Genetic analysis and QTL mapping of traits related to head shape in cabbage (Brassica oleracea var. capitata L.)

Abstract

Traits related to head shape, including Hvd (head vertical diameter), Htd (head transverse diameter), and Hsi (head shape index, the ratio of Hvd/Htd), are very important agronomic traits associated with both yield and quality in cabbage (Brassica oleracea var. capitata L.). However, reports of inheritance analysis and quantitative trait locus (QTL) mapping of these traits remain rare. In this study, a double haploid (DH) population with 130 lines constructed from a cross between 24-5 (inbred line, oblate head)×01-88 (inbred line, round head) was used to analyze inheritance and to detect QTLs related to Htd and Hsi using major gene plus polygene mixed inheritance analysis and inclusive composite interval mapping (ICIM). The results indicated that Htd was controlled by two independent major genes and polygenes with recessive-epistatic effects. Hsi was controlled by two linkage major genes and polygenes with cumulative effects. A genetic linkage map with 48 insertions or deletions (InDel) and 149 simple sequence repeat (SSR) markers was constructed based on the DH population, with a total length of 866.2cM and an average interval length of 4.40cM. Fourteen QTLs for Htd and Hsi were identified on six chromosomes based on two years of phenotypic data with ICIM. Ten of the QTLs explained greater than 10.0% of the phenotypic variance, and five QTLs could be repeatedly detected in two years. For Htd, two major QTLs, Htd 3.1 and Htd 8.1, explained 19.16–24.56% and 11.25–21.55% of the phenotypic variation in the two years, respectively. For Hsi, two major QTLs, Hsi 7.1 and Hsi 7.2, explained 22.30–24.93% and 14.85–16.79% of phenotypic variation in the two years, respectively. The results from QTL mapping and genetic analysis in both years were partially consistent and complemented each other. Our results provide a foundation for further research on genetic regulation, gene cloning and molecular marker-assisted selection (MAS) for head shape in cabbage.