RELATIONSHIP BETWEEN CHEMICAL-STRUCTURE AND BIOLOGICAL-ACTIVITY OF TRIAZOLE FUNGICIDES AGAINST BOTRYTIS-CINEREA

The inhibitory activity of commercial and experimental triazole fungic ides on the target enzyme, sterol 14 alpha-demethylase (P450(14DM)), w as studied in a cell-free sterol synthesis assay of Botrytis cinerea P ers. ex Fr. In order to assess structure-activity relationships, the i nhibitory activities of the compounds on radial growth of the fungus w ere tested as well. The EC(50) values (concentrations of fungicide inh ibiting radial growth of B. cinerea on PDA by 50%) of all triazoles te sted ranged between 10(-8) and 10(-5) M. IC50 values (concentrations o f fungicides inhibiting incorporation of [2-C-14]mevalonate into C4-de smethyl sterols by 50%) generally ranged between 10(-9) and 10(-7) M a nd correlated with inhibition of radial mycelial growth. However, diff erences in IC50 values did not reflect quantitatively the observed dif ferences in EC(50) values, since the ratio between EC(50) and IC50 inc reased with decreasing fungitoxicity. For a limited number of compound s the correlation between intrinsic inhibitory activity and fungitoxic ity was low. Both in-vitro tests were used to investigate structure-ac tivity relationships for stereoisomers of cyproconazole, SSF-109 and t ebuconazole. Fungitoxicity and the potency to inhibit cell-free C4-des methyl sterol synthesis correlated for all stereoisomers tested. Mixtu res of isomers of tebuconazole or cyproconazole were slightly less act ive than the most potent isomer. The high activity of several commerci al triazoles in both experiments implies that poor field performance o f triazole fungicides against B. cinerea is due neither to insensitivi ty of the P450(14DM) nor to low in-vitro sensitivity of the fungus.