA) is one of the major viruses affecting potato worldwide, and can cause serious disease symptoms and yield losses. Previously, we determined that potato cultivar Barbara harbors Ry_sto (genotye: Ryryryry) and Ra (genotype: Rararara) that each independently confers extreme resistance (ER) to PVA. In this study, employing a combination of next-generation sequencing and bulked-segregant analysis, we further located this novel Ra on chromosome 4 using a tetraploid BC₁ potato population derived from a Ry-free progeny (Rararararyryryry) of Barbara (RarararaRyryryry) × F58050 (rararararyryryry). Using 39 insertion-deletion (InDel) spanning chromosome 4, Ra was delimited by the Indel markers M8-83 and M10-8 within a genetic interval of 1.47 cM, corresponding to a 1.33 Mb genomic region in the potato DM reference genome. The InDel marker M10-8, which displayed 99.3% agreement with the phenotypic results in the Ry-free segregating populations, was then used to screen 43 tetraploid potato cultivars and breeding clones. An overall correlation of 76.6% between the marker and phenotype was observed. These findings obtained above are of importance in furthering the cloning of Ra and employing the marker-assisted selection for PVA resistance.