Ergosterol biosynthesis and its inhibition by fenpropimorph in Fusarium species

In the mycelium of all the Fusarium species studied, the major sterol was ergosterol in the absence of fenpropimorph. In the presence of this fungicide fenpropimorph-sensitive strains, with the exception of F. nivale, accumulated mainly Δ 8,14-sterols and tolerant ones accumulated either both Δ 8,14- and Δ 8-sterols or only Δ 8-sterols. This seemed to indicate that fenpropimorph toxicity was related to sterol Δ 14-reductase sensitivity. In F. nivale, which was highly sensitive to fenpropimorph, the accumulation of only Δ 8-sterols indicated that the main target enzyme was sterol Δ 8→Δ 7-isomerase. In addition to Δ 8,14-and Δ 8-sterols, squalene was accumulated in very high amounts in several strains; the level of squalene accumulation did not seem to be correlated with fenpropimorph sensitivity.