Phytophthora infestans (Mont.) deBary was inoculated in the center of a cut slice of potato tuber, and incubated at 20℃ for 6 days. The content of ascorbic acid, both in the diseased and in the healthy parts, was determined by the Indophenol method. As resistant variety, Kennebec, as susceptible variety, Danshaku-imo were used.
Total and oxidized ascorbic acid in both varieties increased in the diseased area, but reduced ascorbic acid decreased in Danshaku-imo and in creased in Kennebec in the diseased parts. These results coincide with that of histochemical investigations on fixed materials by absolute alcohol, silver nitrate and acetic acid.
As the ascorbic acid in the mycellum is of very low percentage it seems more natural to consider that the ascorbic acid in the diseased portions is derived from the penetrated fungus mycelium but comes from the abnormal metabolism of potato tuber according to the invasion of Phytophthora infestans.
Some discussions were undertaken as to the distribution of ascorbic acid in the fungus parts and the behavior of fungus mycelium to potato tubers, having different susceptibility to the lateblight fungus.