Evaluation of lime products for clubroot (Plasmodiophora brassicae) management in canola (Brassica napus) cropping systems

Clubroot, caused by Plasmodiophora brassicae, is an important soilborne disease of canola (Brassica napus) in Alberta, Canada. As clubroot prefers acidic soils, the application of lime to increase soil pH may reduce disease. Replicated field plot experiments were conducted to evaluate the efficacy of hydrated lime for clubroot management. In 2017, moderate (11.4 t ha(-1)) to high rates (12.7 t ha(-1)) of hydrated lime reduced the index of disease (ID) by 35-91% in a susceptible canola cultivar 8 weeks after seeding. In contrast, no effect of lime treatment was observed in the 2018 field trials, due to several environmental factors. A greenhouse study compared the efficacy of hydrated lime and limestone in reducing ID in susceptible and resistant canola cultivars, at different application rates and inoculum concentrations. In treatments that did not receive lime, ID was very high (92-100%) in the susceptible and low (9-13%) in the resistant canola. The application of hydrated lime at 4.7, 8.1, 11.4 and 14.8 t ha(-1) eliminated visible symptoms in both cultivars, whereas limestone reduced the ID only at the two lowest inoculum concentrations. Root tissues from the same study were analyzed by quantitative PCR to measure P. brassicae proliferation in planta. Inoculum concentration and the type and rate of lime significantly affected the amount of P. brassicae DNA present in the root tissue. Repeated trials with less virulent inoculum indicated similar trends. Hydrated lime may represent a more effective tool than limestone to manage P. brassicae on canola in highly infested soils.

Automated summary

Clubroot, caused by Plasmodiophora brassicae, is a significant soilborne disease in canola crops, and the application of hydrated lime may reduce disease severity. Field experiments showed varying efficacy of hydrated lime in reducing disease index in susceptible canola cultivars, while a greenhouse study indicated its potential effectiveness over limestone in managing the pathogen.