Identification and validation of a major QTL controlling the presence/absence of leaf lobes in Brassica rapa L.

Abstract

Leaves are vital plant organs, and a high level of variation in leaf shape, including the leaf lobes, is present in Brassica rapa. Based on a previously-constructed linkage map, QTL analysis of the leaf lobes was performed using the scores from an F2 population during the spring of 2010, and scores from an F2:3 family in the autumn of 2010, respectively. A total of nine QTLs were found to affect leaf lobes. Among these, a major QTL, lob 10.1, was mapped to the bottom of linkage group A10. To develop near iso-genic lines (NILs) for the identified major QTL, an F2 plant without leaf lobes that was homozygous in the targeted region for marker alleles from the male parent (08A061), was backcrossed to 09A001, the recurrent parent with leaf lobes. Two InDel marker loci, BrID10909 and BrID10233, which are closely linked to the major QTL peak position, and 166 SSR and InDel markers from non-targeted chromosomal regions, were used for foreground and background selection, respectively. Three sets of NILs were developed through four cycles of backcrossing followed by two cycles of self-pollination. Compared to 09A001, the recurrent parent, all the NILs showed the absence of leaf lobes and had no significant differences in other agriculturally important traits. NILs are the ideal genetic resource for QTL validation and fine-scale linkage mapping, and, ultimately, gene discovery.