Identification and Mapping of bs8, a Novel Locus Conferring Resistance to Bacterial Spot Caused by Xanthomonas gardneri

Although cultivars possessing recessive resistance alleles provide effective control of bacterial spot of pepper (Capsicum annuum), the deployed resistance gene, bs5, is ineffective against Xanthomonas gardneri, one of the pathogenic species. Resistance against X. gardneri was identified in C. annuum accession PI 163192, and this study sought to characterize this novel resistance and to map the resistance gene(s) to the pepper genome. We crossed PI 163192 with the susceptible cultivar Early Calwonder (ECW) to develop resistant near-isogenic lines (NILs) of ECW, designated ECW80R. The novel resistance in ECW80R was determined to be quantitative, recessively inherited, and non-hypersensitive-response causing, and inhibits lesion expansion and chlorosis. Presence of the resistance in NILs decreased the in planta bacterial population by ninefold compared with ECW. Bulked segregant analysis of resistant and susceptible individuals from an F₂ population using whole genome single nucleotide polymorphisms identified a major resistance locus within an approximate 6-Mbp interval on the subtelomeric region of chromosome 11. We developed markers spanning this region and used these to genotype backcross F₂ populations, which further delimited the resistance locus within a 2.3-Mbp interval. The novel resistance locus has been designated bs8. ECW80R and the linked markers developed in this study should prove useful for breeders seeking to advance this resistance into commercially relevant germplasm and for pyramiding bs8 with other resistance alleles such as bs5 and bs6. The allele bs8 will help prolong the durability of bacterial spot resistance in pepper and improve resistance to multiple species of Xanthomonas.