THE EFFECT OF STEROLS ON THE COMPATIBILITY OR INCOMPATIBILITY OF POTATO-TUBER DISCS AND FOLIAGE TO PHYTOPHTHORA-INFESTANS AND HELMINTHOSPORIUM-CARBONUM, AND THE INDUCTION OF RESISTANCE BY ARACHIDONIC-ACID

Potato tuber discs and foliage of cv. Kennebec (Rl) exhibited incompatible interactions to race 0 or race 4 of Phytophthora infestans and a compatible interaction to race 1,2,3,4 of the Fungus. Application of 1 or 2 mu g/disc stigmasterol or beta-sitosterol prior to inoculation with an incompatible race resulted in extensive colonization. Both of the sterols were equally active on tuber discs and were most effective when applied 2 h before, or within 4 h after, inoculation. Treatment of tuber discs with 10 mu g/disc arachidonic acid (AA) induced resistance to the compatible race. Application of stigmasterol or beta-sitosterol to AA-treated discs resulted in colonization of discs by either compatible or incompatible races of P. infestans. Treatment with stigmasterol did not cause Helminthosporium carbonum, a pathogen of corn, to become pathogenic to potato tuber discs. Extensive late blight disease was evident on potato plants cv. Kennebec sprayed with stigmasterol, but not beta-sitosterol, prior to inoculation with race 0 or race 4 of P. infestans. The possible mechanisms For compatibility/incompatibility in plants and tubers as influenced by sterols are discussed. (C) 1995 Academic Press Limited.