Clubroot remains one of the most challenging diseases in canola production, largely because new pathotypes continue to emerge and weaken the effectiveness of resistance genes.
As research advances and more pathotypes are identified, growers need clear guidance on how resistance is classified, what newer strains mean for hybrid performance, and which management practices offer the best long-term protection.
Understanding these fundamentals helps support informed decisions as clubroot continues to evolve across Western Canada.
Clubroot Pathotypes
Research has identified numerous clubroot pathotypes, including strains capable of overcoming first-generation resistance. The development of the Canadian Clubroot Differential (CCD) set allows pathotypes to be described using:
- A number from the Williams’ Differential set (2, 3, 5, 6, 8)
- A letter (A–Z) from the CCD set
Currently, 43 pathotypes are recognized, and it is estimated that up to 25 can overcome first-generation resistance genes. Several newer pathotypes — such as 3A, 3D, and 8E — are becoming more common in Western Canada. Of these, 3A and 3D are most frequently reported in fields where resistance is breaking down.
Growers in high-pressure areas benefit from using hybrids with next-generation resistance genes supported by sound management practices.
Use of First and Next-Generation Clubroot Resistance
Clubroot-resistant hybrids should be used broadly to help slow spore spread. A minimum two-year break between canola crops reduces inoculum levels and lowers selection pressure on resistance genes.
Scouting is essential when growing first-generation resistant hybrids to detect early signs of resistance breakdown. When resistance-breaking pathotypes are confirmed or suspected in a region, growers should transition to next-generation resistance hybrids after the recommended rotation break.
Clubroot DefendR®
Plant breeders have incorporated multiple resistance sources to create hybrids with broader, more durable resistance. Clubroot DefendR® hybrids contain stacked resistance genes that protect against both older and newer Western Canadian pathotypes, including:
- Established types such as 2F, 3H, 5I, 6M, 8N
- Newer, resistance-breaking types including 3A, 2B, 3D, 8E, 5G, 5K, 3O, 5X
Stacking multiple major resistance genes enhances durability and supports long-term disease management.
Recommended Clubroot Management Practices
The Canola Council of Canada promotes strategies focused on keeping clubroot spores “low and local.”
Practical steps include:
- Using clubroot-resistant hybrids on all canola acres
- Maintaining at least a two-year rotation between canola crops
- Scouting fields regularly to monitor hybrid performance
- Switching to next-generation DefendR® hybrids in areas where resistance breakdown is suspected
Growers outside high-pressure areas can help prolong resistance durability by choosing resistant hybrids such as 6207TF and BY 5125CL, while fields facing resistance challenges should prioritize DefendR® products.
Visit BrettYoung.ca/BY6207TF for further information on performance and its DefendR-rated Clubroot resistance package.
Sources
Source: Canola Council of Canada, 2021.
Concurrent withmmended for areas where the incidence of resistance breakdown is suspected. Visit BrettYoung.ca/BY6207TF for further information on performance and its DefendR-rated, Clubroot resistance package.
1 Strelkov, S.E., Hwang, S.F., Manolii, V.P., Cao, T., Fredua-Agyeman, R.,Harding, M.W., Peng, G., Gossen, B.D., McDonald, M.R., and Feindel, D. 2018. Virulence and pathotype classification of Plasmodiophora brassicaepopulations collected from clubroot resistant canola (Brassica napus)inCanada. Can. J. Plant Pathol. 40:284-298. DOI:10.1080/07060661.2018.1459851
2 Askarian, H., Akhavan, A., Manolii, V.P., Cao, T., Hwang, S.F., and Strelkov, S.E. 2020. Virulence spectrum of single-spore and field isolates of Plasmodiophora brassicae able to overcome resistance in Canola (Brassica napus). Plant Disease, 105:43-52, DOI:10.1094/PDIS-03-20-0471-RE
3 Hollman, K.B., Hwang, S.F., Manolii, V.P., and Strelkov S.E. 2021. Pathotypes of Plasmodiophora brassicae collected from clubroot resistant canola (Brassica napus L.) cultivars in Western Canada in 2017-2018. Canadian Journal of Plant Pathology, DOI: 10.1080/07060661.2020.1851893
FAQ
What is clubroot and why is it a threat to canola production?
Clubroot is a significant disease that threatens canola production mainly because emerging pathotypes can overcome the resistance in current canola hybrids, making management and prevention more difficult.
How are clubroot pathotypes identified?
Clubroot pathotypes are identified using a combination of a number from the Williams’ Differential set and a letter from the Canadian Clubroot Differential (CCD) set such as 3A or 8E.
What steps should growers take to manage clubroot resistance in canola crops?
Growers are advised to deploy clubroot-resistant hybrids on all acres and use a crop rotation with at least a two-year break between canola crops. Active scouting for disease helps monitor performance and detect resistance-breaking pathotypes early.
What is the DefendR Clubroot trait and how does it help manage clubroot?
The DefendR Clubroot trait involves stacking multiple clubroot resistance genes into single hybrids which offers resistance to both older and newer clubroot pathotypes, making resistance more broad and durable in next-generation hybrids.
