High-resolution mapping of zym, a recessive gene for Zucchini yellow mosaic virus resistance in cucumber.

KEY MESSAGE: Using a high-resolution mapping approach, we identified a candidate gene for ZYMV resistance in cucumber. Our findings should assist the development of high-versatility molecular markers for MAS for ZYMV resistance. Zucchini yellow mosaic virus (ZYMV) causes significant disease, which leads to fruit yield loss in cucurbit crops. Since ZYMV resistance is often inherited recessively in cucumber, marker-assisted selection (MAS) is a useful tool for the development of resistant cucumber cultivars. Using 128 families of an F2:3 population derived from a cross between susceptible 'CS-PMR1' and resistant 'A192-18' cucumber inbred lines, we confirmed that ZYMV resistance is conferred by a single recessive locus: zym (A192-18) . We constructed a cucumber genetic linkage map that included 125 simple sequence repeat (SSR) markers segregating into 7 linkage groups (chromosomes). The zym (A192-18) locus was mapped to chromosome 6, at genetic distances of 0.9 and 1.3 cM from two closely linked SSR markers. For high-resolution genetic mapping, we identified new molecular markers cosegregating with the zym (A192-18) locus; using cucumber genomic and molecular marker resources and screening an F2 population of 2,429 plants, we narrowed down the zym (A192-18) locus to a <50-kb genomic region flanked by two SSR markers, which included six candidate genes. Sequence analysis of the candidate genes' coding regions revealed that the vacuolar protein sorting-associated protein 4-like (VPS4-like) gene had two SNPs between the parental lines. Based on SNPs of the VPS-4-like gene, we developed zym (A192-18) -linked DNA markers and found that genotypes associated with these markers were correlated with the ZYMV resistance phenotype in 48 cucumber inbred lines. According to our data, the gene encoding VPS4-like protein is a candidate for the zym (A192-18) locus. These results may be valuable for MAS for ZYMV resistance in cucumber.