2021 Clubroot Update

Clubroot (CR) continues to be a costly disease for canola growers across Western Canada, and ongoing research shows it is spreading through Alberta, Manitoba, Saskatchewan, and North Dakota. As new pathotypes are identified and resistance pressure increases, understanding how the disease behaves and how resistance is holding up remains essential for effective management. 

Clubroot Spread and Emerging Pathotypes 

Clubroot has continued to move through traditional hotspots as well as newer regions. Many of the newest pathotypes have been identified in intensive CR areas of Alberta — where the disease was first detected in Western Canada — but additional new types are now present in Manitoba and North Dakota as well. 

Surveys in these areas often show high levels of CR incidence even in hybrids that carry first-generation resistance genes, suggesting that resistance alone is no longer enough when rotations are too short. Frequent reliance on genetic resistance, without sufficient time between canola crops, has contributed to resistance breakdown. 

Short rotations have already been clearly linked to increased disease incidence in intensive CR regions, creating ideal conditions for new pathotypes to emerge. Once established, these pathotypes can rise quickly to levels that cause serious concern because most existing commercial hybrids do not protect against them. 

Two key themes are emerging for growers, agronomists, and breeders: 

• CR risk is expanding: The disease is becoming a concern for most canola-growing regions in Western Canada and North Dakota, making hybrid resistance profiles increasingly important in variety selection. 
• Integrated approaches are essential: Growers in high-pressure areas are more likely to encounter new pathotypes that overcome first-generation resistance, reinforcing the need for longer rotations and diversified resistance sources. 

Pathotypes Capable of Overcoming First-Generation Resistance 

Certain newer pathotypes such as 3A, 3D and 8E are reportedly overcoming the first-generation resistance genes found in many commercial varieties. 

The 3A and 3D pathotypes, however, are by far the most frequently reported CR pathotypes where canola varieties are showing susceptibility. Thus far, these new pathotypes are primarily a concern only for growers around Edmonton, Alberta and isolated areas of south-central Manitoba and north-central North Dakota. 

Adopting varieties with next-generation CR resistance genetics and adopting appropriate cultural practices will be key for growers in areas where risk of new CR pathotype emergence is high. 

The Emerging Picture of Pathotype Diversity 

While Northern Alberta’s overall incidence rate of CR infestation is well ahead of other canola producing areas, recent CR surveys suggest that the two regions mentioned previously are also seeing a much higher level of pathotype diversity than the Edmonton area. 

South-central Manitoba and north-central North Dakota are creating a far more complex situation for breeders who are working to screen and characterize new sources of CR resistance genes in their efforts to stay one step ahead. 

The stacking of major CR resistance genes into single varieties appears to be an important factor in how effective and durable the resistance will be in next-generation CR resistant hybrids. 

First vs. Next Generation 

First-Generation Clubroot-Resistant Varieties 

First-generation clubroot-resistant varieties tend to be varieties that can trace their resistance genetics to a resistance profile similar to the European-bred winter canola variety “Mendel”. 

These varieties are typically resistant to pathotypes 2, 3, 5, 6 and 8 (per the Williams’ Differential set, which are equivalent to pathotypes 2F, 3H, 5I, 6M and 8N on the CCD set). 

Next-Generation Clubroot-Resistant Varieties 

There is no standard industry definition but in general, next-generation Clubroot-resistant varieties include first-generation resistance genes but should also contain additional resistance genes that may provide protection against newer pathotypes such as 3A, 2B, 3D, 8E, 5G, 5K, 3O and 5X. 

Consult the supplier of the variety for specific resistance profile information. 

BrettYoung’s Clubroot DefendR®: Broad Resistance with a Multi-genic Approach 

With the presence of new Clubroot (CR) pathotypes being found across the Western Canadian and Northern US prairies that can overcome first generation CR resistance it’s important to be aware of the ways to combat the evolving disease. 

Concurrent with the identification of new pathotypes, breeders have been identifying and incorporating new sources of resistance into the latest canola hybrids. This includes the stacking of multiple sources of resistance to CR in varieties like 6076 CR. 

This variety has resistance to the older pathotypes that were first identified on the Prairies (2F, 3H, 5I, 6M and 8N) and also to many newer pathotypes, including: 

• 3A resistance: Protects against the 3A pathotype now occurring in certain regions.   
• 2B resistance: Offers protection additional to that found in first-generation varieties.   
• 3D resistance: Targets a newer, problematic pathotype emerging in some high-risk areas.   
• 8E resistance: Extends durability to lessen risk of resistance breakdown.   
• 5G resistance: Provides another layer for evolving strains.   
• 5K resistance: Extra source of defense for expanding pathotype diversity.   
• 3O resistance: Increases the spectrum of resistance.   
• 5X resistance: Guards against some of the newest identified types.   

If you live in an area where CR is a concern, there are some best management practices you can follow in order to reduce your risk of infection and yield loss. 

Recommended CR Management Practices 

• Extend crop rotations: Reduce spore load in soil by lengthening the time between canola crops.   
• Use resistant hybrids proactively: In higher risk areas, use first-generation resistant hybrids prior to infestation to delay the accumulation of CR spore loads that cause symptoms.   
• Utilize next-generation hybrids with rotation: Use next-generation resistant hybrids with a minimum of three-year rotation in fields with high levels of infestation.   
• Scout and monitor fields: Regularly check fields to detect the presence of disease symptoms early.   
• Conduct soil testing: Test for the presence of pathogen spores in soil samples.   
• Sanitize equipment: Properly clean machinery to avoid moving infected soil between fields.   
• Control volunteers/weeds: Manage canola volunteers and weeds that act as CR host plants.   

Growers in Manitoba, Saskatchewan and other areas not impacted by pathotype 3A can prevent the accumulation of spores for as long as possible by using resistant varieties such as 6090 RR, BY 6204TF and BY 5125CL. 

BY 6207TF and BY 6076 CR are recommended for areas where incidence of resistance breakdown is suspected. 

Learn more about BrettYoung Clubroot resistant varieties by contacting your Regional Account Manager. 

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