Characterization of benzimidazole-resistant strains of rhynchosporium-secalis

Benzimidazole-resistant mutants of Rhynchosporium secalis were easily generated in the laboratory using UV mutagenesis. Three levels of resistance were identified (low, LR; moderate, MR; high, HR), but there was no negative cross-resistance with N-phenylcarbamate fungicides. In all cases pathogenicity was reduced, in some cases drastically. Benzimidazole-resistant field strains were first detected in 1990, some 15 years after this fungicide group was first used in UK barley crops. Unlike laboratory mutants, only HR phenotypes were isolated from the field, and all showed negative cross-resistance to N-phenylcarbamates. These field resistant strains were no less pathogenic than wild-type ones. Carbendazim binding to tubulin-like protein from HR phenotypes, whether generated in the laboratory or isolated from the field, was reduced.