If seeding early is the Robertson screw driver of the disease management tool box, genetic resistance is the giant sledge hammer — effective, reliable, easy to use. But unlike actual tools that do the same job over and over again, genetic resistance — that is, resistance to a disease or pest that’s built in to the plant’s own genes — is far more complex.
Earlier this week, the Canola Council of Canada alerted farmers that existing genetic resistance to clubroot was already showing signs of losing its effectiveness. Yes, already. The increasing incidence of blackleg, and the confirmation in recent years of new races of the disease are also of a concern. To shift the focus to cereals, resistance to certain strains of rust have already come and gone.
What’s happening here? Are these varieties just no good anymore? First, let’s clarify something — the clubroot resistant varieties we have and that are being grown are solid lines. There’s nothing wrong with these varieties, in fact, the seed companies should be acknowledged for how quickly they brought the trait to market. What we’re seeing now is an intersect between the type of resistance the varieties’ have (whether it is single vs. multi-gene), the disease pressure and the selection pressure, i.e. how many times in a row canola, and the same variety of canola, has been grown on the same field.
In short, genetic resistance is, yes, the gold standard in disease management, but agronomists and farmers must strive to fully understand how it works and, more importantly, that any and all resistance requires management. This is not simply a clubroot issue. This is not only a blackleg issue. It relates to all diseases, crop types and management systems.
For this edition of the Agronomy Geeks podcast, I spoke with Randy Kutcher, associate professor with the Crop Development Centre at the University of Saskatchewan. In this interview, we cover what erosion and breakdown of resistance means, if all pathogens are susceptible to resistance and, most importantly, the tools farmers and agronomists have on hand to maintain the longevity of these all-important disease management tools.