QTL mapping and epistasis analysis for plant height and height to the first branch in rapeseed ( Brassica napus L . )

Since plant height and height to 1-st branch are complicated quantitative traits. QTL analysis can help us to understand the basis of heterosis and improve the selecting efficiency. A genetic linkage map consisting of 244 molecular markers was constructed based on F2 population derived from a cross between double low CMS maintainer 1141B and double high restorer KenC1. The markers in the linkage map distributed on all the 20 main linkage groups and 1 triplet and covered 2769.5 cM of the rapeseed genome. The statistic software of Windows QTL Cartographer Version2.0 and Composite Internal Mapping (CIM) were applied to detect QTLs for plant height and height to 1-st branch. A total of 7 QTLs located in 5 different linkage groups were identified for these two traits. The QTLs explained the phenotypic variation from 8.54% to 54.59% individually , and all of them showed that 1141B decreased the plant height and the height to 1-st branch. Furthermore, fifteen two-locus combinations showed significant epistatic effects, which separated in the entire genome for both traits. The epistatic interactions had pleiotropic effects between two traits. Interactions were detected between QTL and non-QTL (non-significant effect loci) and between two non-QTLs. The later was the majority. AA was the most common type of interactions in plant height. DD and DA were the most common type of interactions for height to 1-st branch. This indicated that the genes controlling plant height and height to 1-st branch were complicated. Epistasis interactions might play an important role. Some questions were also discussed.