Mutational tolerance to carbendazim in Botrytis cinerea

SUMMARY No spontaneous mutation for tolerance to the fungicide carbendazim was detected in C. 108 conidia from each of eight carbendazim‐sensitive field isolates of Botrytis cinerea. Conidia of B. cinerea were highly insensitive to u.v.‐irradiation, although after severe irradiation treatments mutant strains showing the same levels of tolerance as two groups of carbendazim‐tolerant field isolates were selected at frequencies of between 10‐9 and 10‐6 of survivors. Mutants with low levels of tolerance (ED50 > 10 μg ml‐1 carbendazim; ‘partially‐tolerant’) were selected from irradiated conidia obtained from sensitive field isolates and a further series of mutants capable of growth on 10 000 μg ml‐1 carbendazim (‘fully‐tolerant’) were selected from irradiated conidia from either partially‐tolerant mutants or from partially‐tolerant field isolates. Both mutation steps were confirmed in similar experiments in which tolerance to an unrelated fungicide, 2, 6‐dichloro‐4‐nitroaniline (DCNA), was incorporated as a genetic marker in the parent strains.