Systemic resistance of potato plants against Phytophthora infestans induced by unsaturated fatty acids

Five unsaturated fatty acids were tested for their ability to induce systemic resistance in potato plants (cv. Bintje) to the late blight fungus Phytophthora infestans. Arachidonic acid and eicosapentaenoic acid applied to leaves 1-3 of potato plants at a dose of about 1 mg per plant induced 94% to 97% protection in leaves 4 to 11, respectively. Linoleic acid, linolenic acid and oleic acid provided 82%, 39% and 42% protection, respectively. Protection was evident as a reduction in lesion number and lesion diameter. It was maximal in plants challenged 5 days after induction and lasted for at least 12 days. A prior infection of lower leaves with P. infestans also induced up to 88% protection in the upper leaves. The mechanism involved in the induction of systemic resistance of potato plants by fatty acids is not understood.