Comparative antifungal effect and mode of action of tetraconazole on Ustilago maydis

Tetraconazole, a new, recently introduced antifungal triazole, has been assayed in parallel with a number of standard analogues on various sensitive strains of Ustilago maydis. The values of EC50 and EC90 tetraconazole concentrations, determined on strain ATCC 14826 in agar, were 0.5 × 10-6 and 3.5 × 10-5 m, respectively, in reasonable agreement with those needed to inhibit by 50% and 90%, respectively, the ergosterol biosynthesis in broth cultures. Squalene and 12 sterols have been extracted from the latter, characterized and quantified. Accumulation of 14α-methylsterols and reduction of ergosterol and other late precursors are consistent with the inhibition of 14α-demethylase caused by the title compound.