Germplasm screening and inheritance analysis of resistance to cabbage black rot in a worldwide collection of cabbage (Brassica oleracea var. capitata) resources

Abstracts Xanthomonas campestris pv. campestris (Xcc) is the causal agent of cabbage (Brassica oleracea var. capitata) black rot (BR) that leads to severe yield losses worldwide. Cultivation and application of resistant cultivars is the most desirable way to control BR. However, due to the lack of BR-resistant germplasm resources and an unclear understanding of the resistance inheritance as well as the controlling gene, the breeding process has been seriously hindered. To identify new BR resistance sources to Xcc race 1, 162 cabbage accessions collected worldwide were evaluated using the spray inoculation method. In total, 64.2% of them were susceptible, and only four germplasms were highly resistant, including two inbred lines (‘05-574-323’ and ‘MD219’) and two hybrids (‘Qinglian’ and ‘Dadilv 2’). Further, to define the genetic characteristics of resistance, a mixed major gene plus polygene inheritance model was used to analyze BR resistance in six populations (P1, P2, F1, B1, B2, and F2) derived from the resistant parent ‘05-574-323’ and the susceptible parent ‘02-359’. The results showed that BR resistance was controlled by a pair of additive major genes and additive-dominant multiple genes (D-2 model), and the main gene heritabilities of B1, B2, and F2 were 49.29%, 43.53%, and 50.35%, respectively. The resistant accessions obtained in this study provide new resources for cabbage BR-resistance breeding, and the inheritance analysis opens the gate for further mapping and application of the resistance gene.