Sphaeropsidins B and C, phytotoxic pimarane diterpenes from Sphaeropsis sapinea f. sp. Cupressi and Diplodia mutila

Two phytotoxic pimarane diterpenes, named sphaeropsidins B and C, were isolated from two phytopathogenic fungi causing canker diseases of Italian cypress (Cupressus sempervirens L.): Sphaeropsis sapinea f, sp. cupressi and Diplodia mutila. S. sapinea f sp. cupressi produced both phytotoxins, whereas D. mutila produced sphaeropsidins C and A, the latter also being reported as the main phytotoxin of S. sapinea f. s. cupressi. Characterized by chemical and spectroscopic methods, sphaeropsidin B proved to be a known fungal metabolite for the first time isolated from S. sapinea f. sp. cupressi, while sphaeropsidin C is a new tricyclic acid pimarane diterpene produced by both fungi. Assayed on severed twigs of cypress and oak, sphaeropsidins B and C caused dieback on C. macrocarpa, browning and necrosis on C. sempervirens and yellowing on C. arizonica, necrosis on Quercus cerri and e. ilex, and browning and necrosis on Q, robur. When injected into cortical tissues of cypress and oak seedlings mentioned above, they caused on the former dark brown discolouration, browning of internal tissues and browning, and brown-blackish spots or necrotic lesions on the latter. On non-host plants like tomato and oat, sphaeropsidins B an C caused necrosis on cuttings and brown discolouration or stewing on the stem. In the antimicrobial assay, both compounds showed an inhibitory effect on mycelial growth of seven test fungi. (C) 1997 Elsevier Science Ltd.