MONOTERPENE AND PHENOLIC COMPOUND CONCENTRATIONS IN WATER-STRESSED RED PINE INOCULATED WITH SPHAEROPSIS-SAPINEA

Changes in monoterpene and phenolic compounds resulting from water str ess and colonization by Sphaeropsis sapinea were examined for 9- and I i-year-old red pine trees in a plantation and 3-year-old seedlings in a growth chamber. Four treatments were assigned at random to individua l trees in the field: no treatment, herbicide to kill surrounding weed s, supplemental water, and both herbicide and supplemental water. In t he growth chamber, seedlings were either not watered (water stressed) or watered daily (nonstressed). Shoots were inoculated with agar plugs colonized with either S. sapinea isolates of morphotype A and B (fiel d) or only isolates of morphotype A (growth chamber). Nine monoterpene s were detected in tissue extracts; the most common were alpha-pinene (59 to 74% of the total), beta-pinene (13 to 33% of the total), and de lta-3-carene (1 to 5% of the total). Shoots inoculated with isolates o f morphotype A had more severe symptoms and produced higher concentrat ions of monoterpenes in both experiments compared with the controls. I n the growth chamber, inoculations with isolates of morphotype A cause d higher concentrations of phenolics compared with the controls. In th e field experiment, monoterpenes increased in quantity only in shoots of stressed trees inoculated with isolates of morphotype A. Isolates o f morphotype B caused few symptoms and did not alter monoterpene conce ntrations. Increases in monoterpenes do not appear to be involved in t he response to infection by morphotype A in nonstressed trees, and the role of phenolics is unclear. However, these results are consistent w ith previous observations that monoterpenes may be involved in the dif ferences in aggressiveness between morphotypes an red pine.