Establishment of an Efficient Screening Methods for Resistance of Chinese Cabbage to Clubroot Disease

Clubroot caused by Plasmodiophora brassicae is an important disease of crucifer crops worldwide. This study aimed to establish an efficient screening method to determine resistant cultivars of Chinese cabbage against P. brassicae. To do this, we investigated the virulence of seven P. brassicae isolates using seedlings of susceptible Chinese cabbage cultivar. The isolates exhibited different virulence in the plants and were divided into three groups based on their virulence. When we explored the disease occurrence in Chinese cabbage seedlings according to photoperiod after inoculation of P. brassicae and incubation temperature, the plants with all-day light showed higher disease severity than seedlings cultivated under 14 hr of light a day. The occurrence of clubroot disease was most severe at 25oC, followed by 20oC and 18oC, but the fresh weight of clubroot of the seedlings cultivated at 20oC was the highest, followed by plants grown at 25oC and 18oC. When the seedlings of two commercial resistant cultivars were inoculated with the mixed spore suspensions of two different pathotype isolates of P. brassicae, disease severity increased as the spore concentration of the susceptible P. brassicae isolate among the two strains increased, suggesting that the clubroot development by different pathotype isolates was independent and not influenced by each other. Taken together, our results provide a faster and more accurate screening methods to determine the resistance of Chinese cabbage against P. brassicae.