Survival and extinction of Xanthomonas campestris pv. campestris in soil

Carry-over of inoculum of X.c. pv. campestris in the soil from one cropping season to the next was studied in field experiments over three years. Thes e studies were supported by laboratory and greenhouse experiments on quanti tative assessment of bacteria by bioassay using the Most Probable Number te chnique, and on recovery rates of bacteria from the soil. The mean recovery rate from artificially infested soil was 58%. Extinction of X.c. pv. campe stris in soil infested with infected plant debris proceeded exponentially a nd extinction rates depended on temperature, as did the decomposition of pl ant debris. In replicated field plots, over three years, infection foci of black rot disease were established. At harvest time, all plants were choppe d and resulting plant debris was rotovated into the soil. The resulting soi l infestation was sampled and showed clear infestation foci reflecting the original infection foci of the crop. These infestation foci decreased with time and disappeared after the winter. Follow-up crops remained virtually u ninfected. The results show that in The Netherlands good crop and soil mana gement impedes survival of inoculum from one year to the next, so that cabb age can be grown continuously. Polyetic carryover of inoculum by debris in the soil can be avoided in The Netherlands.