Genetic analysis and mapping of QTLs for isolated microspore embryogenesis in cabbage

Cabbage (Brassica oleracea var. capitata) is an important vegetable cultivated globally. Traditional breeding of cabbage commercial hybrids usually costs 7-8 years for the production of homozygous parental lines. Microspore culture is an effective technique to produce homozygous doubled haploid (DH) lines in only two years, which significantly accelerates the cabbage breeding process. However, the genetic loci associated with the embryogenesis of cabbage microspores have not been studied, which limits the further application of the technique. In this study, 109 DH lines, derived from a cross of the highly embryogenic genotype 01-88 and the nonembryogenic genotype 02-12, were used for QTL mapping of embryogenesis. Genetic analysis indicated that the embryogenesis in cabbage was a quantitative trait controlled by multiple genes. QTL-seq showed that a QTL locus controlling cabbage embryogenesis ability was mapped to an interval of 57.4-58.4 Mb on chromosome C03. An interval of 54.13-57.76 Mb on chromosome C03 was further identified through the genetic map and the traditional genetic linkage analysis to verify the accuracy of QTL-seq. The LOD value of this interval was 2.53-3.6, which could explain the highest phenotypic variation rate of 14.6%. In addition, 12 genes with nonsynonymous mutations were identified in the candidate interval. The gene homologous to DEFECTIVE KERNEL1 (DEK1) was identified as an important candidate gene, which has a large degree of variation between 01-88 and 02-12. The results of this study will lay the foundation for the cloning of genes controlling the embryogenesis of cabbage microspores and the large-scale application of microspore culture technology in cabbage breeding.