PATHOGENICITY TO DOUGLAS-FIR OF OPHIOSTOMA-PSEUDOTSUGAE AND LEPTOGRAPHIUM-ABIETINUM, FUNGI ASSOCIATED WITH THE DOUGLAS-FIR BEETLE

Pole-size Douglas-fir (Pseudotsuga menziesii (Mirb.) France) were inoc ulated with two fungi (Ophiostoma pseudotsugae (Rumb.) von Ant and Lep tographium abietinum (Peck) Wingf.) associated with the Douglas-fir be etle (Dendroctonus pseudotsugae Hopkins) to evaluate their pathogenici ty. Pruning the lowermost 30% of the live crown had no effect on host tree defenses. Inoculation with O. pseudotsugae produced significantly longer lesions in the phloem and resulted in a significantly greater percentage of necrotic phloem than inoculation with L. abietinum. The percentage of occluded sapwood was also greater following O. pseudotsu gae inoculations, but the difference was not statistically significant . Individual lesion lengths declined significantly with increasing ino culation density, but the total percentage of necrotic phloem increase d significantly. Both fungi appeared to be better adapted to grow in s apwood than in phloem. None of the inoculated trees were dead after 5 months, but some were chlorotic with less than 30% functional sapwood within the inoculation band. The results suggest that these fungi may assist the Douglas-fir beetle in overcoming the defenses of live trees .