Effects of inhibitors of calcium-dependent metabolism on haustorium formation of Peronospora parasitica in Japanese radish root tissues were investigated. When the root tissues were pretreated with chlortetracycline, EGTA and Na3VO4, respectively, haustorium formation of the fungus was suppressed. The suppression by chlortetracycline was restored by addition of a calcium ionophore or a protein kinase activator. These results suggested that haustorium formation of P. parasitica might be closely related to calcium-dependent metabolic process in host.
Clubroot disease was found on wasabi (Eutrema wasabi Maxim.) growing in drained paddy fields in Yamaguchi Prefecture. The clubroot incidence was high in wasabi plants transplanted from one of two nursery beds set in drained paddy fields, where the occurrence of clubroot on Cardamine flexuosa With., a cruciferous weed, was more frequently observed. In the inoculation test, the clubroot fungus from the weed showed high pathogenicity to wasabi as well as that from Chinese cabbage. It is suggested that the fungus from the weed affects wasabi in fields.