EFFECTS OF PRUNING YOUNG SCOTS PINES ON HOST VIGOR AND SUSCEPTIBILITYTO LEPTOGRAPHIUM-WINGFIELDII AND OPHIOSTOMA-MINUS, 2 BLUE-STAIN FUNGIASSOCIATED WITH TOMICUS-PINIPERDA

In a field experiment in central Sweden, the vigour of 25-yr-old Scots pines was manipulated by pruning, prior to inoculation with Leptograp hium wingfieldii and Ophiostoma minus two blue-stain fungi associated with Tomicus piniperda. Our main purpose was to correlate fungus invas ion and host defence reactions with host vigour. Both fungi invaded th e inner bark and the sapwood at the points of inoculation. L. wingfiel dii caused larger lesions in the bark, but 0. minus tended to grow fas ter in the sapwood. The flow of primary resin was related to tree vigo ur, whereas carbohydrates present in needles and stem phloem were not. Lesion formation and the content or composition of resin acids in les ions did not differ between fungi or pruning treatments.