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Specificity of Rishitin and Phytuberin Accumulation by Potato. J. L. Varns, Department of Biochemistry and Department of Botany and Plant Pathology, Purdue University, Lafayette, Indiana 47907; W. W. Currier(2), and J. Kuc(3). (2)(3)Department of Biochemistry and Department of Botany and Plant Pathology, Purdue University, Lafayette, Indiana 47907. Phytopathology 61:968-971. Accepted for publication 15 March 1971. DOI: 10.1094/Phyto-61-968.

Sonicates and boiled aqueous extracts of three races of Phytophthora infestans caused necrosis and the accumulation of rishitin and phytuberin in tuber slices. The response was observed with cultivars having R genes for resistance as well as those susceptible to all known races of the fungus. Ceratocystis fimbriata and Helminthosporium carbonum, nonpathogens of potato, also caused accumulation of rishitin and phytuberin. Solutions of chlorogenic acid, l-dihydroxyphenylalanine, catechol, dimethylsulfoxide, mercuric chloride, cupric chloride, or tyrosinase applied to the surface of slices caused necrosis without accumulation of rishitin and phytuberin. The surface of slices briefly exposed to dry ice readily browned without accumulation of the terpenoids. Necrosis accompanied by rishitin and phytuberin accumulation was evident with sprouts of four cultivars inoculated with compatible races, whereas flecking (restricted necrosis) without detection of the terpenoids was observed after inoculation with incompatible races. Rishitin and phytuberin were not detected in extracts of peel or freshly peeled tubers from eleven cultivars. Since accumulation of rishitin and phytuberin is characteristic of the incompatible interaction in tubers, a reassessment of their role as sole or primary agents responsible for restricting development of P. infestans in the entire potato plant may be necessary.