SENSITIVITY OF POPULATIONS OF BOTRYTIS-CINEREA TO TRIAZOLES, BENOMYL AND VINCLOZOLIN

Sensitivity of field isolates (121) of Botrytis cinerea from France (1 992), Germany (1979-1992), Israel (1990) and the Netherlands (1970-198 9) to the triazoles tebuconazole and triadimenol, the benzimidazole be nomyl and the dicarboximide vinclozolin were tested in radial growth e xperiments. Resistance to benomyl (in 21 to 100% of isolates tested) a nd vinclozolin (in 25 to 71% of isolates tested) was common in most co untries. EC(50)s (concentrations of fungicides inhibiting radial mycel ial growth of B. cinerea on B5-agar by 50%) for tebuconazole and triad imenol 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 betwe en EC(50)s of the least and most sensitive isolate tested) amounts 164 and 82 for tebuconazole and triadimenol, respectively. These values a re comparable to those for azole fungicides applied in control of othe r 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 sens itive to tebuconazole than isolates collected earlier in Germany, Isra el 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 w as similar to that of DMI-resistant mutants generated in the laborator y. These mutants displayed stable resistance with Q-values (ratio betw een 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.