Evaluation of Germplasm and Development of Markers for Resistance to Plasmodiophora brassicae in Radish (Raphanussativus L.)

Abstract

The rapid spread of clubroot disease caused by Plasmodiophora brassicae threatens radish (Raphanus sativus) production in China because some cultivation types lack clubroot-resistant (CR) genes. However, few molecular markers for clubroot resistance have been developed and used in hybrid breeding programs. In this study, 27 immune and 6 highly resistant accessions were identified among 95 radish inbred lines. The genes Rsa10003637 and Rsa10025569/Rsa10025571 were respectively identified from an XYB36-2 reference genome as the homologs of Crr1 and CRa from Brassica rapa by means of homology and synteny analysis. The association between the degree of clubroot resistance and the genotype of these CR genes suggested that Rsa10025569-H3 can be used as a clubroot-resistant haplotype. The sequence identity of Rsa10025569 in clubroot-resistant lines (CR-60 and CR-88) and clubroot-susceptible lines (CR-10 and CR-35) was 92.47%, and there was a 699 bp insertion at the end of the fourth exon in the clubroot-susceptible line. Association analysis of a BC1F1 population derived from the cross CR-88 (resistance) × CR-10 (susceptible) revealed an apparent correlation between polymorphisms at the Rsa10025569 locus and degree of clubroot resistance. On the basis of the results, molecular marker-assisted selection was used to transfer disease resistance genes to susceptible varieties and a new CR germplasm of Xinlimei was obtained.