Antifungal activity to Phytophthora infestans of sesquiterpenoids from infected potato tubers

The sesquiterpenes 2-(1',2'-dihydroxy-1'-methylethyl)-6,10(1) and its 2'-O-beta-D-glucopyranoside (2) were isolated from the stress zones of potato tubers infected with Phoma foveata and Fusarium spp., and rishitin and solavetivone from tuber slices inoculated with Erwinia carotovora. The influence of these compounds, and of the naturally occurring plant sesquiterpenoids abscisic acid, cedrol and farnesol, on the mycelial growth of Phytophthora infestans were tested on agar plates using a defined medium. All sesquiterpenoids suppressed the growth of the pathogen, except for 1 and its glucoside 2 which induced a slight, however significant, growth stimulation. Compounds 1 and 2 could not be isolated from E. carotovora or P. infestans-inoculated tuber tissue.