Cyclopaldic Acid, A Major Phytotoxic Metabolite of Seiridium-cupressi, the Pathogen of A Canker Disease of Cypress

A phytotoxic substance was produced in vitro in a relatively high concentration (c. 40 mg/l) by Seiridium cupressi, a fungus that causes a canker disease of cypress (Cupressus sempervirens) and other Cupressaceae in Greece and in other parts of the world. Structural investigations demonstrated that the substance was identical with cyclopaldic acid, an antibiotic known to be a metabolite of some species of Penicillium, Aspergillus and Pestalotiopsis. Absorbed by severed twigs of three species of Cupressus and by cuttings of two herbaceous non-host plants (tomato and mung bean), cyclopaldic acid at concentrations of 10-100 mug/ml induced leaf chlorosis and necrosis. Oat seed germination and root growth of oat seedlings were also reduced to about 50% at 75 and 100 mug/ml, respectively. The compound showed antifungal activity towards species of Botrytis, Fusarium and Geotrichum when assayed at a concentration range from 10 to 100 mug/ml. We believe this to be the first report of cyclopaldic acid as a non-selective fungal phytotoxin. However, its possible role in the pathogenesis of the cypress canker disease has not been established.