An analysis of some effects of light and soil temperature on clubroot disease

In a glasshouse study, 54 batches of cabbage seedlings were each grown for 6 wk in clubroot inoculated soil. The batches were sown at weekly intervals during the experiment which lasted 60 wk. Soil temperature and light were monitored throughout the study while other potential variables were maintained as constant as possible. Records of clubroot incidence, severity and plant weights were kept and causal relationships for disease severity and percentage infected plants sought among the light and temperature data by regressions. It was found that clubroot severity was influenced most by the light level in the second and third weeks, while the percentage of diseased plants was most influenced by temperature, that in the second week probably being the most important. The optimum light value in the second and third weeks for expression of maximum clubroot severity was c. 600 Wh m^-2 day^-1 and a mean daily temperature of not less than c. 19-5 ^oC was required to give close to 100% infection. Possible reasons for the findings are discussed.