Effect of fenpropimorph and imazalil on sterol biosynthesis in penicillium italicum

Fenpropimorph was found to be highly active against Penicillium italicum (EC50 0.01/μg ml−1). Conidia of P. italicum, treated with low concentrations of fenpropimorph, swelled in size and showed distorted germ tubes. During the initial stages of mycelial growth, fenpropimorph had little or no effect on the dry weight increase, which became strongly inhibited within 24 h after addition of the toxicant (0.05, 0.1 and 0.2 μg ml−1). Irregular deposition of β–1,3 and β–1, 4 polysaccharides, probably chitin, was observed after treatment with fenpropimorph or imazalil. Fenpropimorph (0.05 and 0.2 μ ml−1) caused the accumulation of a major demethyl-sterol that was different from ergosterol. It was identified as ergosta-8, 14, 24(28)-trien-3β-ol by mass, infrared, ultraviolet and proton nuclear magnetic resonance, spectrometric procedures. At both concentrations, the accumulation was already detected after incubation for 2 h. In contrast, imazalil (0.1 μg ml−1) caused the accumulation of several methyl- and dimethyl-sterols which were tentatively identified as eburicol (24-methylene-24, 25-dihydrolanosterol), 4, 14α-dimethylergosta-8, 24(28)-dien-3-one, 14α-methylergosta-8, 24(28)-dien-3-one and obtusifoliol (4, 14α-dimethylergosta-8, 24(28)-dien-3α-ol). The accumulation of ergosta-8, 14,24(28)-trien-3β-ol indicates inhibition of the Δ14-reductase in P. italicum in a similar manner to that found previously in Ustilago maydis.