The Impact of Clubroot Resistant Canola Cultivars on Plasmodiophora brassicae Resting Spore Concentrations in the Soil

  • Author / Creator
    Ernst, Thomas W
  • The soilborne pathogen Plasmodiophora brassicae Woronin, causal agent of clubroot of canola (Brassica napus L.), is difficult to manage due to the longevity of its resting spores, its ability to produce large amounts of inoculum, and the prohibitive costs of effective fungicides. The cropping of clubroot resistant (CR) canola cultivars is one of the few effective strategies for clubroot management. This study evaluated the impact of CR canola cultivars on P. brassicae resting spore concentrations in commercial cropping systems in Alberta, Canada. Soil was sampled pre-seeding and post-harvest at multiple geo-referenced locations within 17 P. brassicae-infested fields over periods of up to four years in length. Resting spore concentrations were measured by quantitative PCR analysis, with a subset of samples also evaluated in greenhouse bioassays with a susceptible host. The cultivation of CR canola in soil with quantifiable levels of P. brassicae DNA resulted in increased inoculum loads. There was a notable lag in the release of inoculum after harvest, and quantifiable P. brassicae inoculum peaked in the spring following years when resistant canola was cultivated. Rotations that included a ≥2-year break from P. brassicae hosts resulted in significant declines in soil resting spore concentrations. A strong positive relationship was found between the bioassays and qPCR-based estimates of soil infestation. The results suggest that CR canola should not be used as a tool to reduce soil inoculum loads, and that crop rotations in P. brassicae infested fields should include breaks of at least two years away from B. napus.

  • Subjects / Keywords
  • Graduation date
    Fall 2016
  • Type of Item
  • Degree
    Master of Science
  • DOI
  • License
    This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.