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Stephen Strelkov with the University of Alberta tested soil samples from 27 fields in Alberta that were seeded to resistant varieties in 2014 and showed more than expected levels of gall formation. Of those 27 fields, 15 have clubroot pathotypes that suggest the clubroot in those fields had overcome the resistance trait.
Preliminary testing indicates there may be more than one different pathotype, as scientists are not able to confirm all are 5x. Further testing is underway to determine this.
Evidence suggests that this population shift is occurring independently in individual fields. The clubroot pathogen seems to have enough diversity that within only a few years under intense canola rotations, growers quickly select for those pathotypes that are not controlled with the resistance trait.
The pathogen shift situation described at the 5:50 mark of the blackleg video is quite likely what happens with the clubroot pathogen. And because clubroot resistance appears to be a single gene trait, it seems it can be overcome more quickly than blackleg resistance.
