Fine genetic mapping of the white immature fruit color gene w to a 33.0-kb region in cucumber (Cucumis sativus L.)

The white immature fruit color gene w was rapidly mapped to a 33.0-kb region to identify a valuable candidate gene that encodes peroxidase. The skin color of immature fruit is a crucial external trait of cucumbers, and white skin is shared by limited numbers of commercial cultivars. Herein, one BC1 population and two F-2 segregating populations were constructed using four inbred parental lines (WD3 x B-2-2 and Q30 x Q24) to investigate the inheritance patterns and chromosomal locations of immature fruit color genes in cucumbers. Consequently, a single recessive gene, w, was identified that controls white immature fruit color. A total of 526 markers, which were derived from published genetic maps, two reference cucumber genomes ("9930" and GY14), and two parents (Q30 and Q24) for which whole-genome sequence information is available, were used to map the target gene w to a 33.0-kb region flanked by two SNP-based markers, ASPCR39262 and ASPCR39229, which are physically located at 39262450 and 39229482 of chromosome 3 ("9930" draft genome assembly), respectively. Gene prediction indicated that four potential genes were located in the target region. One gene that encodes peroxidase is likely to be a valuable candidate gene because quantitative real-time PCR revealed an eightfold difference in its transcriptional level, and several amino acid variations were found when the deduced amino acid sequence was aligned. A co-segregating marker was used synergistically to test its ability to predict the skin colors of 83 dark green/white germplasms, and the validity of its utility in marker-assisted selection was confirmed. Fine mapping of this locus will assist in cloning the gene and in marker-assisted breeding to develop dark green/white cucumber cultivars.