EFFECTS OF BIOTIC AND ABIOTIC STRESS ON INDUCED ACCUMULATION OF TERPENES AND PHENOLICS IN RED PINES INOCULATED WITH BARK BEETLE-VECTORED FUNGUS

This study characterized the chemical response of healthy red pine to artificial inoculation with the bark beetle-vectored fungus Leptograph ium terebrantis. In addition, we sought to determine whether stress al tered this induced response and to understand the implications of thes e interactions to the study of decline diseases. Twenty-five-year-old trees responded to mechanical wounding or inoculation with L. terebran tis by producing resinous reaction lesions in the phloem. Aseptically wounded and wound-inoculated phloem contained higher concentrations of phenolics than did constitutive tissue. Trees inoculated with L. tere brantis also contained higher concentrations of six monoterpenes, alph a-pinene, beta-pinene, 3-carene, limonene, camphene, and myrcene, and higher total monoterpenes than did trees that were mechanically wounde d or left unwounded. Concentrations of these moneterpenes increased wi th time after inoculation. Total phenolic concentrations in unwounded stem tissue did not differ between healthy and root-diseased trees. Li kewise, constitutive monoterpene concentrations in stem phloem were si milar between healthy and root-diseased trees. However, when stem phlo em tissue was challenged with fungal inoculations, reaction tissue fro m root-diseased trees contained lower concentrations of alpha-pinene, the predominant monoterpene in red pine, than did reaction tissue from healthy trees. Seedlings stressed by exposure to low light levels exh ibited less extensive induced chemical changes when challenge inoculat ed with L. terebrantis than did seedlings growing under higher light. Stem phloem tissue in these seedlings contained lower concentrations o f ol-pinene than did nonstressed seedlings also challenge inoculated w ith L. terebrantis. It is hypothesized that monoterpenes and phenolics play a role in the defensive response of red pine against insect-fung al attack, that stress may predispose red pine to attack by insect-fun gal complexes, and that such interactions are involved in red pine dec line disease. Implications to plant defense theory and interactions am ong multiple stress agents in forest decline are discussed.