Variation in pathogenicity of a mountain pine beetle-associated blue-stain fungus, Grosmannia clavigera, on young lodgepole pine in British Columbia

Grosmannia clavigera is the most pathogenic blue-staining fungal associate of the mountain pine beetle (Dendroctonus ponderosae). In contrast to its importance as a primary invader of lodgepole pine (Pinus contorta) sapwood, intraspecific variability in pathogenicity of G. clavigera on lodgepole pine, the predominant host of mountain pine beetles in British Columbia, has not been investigated in detail. The present work reports on pathogenicity indicators induced by five G. clavigera isolates inoculated into lodgepole pines and growth characteristics of the isolates on artificial media. Fungi were inoculated at 200 inoculations/m² into young lodgepole pine trees. Phloem lesion length, sapwood occlusion area, and sapwood moisture content were measured after 7 or 48 weeks. Three isolates produced long lesions, occluded larger areas, and reduced more the moisture content after 48 weeks compared with the remaining two isolates. Isolate ATCC 18086 induced the strongest pathogenic symptoms after 7 weeks and grew the fastest up to 22.5 °C but grew the slowest at 27.5 °C. In a low-oxygen environment, most isolates grew faster than under ambient conditions. Significant intraspecific variation was observed among G. clavigera isolates for all parameters tested.