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 resi stance were identified (low, LR; moderate, MR; high, HR), but there wa s no negative cross-resistance with N-phenylcarbamate fungicides. In a ll cases pathogenicity was reduced, in some cases drastically. Benzimi dazole-resistant field strains were first detected in 1990, some 15 ye ars after this fungicide group was first used in UK barley crops. Unli ke laboratory mutants, only HR phenotypes were isolated from the field , and all showed negative cross-resistance to N-phenylcarbamates. Thes e field resistant strains were no less pathogenic than wild-type ones. Carbendazim binding to tubulin-like protein from HR phenotypes, wheth er generated in the laboratory or isolated from the field, was reduced .