New Clubroot Pathotypes and Second Generation Resistance
Term: 3 years, ending April 2024
Status: Complete
Researcher(s): Stephen Strelkov, Sheau-Fang Hwang, Rudolph Fredua-Agyeman, Keisha Hollman, Emilee Storfie, Victor Manolii, U of A
SaskCanola Investment: $77,625
Total Project Cost: $155,250
Funding Partners: ACPC
Grower Benefits
Mild to severe clubroot could be found in some fields planted with cultivars possessing second-generation resistance.
The performance of the SG cultivars varied widely when inoculated with different P. brassicae isolates under controlled conditions.
The diversity in responses of the SG cultivars to inoculation suggested distinct resistance/combinations of resistance genes in different varieties.
Many isolates showed cross-infectivity, meaning they were recovered from one SG cultivar in the field but were capable of causing clubroot on other SG cultivars in the greenhouse evaluations.
The isolates and pathotypes that were the most virulent on canola with first-generation clubroot resistance were also the most virulent on many of the SG cultivars.
Some SG cultivars exhibited significantly improved resistance to isolates that were virulent on first-generation resistance. In contrast, other SG cultivars had resistance profiles that were either similar or notably inferior.
Second-generation resistance does not always provide improved clubroot protection. Instead, its effectiveness depends on the specific cultivar and pathogen virulence.
Project Summary
Clubroot poses a significant threat to canola growers. Although genetic resistance is critical for managing the disease, changes in pathogen virulence endanger its effectiveness. Second-generation resistance offers promise against pathotypes that can overcome first-generation resistance. However, without an understanding of pathogen virulence on second-generation resistance, we risk compromising its efficacy. This project provided data on the performance of second-generation clubroot-resistant cultivars in the field, along with insights into the virulence characteristics of pathogen populations collected from these cultivars.
Clubroot in canola is primarily managed through the planting of resistant cultivars. Initially, most cultivars shared similar resistance, derived from a European source. However, recent years have seen an increase in pathotypes capable of bypassing this resistance. This has led to the development of new varieties with alternate resistance traits, collectively termed 'second-generation' resistance. This project aimed to: (1) collect clubbed roots from fields with second-generation resistant cultivars, (2) purify pathogen isolates and assess their pathotype designation and virulence on representative cultivars under greenhouse conditions, and (3) use molecular markers to screen isolates to identify distinct pathogen populations.
Annual surveys were conducted to assess the occurrence of clubroot on canola with second-generation resistance. Resting spores were extracted from symptomatic canola roots, with the spores obtained from one plant regarded as one field isolate. Isolates were evaluated for pathotype classification on the Canadian Clubroot Differential set and tested for virulence on seven canola cultivars with second-generation resistance and three control host varieties. Genetic populations of the pathogen were distinguished via quantitative PCR-based assays.
While most of the experiments were conducted under greenhouse and laboratory conditions, the surveys were carried out in the field. Since clubroot severity can vary with local environmental conditions, some symptom-free crops might have developed symptoms under conditions more favorable for the pathogen. However, this consideration does not affect the study’s conclusions.
The effectiveness of second-generation clubroot resistance varied greatly among canola cultivars. Some second-generation cultivars exhibited significantly improved resistance to pathogen isolates that were virulent on first-generation resistance. In contrast, other second-generation cultivars had resistance profiles that were either similar or notably inferior.