Fine Mapping of the Tomato Spotted Wilt Virus resistance Gene, Tsw, in Capsicum

Tomato spotted wilt virus (TSWV) is an important viral disease affecting pepper production worldwide. A single dominant resistance gene to TSWV, Tsw, has been known to originate from Capsicum chinense. Tsw has been mapped on chromosome 10 in Capsicum. To perform genome-based fine mapping of the Tsw gene, approaches of mapping comparison, pooled transcriptome analysis, and genome walking were applied. Eleven SNPs tightly linked to the Tsw gene were developed using tomato and pepper whole genome sequencing databases. Among them, four SNP markers, SNP7715-1, SNP68-1, SNP17918-1, and SNP1072-1, showed no recombination in two segregating populations of F₂ ‘Telmo’ (210 individuals) and ‘SP’ (843 individuals). Three scaffold sequences from the pepper genome database and two BAC clones from the BAC library of C. annuum ‘CM334’ covering the Tsw gene were identified by transcriptome analysis and genome walking. The region of Tsw was delimited within 259 kb by alignment analysis of two BAC clone sequences and the pepper scaffold sequence. A total of 22 predicted genes were resided in the target. Among them, eight predicted genes showing annotations of NBS-LRR resistance proteins were identified in genome of C.annuum ‘CM334’. To confirm accurate sequence of candidate genes in target, eight genes were blasted to WGS of C. chinense. The homolog sequences of seven candidate genes out of eight genes were identified in C. chinense.