Mode of action of the fungicide flusilazole in ustilago maydis

Flusilazole is a potent inhibitor of Ustilago maydis sporidial growth (I₅₀= 20 μg liter^?1). Incorporation of ¹⁴C]acetate into ergosterol of growing sporidia is inhibited 50% by 0.5 μg liter^?1of the fungicide. Inhibition of ergosterol biosynthesis is concomitant with the accumulation of the precursors eburicol, obtusifoliol and 14α-methylfecosterol. A novel cell-free assay has been developed to measure the 14α-demethylation of ³H]dihydrolanosterol. Flusilazole inhibits the cell-free demethylation with an I₅₀of 15 μg liter^?1. These data provide strong evidence that the mode of action of flusilazole is by inhibiting ergosterol biosynthesis through direct inhibition of the 14α-demethylation of ergosterol precursors.