For years scientists have bred clubroot-resistant canola varieities to combat the issues with the disease, but researchers have found some new virulent clubroot pathotypes that can overcome resistance.
Stephen Strelkov, a professor of plant pathology at the University of Alberta, says they have found 11 distinct strains of clubroot that have broken resistance, and since 2013, they've found 24 fields with such issues.
"They have slightly different characteristics, so that seems to suggest it wasn't just that the resistance broke down in a single field and these strains spread from there, but likely different strains have been independently kind of selected for in individual fields, distinct from each other," Strelkov says.
Strelkov says this type of effect is always a risk when it comes to genetic resistance, however farmers can prolong the longevity of clubroot resistant varities by using a longer crop rotation.
"In most cases where we have found that resistance has been defeated, the resistant canola was being grown in a short rotation, maybe one in two years, and often they had heavy clubroot infestation, so that's putting tremendous selection pressure on the pathogen to adapt to this new resistance," he says. "So if one can move out of such a short a rotation, particularly where clubroot is prevalent, that does reduce the pressure, and that will help to ensure the longevity of that resistance."
Source : Steinbachonline