Development of Strategies for the Integrated Management of Clubroot of Canola

Abstract

Clubroot, caused by the soilborne pathogen Plasmodiophora brassicae, is a serious disease threatening the production of canola (Brassica napus) in Canada. This project explored various management options for clubroot, including fungicide application, fall and spring liming, and genetic resistance. In the first study, amisulbrom was evaluated for its effectiveness in managing clubroot. In vitro treatment of P. brassicae resting spores with amisulbrom inhibited spore germination by up to 79% and reduced viable spores by 31% relative to the control. Field and greenhouse experiments demonstrated that both liquid and granular formulations of amisulbrom significantly reduced the clubroot disease severity index (DSI) in both susceptible and moderately resistant canola cultivars (‘45H31’ and ‘CS2000’, respectively), relative to the untreated controls. In the second study, fall and spring applications of Zero Grind (ZG) limestone and spring applications of hydrated lime (HL) were assessed for their efficacy in clubroot management on ‘45H31’ in the field, and both ‘45H31’ and ‘CS2000’ in the greenhouse. Both field and greenhouse results showed that the most significant reductions in DSI were obtained with fall ZG and spring HL applications at a rate of 10 t ha-1, regardless of the cultivar, while most lime treatments reduced resting spore load in the field soil. In the third study, an F2 population derived from a B. napus ssp. napobrassica (rutabaga) donor parent FGRA106 and a susceptible spring-type B. napus cv. ‘Sedo’ was evaluated for resistance to P. brassicae pathotypes 3A, 3D and 3H. Chi-square (χ2) goodness of fit tests indicated that the F2 plants inherited two major clubroot resistance genes from FGRA106. Total RNA from plants resistant (R) or susceptible (S) to each pathotype were pooled and subjected to bulked segregant RNA-sequencing (BSR-Seq). Analysis of gene expression profiles identified 431, 67, and 98 differentially expressed genes (DEGs) between the R and S bulks. Collectively, the application of amisulbrom and fall limestone demonstrated promising results for clubroot management. Additionally, the identification of resistance in FGRA106 and its associated genetic markers could contribute to the development of clubroot-resistant B. napus cultivars for deployment in western Canada.