Exploring how the mountain pine beetle fungal associate ophiostoma clavigerum overcomes lodgepole pine defenses

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Given increasing global trade and climate change, the ecological and economical sustainability of Canada's forests are increasingly threatened by native and alien invasive insects that carry fungal pathogens to commercial and ornamental trees. The current mountain pine beetle (MPB) epidemic in western Canada illustrates the scale of the devastating immediate and long-term effects of such epidemics, which involve specific interactions between a host, vector and pathogen. The MPB epidemic spreads by a beetle population mass-attacking lodgepole pine trees and overcoming tree defences, then reproducing in galleries under the bark. The MPB-vectored fungi are a key symbiotic component in the epidemic, because they provide essential help to the beetles in overcoming tree defences and subsequently serve as a nutrient source for the beetle progeny. When the vectored fungi have bypassed a tree's physical and chemical defenses, they rapidly colonize the tree phloem and sapwood, and kill the tree by blocking water transport to the crown. As well, the fungi stain the tree sapwood, reducing the industrial value of the wood and wood fibres. The vectored fungi are tree pathogens; they can kill trees when inoculated without the beetles. Our primary target will be the blue-stain fungus Ophiostoma clavigerum, the most pathogenic fungal MPB associate in the western Canada epidemic. Our long-term objective is to clarify the mechanisms of fungal pathogenicity. Specifically, we will identify naturally occurring oleoresin and phenolic fungicides that are the major components of lodgepole pine defence systems, and will characterize how they interfere with germination and growth of O. clavigerum. We will use biochemical and molecular approaches, taking advantage of molecular reagents generated in our previous work.