9:00 am - 10:00 am
A graduate exam seminar is a presentation of the student’s final research project for their degree.
This is an ALES MSc Final Exam Seminar by Brittany Hennig. This seminar is open to the general public to attend.
Thesis Topic: Evaluation of Resistance, Hydrated Lime, and Weed Control to Manage Clubroot in Canola
MSc with Drs. Stephen Strelkov and Sheau-Fang Hwang.
Plasmodiophora brassicae Wor. is a soilborne parasite causing clubroot of canola (Brassica napus L.), a serious disease managed mostly by planting clubroot resistant (CR) cultivars. Recently, new pathotypes of P. brassicae have emerged that overcome resistance, highlighting the need for a greater understanding of resistance stewardship and an integrated approach to clubroot management. Replicated field experiments were conducted in Edmonton, AB, in 2018 and 2019, to evaluate the effect of lime application and weed management on clubroot severity, crop yield and various growth parameters in clubroot susceptible (CS) and CR canola cultivars. P. brassicae resting spore densities were also monitored by quantitative PCR for each treatment. When hydrated lime was applied to increase the soil pH from initial values of 5.2-5.5 to 7.2, clubroot severity decreased by 34-36% in the CS canola cultivar, while seed yield increased by 70-98%. On CR canola, clubroot severity was reduced by an average of 9% but yield was not significantly affected. The application of hydrated lime also decreased resting spore densities by 48-80%, relative to untreated controls, in plots where the CS cultivar was grown, while the lime application or management of weeds did not significantly affect spore densities in plots with the CR cultivar. While the management of weeds did increase seed yield by an average of 35% in the CR canola and 21-40% in the CS canola, this likely reflected reduced competition rather than a direct effect on P. brassicae spore levels or clubroot severity. The field trials were complemented by a greenhouse experiment in which CS and CR canola cultivars were grown in different combinations (CR/CR, CR/CS, CS/CR, CS/CS) in a canola-wheat-barley-canola rotation with different initial spore densities of P. brassicae (0, 1 x 102, 1 x 104, 1 x 106, 1 x 108 spores per g soil mix). Clubroot severity increased in CR canola when it was grown twice in the rotation, but only when the initial spore concentrations were 1 x 106 or 1 x 108 spores/g soil mix. The results from the field trial suggest that the application of hydrated lime may be a useful strategy to manage clubroot, when used in combination with genetic resistance to reduce disease pressure. The greenhouse experiment suggested that there is a reduced risk of resistance erosion when a CR cultivar is deployed in mildly infested soils with a 2-year break, but this must be confirmed under field conditions. Ultimately, a combination of strategies will be required for sustainable clubroot management.