Toxicity of rishitin, rishitin-M-1 and rishitin-M-2 to Phytophthora infestans and potato tissue.

Abstract

Rishitin and rishitin metabolites were tested for their antifungal activities to spore germination and mycelial growth of Phytophthora infestans, and for toxicity to potato tuber tissues. The antifungal activities of rishitin-M-1 and rishitin-M-2 to races 0 and 1 of P. infestans were about one tenth that of rishitin. Treatment of tuber tissue C.V. s Rishiri, Irish cobbler and Pentland ace with rishitin caused injury and darkening of the treated tissue at about 5×10-3M, but treatments with rishitin-M-1 and rishitin-M-2 had little effect on the tuber tissue even at 10-2M, the highest concentration tested. Little difference in the toxicities to the fungi and the tuber tissue was observed between rishitin-M-2 and its epimer: (11S)- rishitin-M-2. These results suggest that metabolism of rishitin to rishitin-M-1 and rishitin-M-2 may protect the healthy potato tissue from toxic effect of accumulated rishitin. These phenomena suggest that a mechanism exist in healthy plant tissue for the detoxification of the phytoalexin.