VIEW ARTICLE

Physiology and Biochemistry

Differences in Phytoalexin Elicitation by Phytophthora infestans and Helminthosporium carbonum in Potato. Michael N. Zook, Graduate research assistant, Department of Plant Pathology, University of Kentucky, Lexington 40546; Joseph A. Ku?, Professor, Department of Plant Pathology, University of Kentucky, Lexington 40546. Phytopathology 77:1217-1220. Accepted for publication 27 March 1987. Copyright 1987 The American Phytopathological Society. DOI: 10.1094/Phyto-77-1217.

Living spores and mycelia of Helminthosporium carbonum and an incompatible race of Phytophthora infestans elicited the accumulation of rishitin and lubimin in potato tuber disks. The same inoculum from H. carbonum lost the ability to elicit rishitin and lubimin after heat, ethanol, or liquid N₂ treatment, but spores and mycelia of P. infestans retained eliciting activity after heat or ethanol treatment. Gas chromatography-mass spectrometric analysis of extracts of H. carbonum mycelium failed to detect the presence of arachidonic or eicosapentaenoic acid, fungal elicitors from P. infestans. Inoculation with living spores of H. carbonum or application of arachidonic acid inhibited steroid glycoalkaloid accumulation, but application of dead spores of H. carbonum did not. Inoculation with either sporangia or zoospores of a compatible race of P. infestans suppressed rishitin and lubimin accumulation in response to a second inoculation with zoospores of an incompatible race of P. infestans but not in response to inoculation with spores of H. carbonum or application of arachidonic acid. The suppression by P. infestans is not likely due to inhibition of the pathway for the synthesis of rishitin and lubimin.