PATHOGENICITY TO SITKA SPRUCE OF CERATOCYSTIS-RUFIPENNI AND LEPTOGRAPHIUM-ABIETINUM, BLUE-STAIN FUNGI ASSOCIATED WITH THE SPRUCE BEETLE

The pathogenicity of the blue-stain fungi Ceratocystis rufipenni Wingf ield, Harrington & Solheim and Leptographium abietinum (Peck) Wingf., associated with the spruce beetle (Dendroctonus rufipennis (Kirby)), w as evaluated after inoculation of 35 Sitka spruce (Picea sitchensis (P ong.) Carriere) trees at densities of 200, 400, and 800 inoculation po ints/m(2) in a 60-cm band at breast height. Trees were felled 5 months after inoculation to assess fungal infection and pathogenicity. Ten t rees inoculated with C. rufipenni at the two highest densities were ra ted as dead at the time of harvesting whereas all trees inoculated wit h L. abietinum were rated as surviving or survival uncertain. Inoculat ion with C. rufipenni produced significantly longer lesions in the phl oem and killed significantly more phloem than did L. abietinum. For bo th fungi, the percentage of dead phloem increased with increasing inoc ulation density. The percentage of occluded sapwood increased with inc reasing inoculation density of C. rufipenni, and all sapwood was occlu ded at 800 inoculations/m(2). Inoculation with, abietinum resulted in approximately 25% occluded sapwood and the occlusion was not affected by inoculation density. Ceratocystis rufipenni may contribute consider ably to overwhelm spruce trees infested by D. rufipennis.