Control of Plasmodiophora brassicae – literature review and future prospects

Abstract: Plasmodiophora brassicae Woronin (Plasmodiophorida) is the casual agent ofclubroot, the most important soil-borne disease of cruciferous crops worldwide. Losses wereestimated 10-15% of the annual harvest combining all cruciferous crops including importantfood-, industrial- and energy-plants like cole crops, oil seed rape or turnips. The soil-borne andplant-associated nature of plasmodiophorids as well as their obligate biotrophic multi-stage lifecycle with multiple zoosporic, plasmodial, and resting stages has hampered research on thisgroup of pathogens. No efficient control strategies are available so far and resistance of mostcultivars has been proven elusive. Different attempts of biological control including soil-borneand endophytic microorganisms were tested with changing success. A number of potentialbiocontrol agents were successfully tested in green house tests, but in field trials the efficacy ofthese biocontrol agents varied considerably. Soil properties play a key role for the infectionprocess and disease development as well as for the success of biological control. Therefore, untilnow best results to reduce disease symptoms were obtained with integrated pest managementstrategies. One reason why biocontrol agents were not successfully applied until today can be thatthe Plasmodiophorida are taxonomically and ecologically far different from “true fungi” or mostother soilborn pathogens. Recent molecular phylogenies place them in the eukaryotic supergroup“Rhizaria” with a close affiliation to the Cercozoa and Foraminifera. Strategies successful incontrolling fungal diseases cannot necessarily be transferred to organisms of a very differenttaxonomic affiliation. Increased knowledge about the taxonomic position and the biology of thissoil-borne pathogen offers potential targets for the future control of the clubroot pathogen.