EFFECTS OF DROUGHT ON THE INDUCED DEFENSE REACTION OF SCOTS PINE TO BARK BEETLE-ASSOCIATED FUNGI

Water stress was imposed on Scots pine saplings grown in a greenhouse. Predawn leaf water potential (psi(wD)) was monitored regularly while carbohydrate reserves were quantified in the phloem, xylem and shoots. Trees were inoculated in the bole with a bark beetle-associated fungus at 4 different periods of the year; the induced defence reaction was quantified 2-3 wk later by its length and the total amount of resin. A decrease in the induced reaction (length and resin quantity) was observed in the most severely stressed trees. However, no clear relationship could be established between the concentration of carbohydrates (soluble or hydrolysable) and the intensity of the defence reaction.