Studies of components for a potential integrated control system for Plasmodiophora brassicae
The soil inhabiting organism Plasmodiophora brassicae infects brassica crops causing millions of pounds of damage each year. The result of infection is extensive galling of the root system and eventually plant death. Current control measures are limited and the variability of the pathogen and its lifecycle makes finding new controls difficult. It was therefore considered that if several measures could be identified which reduced P. brassicae infection then they could be used in combination, reducing the possibility that the pathogen could evolve to overcome the controls. This research therefore aimed to find a set of control measures, and where possible a mode of action, which could be used in combination or alone to reduce P. brassicae infections. Calcium nitrate was identified as an effective control measure which affected several stages of P. brassicaes lifecycle (Fig :1) as well as the predominant pathogen race. The type of growth medium used was also found to affect the extent of infection and to influence the pathogen population. Soils from two areas were identified as suppressive to P. brassicae and the nature of their suppression was determined to be due to both biotic and abiotic factors. The identification of these suppressive soils may lead to the development of a bio-control or it may be possible to encourage these soils to develop in other areas. Some more "holistic" control measures were also investigated. Applications of calcified seaweed were found to be at least as effective in decreasing clubbing as calcium carbonate. Applications of chitin and seaweed extract however were found to have no effect on P. brassicae infection in this instance. The research within this thesis has identified several control measures and answered some questions about P. brassicae. It has however, also raised more questions and identified areas which require more research.