FENPROPIMORPH - A 3 SITE INHIBITOR OF ERGOSTEROL BIOSYNTHESIS IN NECTRIA-HAEMATOCOCCA VAR CUCURBITAE

The effect of fenpropimorph, fenpropidin, tridemorph, pyrifenox, triadimenol, and tebuconazole on growth and sterol synthesis of a wild-type strain of Nectria haematococca var. cucurbitae was studied. Fenpropimorph-treated mycelia showed a dose dependent drop in ergosterol content with a parallel accumulation of Δ8-sterols, Δ14-sterols, and squalene, indicative of inhibition of three different enzymes in the sterol biosynthetic pathway: Δ8-Δ7-isomerase, Δ14-reductase, and squalene epoxidase. Untreated mycelia incorporated [14C]acetate into 4-desmethyl sterols, composed primarily of ergosterol, whereas in fenpropimorph-treated mycelia the label accumulated in squalene and a reduction of C-4 desmethyl sterols was observed. Fenpropidin was found to be a potent inhibitor of Δ8-Δ7-isomerase and Δ14-reductase, while tridemorph specifically inhibited Δ8-Δ7-isomerase. Triadimenol, pyrifenox, and tebuconazole inhibited the C-14 demethylation step, which resulted in a decrease in ergosterol and an increase in C-14 methyl sterols. © 1991.