QTL Mapping for Cucumber Fruit Size and Shape with Populations from Long and Round Fruited Inbred Lines

To gain insight into the molecular and genetic basis of fruit size and shape in cucumber, we conducted Quantitative Trait Locus (QTL) mapping with F2 and BC1F1 populations derived from a cross between the Northern-China type inbred line CNS21 and the Southern-China type inbred line RNS7. Populations were evaluated during two developmental stages, ovary at anthesis and commercial fruit (immature fruit). A total of 13 major-effect QTLs (R2 > 10%) were detected for six traits, and one of them, fruit shape index 2.1, explained more than 50% of phenotypic variation. All QTLs distributed on chromosome (chr) 1 and 2. We constructed a physical map containing almost all of the QTLs with their physical location from previous studies. For fruit size and shape, the highest number of QTLs were mapped on chr1 and chr6, and the fewest number were mapped on chr2 and chr7. At least one consensus region was presented on each chromosome. In addition, three candidate genes were predicted between the long-fruited and round-fruited inbred lines by comparing the sequences of the consensus region of chr3, where many QTLs for marketable fruit length had been detected. Our results provide a base for additional QTLs and molecular markers for fruit size and shape in cucumber breeding.