ABSTRACT
Although clubroot (caused by Plasmodiophora brassicae) is one of the most damaging diseases afflicting cauliflower crops, not much is known about its actual extent and the interaction between parasite and soil factors. This paper starts by giving the findings of a study to estimate soil infectivity and discover the extent and distribution of the disease on a 100 hectare vegetable growing area divided into 160 parcels. According to the study, 40% of the parcels are infected with the disease to varying degrees. By comparing the clubroot receptiveness of 14 different soils, it was shown that future infection risks for uncontaminated soils differ greatly. In general terms, soils are at greater risk the more acidic they are, but pH levels alone do not explain every case. It seems, in particular, that autoclaving increases receptiveness to different extents, depending on soil type. The cumulative effect of the two associated treatments (acidification + autoclaving) indicates that a specific type of microflora might influence the parasite’s life cycle, thus encouraging development of the disease in an acidic environment.
