Mutational tolerance to carbendazim in Botrytis cinerea

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 (EDsub(50)(< 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. (author)