Sphaeropsidone and episphaeropsidone, phytotoxic dimedone methyl ethers produced by Sphaeropsis sapinea f. sp. cupressi grown in liquid culture

Two phytotoxic dimedone methyl ethers, named sphaeropsidone and episphaeropsidone, were isolated from Sphaeropsis sapinea f sp. cupressi, a phytopathogenic fungus causing a canker disease of Italian cypress (Cupressus sempervirens L.). The same fungus produced the sphaeropsidins A, B and C, which are three phytotoxins recently chemically characterized as pimarane diterpenes. Sphaeropsidone and episphaeropsidone were characterized, using essentially spectroscopic methods, as two new phytotoxic disubstituted 7-oxabicyclo[4.1.0]hept-3-en-2-ones, which are epimers at C-5. Assayed on severed twigs of cypress, sphaeropsidone caused browning and necrosis on Cupressus macrocarpa, no symptoms on C. sempervirens and chlorosis on C. arizonica. Episphaeropsidone caused necrosis on C. macrocarpa, browning and necrosis on C. sempervirens and necrosis on C. arizonica. On the non-host plant tomato, both phytotoxins caused wilting. In a microbial assay, both compounds showed an inhibitory effect on the growth of five fungal species tested. The growth of Vertcillium dahliae was enhanced by both dimedone methyl ethers. (C) 1998 Elsevier Science Ltd. All rights reserved.