Mutation of Fungicide Tolerance in Fusarium spp.

Strains of Fusarium, causal fungi of scab disease of cereal crops, were examined for the mutation of topsin tolerance. The mutation rate of topsin tolerant spores was 10-5~10-6 and was not affected by the irradiation of ultraviolet rays nor application of topsin to the culture medium. Highly tolerant strains were easily selected on the screening medium containing topsin. Finally topsin was not effective to the selected tolerant mutants. The topsin tolerance was parallel to "benrate" tolerance. The tolerance was transmitted through hyphae, conidium and ascospore. The growth rate of hyphae of the tolerant mutants was lower than that of the original strains, but the conidia formation and the virulence of the mutants were comparable to the original strains. Since the heavy application of fungicides may increase the fungicide-tolerant mutants, crop varieties resistant to scab disease must be developed.