Clubroot: pathotype update, genetic resistance
Date & Time
Tuesday, January 9, 2024, 9:30 AM - 10:00 AM
Keisha Hollman

Clubroot, caused by the pathogen Plasmodiophora brassicae, continues to pose a significant threat to canola production on the Prairies. Testing of symptomatic root samples collected from Alberta in 2019 and 2020 indicated the presence of 25 unique pathotypes, including 15 pathotypes able to overcome ‘first-generation’ or Mendel-derived resistance found in many canola cultivars.  Due to the increasing prevalence of these resistance-breaking pathotypes of P. brassicae, numerous cultivars have been released that carry ‘second-generation’ resistance. While the basis of this resistance is not in the public domain, it is believed to be distinct from or in addition to first-generation resistance. Isolates of the clubroot pathogen collected in 2019, 2020, and 2021 from fields sown to canola with second-generation resistance were assessed for their virulence under greenhouse conditions on a suite of seven cultivars carrying second-generation resistance.  Most cultivars developed moderate to high clubroot severity following inoculation, although at least one cultivar showed strong resistance against all of the isolates tested.  These results suggest that P. brassicae populations continue to adapt to host selection pressure, and that proper resistance stewardship, combined with other management strategies, will be required for long-term clubroot control.