THE EFFECTS OF TRICYCLAZOLE, PYROQUILON, PHTHALIDE, AND RELATED FUNGICIDES ON THE PRODUCTION OF CONIDIAL WALL PIGMENTS BY PENICILLIUM AND ASPERGILLUS SPECIES

Nine compounds that inhibit 1,8-dihydroxynaphthalene (DHN)-melanin biosynthesis in Pyricularia oryzae were used to study their effect on pigment production in conidial walls of 11 Penicillium and 5 Aspergillus species. Conidial pigmentation in all of the fungi except A. flavus and A. parasiticus was inhibited by tricyclazole and, where tested, by most of the other compounds that inhibit melanin synthesis in Py. oryzae. The stronger inhibitors of DHN-melanin synthesis (tricyclazole, chlobenthiazone, and pyroquilon) were the strongest inhibitors of pigment synthesis by the Penicillum and Aspergillus species, and four of the other compounds (phthalide, PCBA, PP-389, and MQ) had a similar order of effect on pigment synthesis in the Penicillium and Aspergillus species as previously reported for melanin synthesis in Py. oryzae. Two of the weakest melanin inhibitors, coumarin and TQ, did not inhibit pigment synthesis. Flaviolin, a shunt product from the DHN-melanin pathway, was isolated from tricyclazole-treated cultures of 10 of 14 of the fungal isolates when they were grown on a special alkaline medium. Conidial wall pigmentation was inhibited by tricyclazole in the alkaline medium, and the effects of tricyclazole on conidial wall pigmentation and flaviolin accumulation occurred concurrently. These findings indicate that some of the Aspergillus isolates and all of the Penicillium isolates used in this study contain a reductase enzyme(s) that is involved in the biosynthesis of green pigments and that is inhibited by compounds that prevent DHN-melanin biosynthesis in a number of brown to black fungi. The accumulation of flaviolin in cultures containing tricyclazole suggests that pentaketide metabolites are used in the synthesis of these pigments. (C) 1995 Academic Press, Inc.