Surface Disinfestation of Resting Spores of Plasmodiophora brassicae Used to Infect Hairy Roots of Brassica spp.

ABSTRACT Resting spores of Plasmodiophora brassicae were surface-disinfested by treatment with 2% chloramine-T for 20 min and then with an antibiotic solution (1,000 ppm of colistin sulfate, 1,000 ppm of vancomycin hydrochloride, and 6,000 ppm of cefotaxime sodium) for 1 day. The disinfested resting spores were used to inoculate hairy roots of cabbage (Brassica oleracea var. capitata cv. Fuji Wase), Chinese cabbage (B. pekinensis cv. Musou Hakusai), turnip (B. rapa var. rapifera cv. Wase Okabu), and rape (B. napus line Dc 119). Differences among hosts in susceptibility to clubroot in hairy roots were evident. Chinese cabbage and turnip hairy roots supported the highest percentages of root hair infection (53.3 to 80%) and the greatest production of zoosporangial groups (8.5 to 32.5 per root). Moreover, gall formation was observed only on Chinese cabbage and turnip hairy roots. The morphology of zoo-sporangia, plasmodia, and resting spores in diseased hairy roots was found to be identical to that in infected intact plants by both light and scanning electron microscopy. Pathogenicity tests confirmed the infectivity of resting spores produced in hairy roots. Thus, the hairy root culture technique should prove useful as a dual culture system for P. brassicae.