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Physiology and Biochemistry

Accumulation and Transformation of Rishitin and Lubimin in Potato Tuber Tissue Infected By an Incompatible Race of Phytophthora infestans. T. Horikawa, Plant Pathology Laboratory, Faculty of Agriculture, Nagoya University, Chikusaku, Nagoya, Japan; K. Tomiyama(2), and N. Doke(3). (2)(3)Plant Pathology Laboratory, Faculty of Agriculture, Nagoya University, Chikusaku, Nagoya, Japan. Phytopathology 66:1186-1191. Accepted for publication 22 April 1976. Copyright © 1976 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-66-1186.

Holes in potato tubers were filled with zoospore suspensions of an incompatible race of Phytophthora infestans. After incubation for various times, the inoculation fluids were collected and examined for inhibitory ethyl ether-soluble compounds. Rishitin, lubimin, rishitinol, and eight unknown compounds were detected by thin-layer chromatography (TLC). Rishitin, lubimin, rishitinol, and five unknown compounds were found in the inoculation fluid but not in the control fluids from healthy tubers. Rishitin levels were determined daily; the amount increased until it reached 245 μg/ml in the inoculation fluid 6 days after inoculation. Lubimin gradually increased for 96 hours to a maximum level of 28 μg/ml in the inoculation fluid. Of all the compounds detected by TLC, the rishitin spot was the largest and had the most intense color reaction, suggesting that rishitin was present in the highest concentration. Rishitin-14C was administered to healthy tubers and tubers infected by an incompatible race of P. infestans. Liquid scintillation spectrometry and autoradiography suggested that rishitin might be transformed to other compounds in both healthy and infected tissues. These results suggested that rishitin synthesized in the healthy tissue around browned tissue in tubers infected by the incompatible race would be transformed to other compounds. Thus, only a slight accumulation of rishitin occurs in the healthy tissue. In contrast, rishitin may accumulate in browned cells or in diffusates from them because of a lack of transformation.

Additional keywords: potato late blight.