Identification of QTLs controlling cold tolerance in cucumber (Cucumis sativus L.) seedlings

Cucumber (Cucumis sativus L.), an essential and economically important vegetable crop, is sensitive to cold stress. Cucumber seedlings exposed to extreme cold stress seriously reduce cucumber yield, however, few cold-tolerant genes have been identified yet. In this study, a 186 recombinant inbred lines (RILs) population constructed by crossing two inbred lines, cold-tolerant `CG104' and cold-sensitive 'CG37', was used to identify loci associated with cold tolerance in cucumber seedlings. Genetic analysis of the chilling injury index (CII) of the RILs population showed that cold tolerance in cucumber seedlings was quantitatively inherited. One QTL named qCT6.1 was repeatedly detected. It was delimited by two flanking markers (6SSR13741 and 6SSR19970) and explained 6.2% and 11.0% of the phenotypic variation in two different experiments, respectively. Furthermore, the qCT6.1 was delimited to a 271.99 kb region (flanking markers Indel8 and Indel9) using 1500 F-2 individuals, containing 41 annotated genes. Via sequence and expression analysis, we speculated that CsaV3 6G042810, encoding AP2/B3-domain, was likely to be the candidate gene regulating cucumber cold tolerance. These results provide insight into the genetic basis of cucumber cold tolerance and lay a solid basis for enhancing molecular breeding.