Fine Mapping of Clubroot Resistance Loci CRA8.1 and Candidate Gene Analysis in Chinese Cabbage (Brassica rapa L.)

Abstract

Clubroot is caused by <i>Plasmodiophora brassicae</i>, which threatens <i>Brassicaceae</i> crop production worldwide. In recent years, there has been an outbreak and rapid spread of clubroot in many major cruciferous crop-producing areas of China. In this study, we identified a cabbage material DingWen (DW) with different resistant capabilities from Huashuang5R (H5R) and Huayouza62R of <i>Brassica napus</i>, which are currently used as the main resistant cultivars for clubroot management in China. We used a next-generation sequencing-based bulked segregant analysis approach, combined with genetic mapping to identify clubroot-resistant (CR) genes from F₁ population generated from a cross between the DW (CR) and HZSX (clubroot susceptible). The CR locus of DW (named <i>CRA8.1</i>) was mapped to a region between markers A08-4346 and A08-4853, which contains two different loci <i>CRA8.1a</i> and <i>CRA8.1b</i> after fine mapping. The <i>CRA8.1b</i> loci contain a fragment of 395 kb between markers A08-4624 and A08-4853 on A08 chromosome, and it is responsible for the resistance to <i>PbZj</i> and <i>PbXm</i> isolates. However, together with <i>CRA8.1a</i>, corresponding to a 765-kb region between markers A08-4346 and A08-4624, then it can confer resistance to <i>PbXm</i> ⁺. Finally, through expression analysis between resistant and susceptible materials, two genes encoding TIR-NBS-LRR proteins (<i>BraA08g039211E</i> and <i>BraA08g039212E</i>) and one gene encoding an RLP protein (<i>BraA08g039193E</i>) were identified to be the most likely CR candidates for the peculiar resistance in DW.