Identification of quantitative trait loci controlling late bolting in Chinese cabbage (Brassica rapa L.) parental line Nou 6 gou

To identify the genes responsible for varietal differences in bolting time in Brassica rapa, we constructed a linkage map of 220 simple sequence repeat (SSR) markers of B. rapa. To construct the map, we used F2 progeny obtained from a cross between the late-bolting parental line Nou 6 gou (PL6) and the early-bolting parental line Nou 7 gou (A9709). The linkage map covered 875.6 cM and 10 major linkage groups. To investigate the nature of the vernalization response in the B. rapa parental lines, we examined bolting characteristics under two different conditions i.e., greenhouse and open field. Five quantitative trait loci (QTLs) that controlled bolting time were detected by experiments in greenhouse and open field. Interestingly, the QTLs identified in the greenhouse and field experiments did not map to the same loci. Three of five QTLs were colocalized with the orthologs of well-known flowering genes of Arabidopsis, including FLOWERING LOCUS C (FLC) and FLOWERING LOCUS T (FT). The QTLs detected in this study may provide useful information for the selection of bolting traits in Chinese cabbage breeding.