Eicosapolyenoic fatty acids induce defense responses and resistance to Phytophthora capsici in tomato and pepper

Phytophthora capsici is a difficult to manage broad host-range oomycete that attacks members of the Solanaceae, Cucurbitaceae and Fabaceae. Induced resistance could complement host genetic resistance and chemical and cultural strategies to help mitigate diseases caused by P. capsici. The eicosapolyenoic fatty acids (EP), arachidonic (AA) and eicosapentaenoic (EPA) acids, are common fatty acids in oomycetes and are released from Phytophthora species during infection of plants. EP act as elicitors, or microbe-associated molecular patterns (MAMPs), triggering dramatic changes in oxylipin biochemistry and various defenses in tomatoes and peppers. Treatment of roots of hydroponically-grown tomato and pepper seedlings with 10 mu M EP induces resistance to subsequent infection with P. capsici, reducing rot and collapse at the crowns by >50%. Exposure of tomato roots to EP elicits lignification in roots within 72 h and primes the crowns for an amplified lignification response following attack by P. capsici. Tomato seedling growth is inhibited on 100-200 mu M AA-infused growth media, a high concentration of the elicitor, but a feature also observed with other studied MAMPs. Understanding the signal-response coupling and physiological costs vs. benefits of EP-triggered resistance will guide the use of EP-containing commercial products for plant protection in production systems.