A High Density Linkage Map Facilitates QTL Mapping of Flowering Time in Brassica rapa

Flowering is a major developmental transition in the life-history of plants. Flowering time is under complex genetic control. In this study, 172 doubled haploid (DH) lines derived from a cross between two Chinese cabbage (Brassica rapa ssp. pekinensis) DH lines, Y177 and Y195, were used for a high density linkage map construction and quantitative trait locus (QTL) mapping for flowering time in B. rapa. Parents and DH lines were resequenced at depth of 5× and 0.5× coverage, respectively. In total, 22 747 SNPs were called from the resequencing data and combined into 1 708 bins to construct the genetic linkage map. The map length was 958.6 cM, containing 887 bins and the average interval between bin-markers was 1.08 cM. A total of six QTLs controlling flowering time were detected under four different conditions. Potential candidate flowering homologues located near QTLs were identified with the aid of B. rapa genome annotation.