Canada
December 23, 2010
Clubroot remains a serious threat to the long-term viability of canola in Western Canada, even though some Alberta counties are relaxing or eliminating crop rotation rules for fields with the disease. Some counties have chosen to replace rotation controls with a clubroot code of practice that puts the rotation decision back into the hands of growers — who now have clubroot-resistant varieties as a key management tool.
While clubroot resistance is a valuable way to reduce disease severity in clubroot-infested fields, crop rotation and other management measures are still important. Growers can’t let their guard down.
“Tight rotations with canola every two or three years will threaten the long-term viability of the clubroot resistance trait,” says Clint Jurke, agronomy specialist with the Canola Council of Canada. “Clubroot remains a very serious disease. Tight rotations that allow clubroot to continue to spread, increase in severity, and adapt to genetic resistance threaten the ability to produce viable canola crops on those and surrounding fields. This could in turn threaten the entire canola industry.”
Clubroot resistance likely comes from a single gene, and based on experience in other clubroot regions, single gene resistance does not seem durable. The pathogen adapts quickly. A winter canola variety called Mendel was released in the U.K. in 2003 and by 2007 resistance was failing. Australia has reported widespread failure of clubroot-resistant Chinese cabbage, a brassica relative to canola. And in North America in the 1960s, a clubroot-resistant cabbage variety called Bagger Shipper lost its resistance fairly quickly with tight rotations.
Bagger Shipper’s resistance trait could be somewhat restored if the variety was not grown for three or more years, which demonstrates the potential value of variety rotation. But that also means the pathogen population can shift quickly, adapting to single-gene resistance. Researchers are working to determine the genetic diversity of clubroot in Alberta. The more pathogen races found, the less durable single-gene resistance tends to be.
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