Influence of pH, Temperature, and Biofungicides on Clubroot of Canola
Management of clubroot caused by the soil-borne biotrophic plant protist Plasmodiophora brassicae on canola and other Brassica crops is an important challenge to producers. Studies on the interaction of pH and temperature on root hair infection (RHI) and clubroot symptom development in canola roots revealed that high levels of clubroot can occur under optimum temperature, moisture and spore load, even at alkaline pH of 7.5. Clubroot was suppressed at all temperatures at pH 8.0, but not totally eliminated. The occurrence of maximum levels of root hair infection and clubroot development (RHI = 61%, Clubroot incidence (CI) & Disease severity index (DSI) = 100%) at temperatures of 20° and 25°C and pH of 5.0 to 6.5 was confirmed. The efficacy of biofungicides against P. brassicae was influenced by pathogen load, host, growth media and its properties. Drench application of Serenade and Prestop were moderately effective in reducing clubroot levels in canola (Brassica napus L. and B. rapa L.) and to a lesser extent in Shanghai pak choy (B. rapa L. ssp. Chinensis (Rupr.) var. communis Tsen and Lee). The mean clubroot incidence and severity caused by Pathotype 3 was found to be slightly higher than that of Pathotype 6. Clubroot level increased with increase in soil bulk density.