Canadian Forest Service Publications
Fitness and pathogenicity of the fungi associated with the mountain pine beetle and other secondary beetles in green attack. 2008. Breuil, C. Natural Resources Canada, Canadian Forest Service, Pacific Forestry Centre, Victoria, BC. Mountain Pine Beetle Working Paper 2008-04. 19 p.
Available from: Pacific Forestry Centre
Catalog ID: 28161
The mountain pine beetle (MPB) (Dendroctonus ponderosae) and its fungal associates kill healthy lodgepole pine forests in western Canada and the north-western United States. In previous work we characterized the fungal associates of MPB and analyzed their phylogenetic relationships. In this work we re-assessed the identification of a few species, including O. nicrocarpum-like (now O. abietinum-like), the genera Graphium and Ambrosiella, and the O. minutum-like isolates. We also assessed the pathogenicity of five isolates of O. clavigerum and re-examined the virulence indicators for fungal pathogens. Finally, we determined the physiological characteristics of a few strains of O. clavigerum. While the work on fungal identity is not totally completed, good progress has been made and further work will be pursued in 2007-2008. We are now confident that the fungi identified as Ambrosiella sp. were in fact Ophiostoma species. The description of the epitype for O. minutum will be completed soon; the fungi originally described as O. minutum-like are more closely related to Ophiostoma manitobense. One of the MPB-associates, O. clavigerum, is pathogenic and can kill trees when inoculated in the absence of the beetle. Consequently, field studies were initiated to examine variation in virulence indicators (lesion length, moisture content and occlusion area) for five strains of O. clavigerum. These studies were necessary since only one isolate has been tested in this epidemic and because population analyses of over 100 isolates have shown different grouping of the isolates. Significant differences between strains were observed for all indicators measured. The strain SL-kW 1407, which was used most recently for testing the pathogenicity of O. clavigerum in the field, was found to be the least virulent among the five fungal strains, indicating O. clavigerum may be even more virulent than previously thought. Finally, we assessed the same five strains for the growth response to temperature variation, terpene treatment, oxygen deficiency, lipids and pH. Optimal growth was found between 22.5 to 25oC and at pH 5.5-6.0. The isolates showed reduced growth when exposed to terpenes, linoleic acid and coconut oil. The growth was inhibited by capric and myristic acids. The growth was slightly increased under anaerobic environment. Characterizing the pathogenicity and physiology of the fungi (e.g., O. clavigerum) contributes to the understanding of the MBP outbreak.
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