Abstract
AbstractMutants of Phytophthora parasitica Dast. more or less resistant to dimethomorph or metalaxyl were obtained by treating mycelium with ultraviolet radiation. Some metalaxyl‐resistant mutants exhibited levels of resistance (i.e. the ratio between the EC50 values for the mutant and the wild‐type strain) greater than 100, but those observed in the dimethomorph‐resistant mutants never exceeded 25. Most mutants retained their resistance after sub‐culturing on unamended agar medium. Single zoospore clones derived from a metalaxyl‐resistant and a dimethomorph‐resistant mutant, selected as amongst the most resistant, had levels of resistance similar to those of the parental strains. The metalaxyl‐resistant mutants were also resistant to the related phenylamide fungicides, furalaxyl and benalaxyl, but remained sensitive to dimethomorph. The dimethomorph‐resistant mutants were not resistant to phenylamide fungicides. The pathogenicity of some metalaxyl‐ or dimethomorph‐resistant mutants on tobacco leaves was similar to that of the wild‐type strains.
Published Version
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