Against clubroot, ‘I’-rated canola sits between ‘R’ and ‘S’

A new canola variety billed with “intermediate” reaction against a new pathotype of clubroot is being placed in the zone between “resistant” and “susceptible.”

Canterra Seeds, the Winnipeg firm marketing the new CS2000 hybrid variety, clarified its claim for the seed in a statement on a company blog Wednesday, granting many growers may be seeing the term “intermediate reaction” for the first time.

Canterra launched the variety last month as a Genuity Roundup Ready hybrid suitable for all growing zones, with “R” (resistant) ratings for blackleg as well as for clubroot pathotypes 2, 3, 5, 6 and 8.

It also touted the new variety as the only hybrid on the market to have shown tolerance to clubroot pathotype 5x. The new pathotype was discovered in some canola fields in the Edmonton area in 2012 after plants from other R-rated varieties reacted to it.

The Alberta Canola Producers Commission on Monday had sought clarification on the term “intermediate” as it’s been applied to CS2000.

“While there is an agreed definition of what an intermediate reaction to the pathogen is, there is no general agreement about what an intermediate level of resistance means for yield loss or managing the buildup of resting spores in the soil,” commission general manager Ward Toma said in a release.

In its response Wednesday, Canterra cited both University of Alberta plant pathologist Stephen Strelkov and the pathology sub-committee of the Western Canadian Canola/Rapeseed Recommending Committee (WCC/RCC).

According to Canterra, both define “intermediate reaction” as a level of reaction to disease between 30 and 69 per cent.

By comparison, plants of an R-rated canola variety show 30 per cent or less reaction to a disease compared to a highly susceptible variety — and a variety from which the plants show 70 per cent or more reaction is rated susceptible (“S”).

When ranking canolas for their resistance to blackleg, the WCC/RCC further breaks down the zone between “R” and “S” into “moderately resistant (MR),” showing a blackleg severity level of 30-49 per cent compared to a highly susceptible variety, and “moderately susceptible (MS),” showing a severity level of 50-69 per cent.

Canterra emphasized in its blog post that a variety with an intermediate reaction against clubroot 5x is “not a silver bullet” against the pathotype.

Both the company and ACPC urged growers to continue to use all best-management practices for clubroot, such as cleaning equipment and rotating crops in affected fields, as well as choosing resistant varieties.

ACPC’s Toma said Monday it’s encouraging that some varieties aren’t “completely susceptible” to 5x.

“Up to this point, everything that was exposed to (5x) died, so this result offers evidence that strong resistance (against 5x) may yet be found.” — AGCanada.com Network