Tricyclazole as an inhibitor of polyketide metabolism in the onion pink root rot pathogen, Pyrenochaeta terrestris

• Published in: Pesticide biochemistry and physiology Vol. 34; no. 3; pp. 277 - 287
• Main Authors: Lazarovits, G., Steele, R.W., Higgins, V.J., Stoessl, A.
• Format: Journal Article
• Language: English
• Published: San Diego, CA Elsevier Inc 01.07.1989; Elsevier
• Subjects: Biological and medical sciences; Chemical control; Control; Fundamental and applied biological sciences. Psychology; Fungal plant pathogens; Phytopathology. Animal pests. Plant and forest protection; Fungi; Pyrenochaeta terrestris; Anthraquinone; Mycotoxin; Pigments; Biosynthesis; Phytopathogen; Biosynthesis precursor; Fungi Imperfecti; Metabolic inhibitor; Fungicide; Thallophyta
• ISSN: 0048-3575; 1095-9939
• DOI: 10.1016/0048-3575(89)90166-1

The effect of tricyclazole on pigment production by Pyrenochaeta terrestris was investigated. Isolate LM-18 grown on amended Czapek-Dox broth or agar produced primarily the pigment cynodontin after 14 days of growth. Increasing levels of tricyclazole (1, 10, and 20 μg ml−1) inhibited cynodontin biosynthesis and resulted in the sequential accumulation of the presumed precursors emodin, chrysophanol, and helminthosporin. When grown on potato dextrose broth or agar, the fungus produced high concentrations of secalonic acids, of which isomers D and E were identified. Increasing tricyclazole levels inhibited the biosynthesis of these mycotoxins such that, at the highest level of treatment on agar medium, complete inhibition was obtained. Emodin was the only product that accumulated in these inhibited cultures. The results demonstrate that tricyclazole inhibits polyketide biosynthesis other than that related to melanin. Inhibition most probably occurs at the reductase step which converts emodin to the next intermediate product. As postulated in other studies, emodin appears to be the key intermediate in the biosynthesis of both cynodontin and secalonic acid.