Characterization of a late blight resistance gene homologous to R2 in potato variety Payette Russet

Abstract

Breeding for late blight resistance has traditionally relied on phenotypic selection, but as the number of characterized resistance (R) genes has grown, so have the possibilities for genotypic selection. One challenge for breeding russet varieties is the lack of information about the genetic basis of resistance in this germplasm group. Based on observations of strong resistance by Payette Russet to genotype US-23 of the late blight pathogen Phytophthora infestans in inoculated experiments, we deduced the variety must contain at least one major R gene. To identify the gene(s), 79 F1 progeny were screened using a detached leaf assay and classified as resistant vs. susceptible. Linkage mapping using markers from the potato SNP array revealed a single resistant haplotype on the short arm of chromosome group 4, which coincides with the R2/Rpi-abpt/Rpi-blb3 locus. PCR amplification and sequencing of the gene in Payette revealed it is homologous to R2, and transient expression experiments in Nicotiana benthamiana confirmed its recognition of the Avr2 effector. Sequencing of a small diversity panel revealed a SNP unique to resistant haplotypes at the R2 locus, which was converted to a KASP marker that showed perfect prediction accuracy in the F1 population and diversity panel. Although many genotypes of P. infestans are virulent against R2, even when defeated this gene may be valuable as one component of a multi-genic approach to quantitative resistance.