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

Abstract

Potato tuber discs and foliage of cv. Kennebec (R1) 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 μg/disc stigmasterol or β-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 μg/disc arachidonic acid (AA) induced resistance to the compatible race. Application of stigmasterol or β-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 β-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.