A phytotoxic pimarane diterpene of Sphaeropsis sapinea f. sp. cupressi, the pathogen of a canker disease of cypress

A phytotoxic metabolite, named sphaeropsidin A, is produced in vitro by Sphaeropsis sapinea f. sp. cupressi, a fungus that causes a canker disease of Italian cypress (Cupressus sempervirens). The spectroscopic data indicates that sphaeropsidin A is identical with a pimarane diterpenoid antibiotic previously isolated from some Aspergillus spp. When absorbed by severed twigs of three species of Cupressus and cuttings of two herbaceous plants, sphaeropsidin A at 0.1 mg ml-1 produced leaf yellowing, browning and dieback and yellowing of leaf, necrosis and epinasty, respectively. Subperidermal injection of a 0.1 mg ml-1 solution of sphaeropsidin A into young cypress trees caused longitudinal fissures and dark brown discolouration of cortical tissues. The compound showed antimicrobial activity towards 12 fungal species when assayed at a concentration range from 10 to 100 mu-g ml-1. This is the first report showing that sphaeropsidin A is a non-selective fungal phytotoxin.