Sensitivity of populations of Botrytis cinerea to triazoles, benomyl and vinclozolin

Sensitivity of field isolates (121) of Botrytis cinerea from France (1992), Germany (1979-1992), Israel (1990) and the Netherlands (1970-1989) to the triazoles tebuconazole and triadimenol, the benzimidazole benomyl and the dicarboximide vinclozolin were tested in radial growth experiments. Resistance to benomyl (in 21 to 100% of isolates tested) and vinclozolin (in 25 to 71% of isolates tested) was common in most countries. EC(50)s (concentrations of fungicides inhibiting radial mycelial growth of B. cinerea on B5-agar by 50%) for tebuconazole and triadimenol ranged between 0.01-1.64 and 0.4-32.6 mu g ml(-1), respectively, and were log-normally distributed. The variation factor (ratio between EC(50)s of the least and most sensitive isolate tested) amounts 164 and 82 for tebuconazole and triadimenol, respectively. These values are comparable to those for azole fungicides applied in control of other pathogens. Hence, variation in sensitivity to triazoles can probably not explain limited field performance of triazoles towards B. cinerea. Isolates from south west Germany (1992) were significantly less sensitive to tebuconazole than isolates collected earlier in Germany, Israel and the Netherlands. Such less sensitive populations may contribute to the limited held performance of DMI fungicides towards B. cinerea. The sensitivity of isolates from south west Germany to tebuconazole was similar to that of DMI-resistant mutants generated in the laboratory. These mutants displayed stable resistance with Q-values (ratio between EC(50) of resistant mutant and wild type isolate) between 5 and 20. Sensitivity of field isolates and laboratory mutants to tebuconazole and triadimenol was correlated.