Behavior of DNA Markers Linked to a Clubroot Resistance Gene in Segregating Populations of Chinese Cabbage (Brassica rapa ssp. pekinensis)

Abstract

The usefulness of two restriction fragment length polymorphism (RFLP) markers and one random amplified polymorphic DNA (RAPD) marker linked to a clubroot resistance (CR) gene was investigated in segregating populations of F₂, BC₁S₁ and doubled haploid (DH) generations of Chinese cabbage (Brassica rapa ssp. pekinensis). Discrete segregation for disease ratings, i.e., severe root-galling or no symptoms, was found in the pathogenic fungus-inoculated populations. From the segregation ratios, it is presumed that clubroot resistance was controlled by a single dominant gene, designated CRa. Polymorphisms of the genetic markers were detected in each population. The RFLP marker HC352b and the RAPD marker E49₃₈₀ exhibited dominant segregation, whereas the RFLP marker HC181 segregated co-dominantly. Banding patterns of the DNA markers coincided well with phenotypic segregation for clubroot resistance. The plants with CRa could be selected using an amplified dominant band of E49₃₈₀. Homozygotes for CRa could be selected by detecting a null type for HC352b. A novel CR specific band was detected in the F₂ progeny from a top cross between the CR line T136-8 and the susceptible cultivar ‘Daifuku’. The results of this study indicate that resistant individuals can be efficiently selected using one or more of the polymorphic DNA markers near CRa in segregating populations.