Variation in the virulence of Verticillium dahliae from strawberry

Isolates of V. dahliae from strawberry, tested in 1968 against cv. Cambridge Vigour, showed differences in virulence; in cvs Talisman and Cambridge Favourite there were no significant differences between plants that were inoculated and those that were not. Evidence from this experiment, and from an earlier non-replicated experiment with Cambridge Favourite, in which differences of virulence had been apparent, showed that environmental factors can cause variations in disease development that are of similar magnitude to those attributable to genetic variations in host and parasite.