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Dull/glossy fruit skin is a highly valuable external quality trait that affects the market value of cucumbers. In this study, genetic analysis showed that one single dominant gene, D (dull fruit skin), determines the dull fruit skin trait in cucumber. By combining bulked segregant analysis with 11 published polymorphic molecular markers on chromosome 5, the D/d gene was preliminarily mapped between markers SCZ69 and SSR16203, at genetic distances of 0.3 and 0.6 cM, respectively. Subsequently, a larger F2 (S06 × S94) population (842 individuals in total) was used for high-resolution mapping of the D/d gene. Finally, the D/d gene was fine-mapped between markers SSR37 and SSR112, at a physical distance of 244.9 kb (containing 31 candidate genes), using eight newly developed polymorphic simple sequence repeat (SSR) markers between SCZ69 and SSR16203. Based on semi-quantitative RT-PCR analysis, the possible candidate gene D was identified as Csa016880 or Csa016887. Meanwhile, validity analysis of the markers SSR37 and SSR112 was performed with 72 dull/glossy fruit lines, and showed that the two co-dominant SSR markers could be used for marker-assisted selection of the dull/glossy fruit trait in cucumber breeding. Moreover, this study will be helpful for cloning of the D gene in cucumber.

Powdery mildew is one of the most important diseases of cucumber (Cucumis sativus L.). For many years, researchers have studied and attempted to isolate resistance genes for this disease for breeding powdery mildew-resistant cucumber. In this study, bulked segregant analysis and an initial quantitative trait loci (QTLs) analysis based on a local linkage map were performed using an F2 population. A major locus on the long arm of chromosome 5 was identified for powdery mildew resistance and named pm5.1. For fine mapping of the pm5.1 locus, BC3F1 and BC2F2 populations that segregated only at the target genomic region were developed by marker-assisted selection. The location of the pm5.1 locus was confirmed by QTL analysis using a subset of the BC3F1 population and was delimited in a 1.8-cM interval between flanking markers UW065011 and UW065190. Using the large BC3F1 (n = 480) and BC2F2 (n = 483) populations, pm5.1 was mapped to a ~170-kb region between markers UW065021 and UW065094. Based on the annotations for the genes in this region, a MLO-like gene was identified as the most likely candidate for the pm5.1. Sequence alignment analysis of the MLO-like genes from susceptible and resistant cucumber lines revealed two types of mutations in this candidate gene that may result in recessive resistance to powdery mildew in the resistant cucumber lines.