Clubroot is a costly canola disease that growers need to be aware of and understand the recommended management practices for. The latest research confirms the continued spread of the disease throughout the canola-growing areas of Canada. Many new pathotypes are present in the intensive clubroot areas of Alberta, where the disease was first identified in Western Canada; however, new pathotypes are being identified in other canola-producing regions. This is a result of too often relying on the protection provided by a hybrid’s genetic resistance and ignoring the need for an integrated pest management approach with a diverse crop rotation. It’s well documented in clubroot areas that intensive canola rotations are a serious factor in aggravating disease incidence and are creating conditions for new clubroot pathotypes to emerge. These new emerging pathotypes are spreading at a slower rate but still pose a challenge for plant breeders to develop hybrids that provide effective protection against them.
The discovery of new pathotypes capable of overcoming first-generation clubroot-resistant hybrids has generated a significant amount of research to characterize these pathotypes and identify new sources of genetic resistance. One result of this research is the development of the Canadian Clubroot Differential (CCD) set. Pathotype identification is based on the combination of a number (2, 3, 5, 6, 8) from the Williams’ Differential set with a letter (A through Z) from the CCD set1. Identification of new pathotypes continues, and it is believed that of the 43 pathotypes currently recognized, as many as 25 can overcome first-generation resistance genes2,3
Certain newer pathotypes such as 3A, 3D and 8E are overcoming the first-generation resistance genes found in many canola hybrids. The 3A and 3D pathotypes are the most frequently reported clubroot pathotypes where canola hybrids are showing susceptibility. Adopting hybrids with next-generation clubroot resistance genes and adopting appropriate management practices will be key for growers in areas where the risk of new clubroot pathotype emergence is high.
Use of First and Next-Generation Clubroot Resistance
Clubroot-resistant hybrids should be deployed broadly on all acres. A crop rotation with at least a two-year break between canola crops will alleviate clubroot spore levels and minimize selection pressure. Growing first-generation resistant hybrids is to be followed up with active disease scouting to monitor hybrid performance and help to identify resistance-breaking pathotypes early. If there are known resistance overcoming pathotypes in the region, growing a next-generation clubroot-resistant hybrid is recommended after a two-year break from canola.
BrettYoung’s Clubroot DefendR: Broad Resistance with a Multi-genic Approach
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 clubroot in hybrids with the DefendR Clubroot trait. This trait has resistance to the older pathotypes that were first identified in Western Canada (2F, 3H, 5I, 6M and 8N) and to many newer pathotypes, including 3A, 2B, 3D, 8E, 5G, 5K, 3O and 5X. Stacking major clubroot resistance genes into single hybrids is an important factor on how effective and durable the resistance will be in next-generation clubroot resistance products.
Recommended Clubroot Management Practices
The Canola Council of Canada (CCC) provides a list of recommendations to manage the spread of clubroot spores by focusing on keeping them low and local.
Source: Canola Council of Canada, 2021.
Growers in areas not impacted by first-generation resistance overcoming pathotypes can prevent the accumulation of spores for as long as possible by using resistant hybrids such as 6207TF and BY 5125CL. Hybrids with the DefendR clubroot trait are recommended 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.