ACCUMULATION OF TEBUCONAZOLE BY ISOLATES OF BOTRYTIS-CINEREA DIFFERING IN SENSITIVITY TO STEROL DEMETHYLATION INHIBITING FUNGICIDES

Accumulation of tebuconazole by germlings of wild-type isolates of Bot rytis cinerea Pers. ex Fr. was characterized by a high initial level o f intracellular tebuconazole during the first 10 min of incubation and a subsequent gradual release of the fungicide into the surrounding me dium. This transient accumulation pattern indicates that the efflux of the fungicide has an inducible character. Accumulation of tebuconazol e by laboratory-generated mutants resistant to sterol demethylation in hibitors (DMIs) was significantly less, suggesting that efflux capacit y in these mutants is correlated with resistance. Accumulation of tebu conazole by field isolates with a relatively low sensitivity to DMI fu ngicides was transient in time and accumulation levels did not differ significantly from those of the wild-type isolates tested. These resul ts suggest that reduced accumulation of tebuconazole in fungal myceliu m may account for resistance in laboratory-generated mutants but not i n field isolates of B. cinerea with a relatively low sensitivity to th e fungicide. Various chemicals such as carbonyl cyanide 3-chlorophenyl hydrazone, copper sulfate, fluazinam and BAS 490F enhanced accumulatio n of tebuconazole by a DMI-sensitive and a DMI-resistant isolate. This enhanced accumulation is ascribed to inhibition of the energy-depende nt efflux of the fungicide.