DETOXIFICATION OF THE POTATO PHYTOALEXIN RISHITIN BY GIBBERELLA-PULICARIS

The ability of strains of Gibberella pulicaris to cause dry rot of pot ato tubers is related to their tolerance of the potato phytoalexin ris hitin. All highly virulent strains studied to date have proven toleran t of and able to metabolize rishitin. Here we report that a rishitin-t olerant strain metabolizes the potato phytoalexin rishitin to 13-hydro xyrishitin and 11,12-epoxyrishitin. The identity of the latter compoun d was confirmed by chemical epoxidation of rishitin. 11,12-Epoxyrishit in has no effect on the growth of a rishitin-sensitive strain and is f urther metabolized by this strain. This is the first report of a nonto xic fungal metabolite of rishitin.