Effects of growing leafy daikon (Raphanus sativus) on populations of Plasmodiophora brassicae (clubroot)

Control of some soilborne pathogens may be achieved by use of decoy or catc h crops. These stimulate the germination of resting spores, resulting in li mited expression of disease symptoms. Results achieved using this approach are reported here using leafy daikon (radish, Raphanus sativus var. longipi nnatus) for control of Plasmodiophora brassicae, the cause of clubroot dise ase of Brassicaceae. Disease indices of Chinese cabbage plants grown in pot s that had previously contained leafy daikon were lower compared with pots where no plants had been grown before (control pots). Numbers of resting sp ores of P. brassicae in soil in pots after cultivation with leafy daikon we re reduced by 71% compared with control pots when resting spores were recov ered and counted directly. In a field experiment, numbers of resting spores were reduced by 94% compared with the start of the experiment when leafy d aikon was grown in advance of Chinese cabbage, but there was no reduction i n disease severity in the Chinese cabbage. Plasmodiophora brassicae infecte d the root hairs of leafy daikon and those of Chinese cabbage, but no clubs were found on leafy daikon roots. The results from pot trials indicate tha t leafy daikon may be useful as a decoy crop for the control of clubroot di sease in field crops.