QTL mapping of low temperature germination ability in cucumber

Cucumber is of tropical origin and is sensitive to low temperature. In temperate growing regions or production areas at a high altitude, low temperature germination (LTG) ability is an ideal trait that would allow for early planting. However, the genetic basis for LTG ability in cucumber is poorly understood. In the present study, we conducted QTL analysis for LTG ability using a recombinant inbred line (RIL) population derived from the cross between the LTG tolerant variety Coolgreen and the sensitive inbred line 7088D. Phenotypic data on LTG ability in terms of germinate rate at 13 degrees C were collected from 138 RILs in five environments which were used in QTL analysis. Three QTL, qLTG1.2, qLTG2.1 and qLTG4.1 on chromosomes 1, 2 and 4, respectively, were consistently detected across multiple environments, which could explain 27.3-52.5% observed total phenotypic variance. The two QTL qLTG1.2 and qLTG2.1 exhibited major- and minor- positive effects on increasing LTG ability, respectively, whereas qLTG4.1 had moderate but negative effect on LTG in this RIL population. Additional QTL analysis using 67 recombinant F-2:3 families identified from 602 7088DxCoolgreen F-2 plants validated the major-effect QTL qLTG1.2, which also allowed to narrow this QTL down to a region of348kb in size. Results from this study provide a basis for further fine mapping and functional study of QTL for low temperature germination in cucumber. The knowledge is also useful for marker-assisted selection in breeding for this trait.