Leveraging Resilient Lodgepole Pine Populations to Mitigate Mountain Pine Beetle Fungal Damage in Northern Forests

Climate change in western North America has facilitated the northward expansion of mountain pine beetle (Dendroctonus ponderosae, MPB) outbreaks in lodgepole pine (Pinus contorta) forests, with fungal symbionts (Grosmannia clavigera and Ophiostoma montium) playing a central role in overcoming host defences. Unlike mechanically induced beetle damage, these fungi interact directly with host chemical defences, effectively hijacking host biochemistry and immune responses. Despite their central role in determining forest vulnerability and resilience, MPB-associated fungi have rarely been studied independently of the beetle. 

We investigated how phloem chemistry from three lodgepole pine subspecies—P. contorta subsp. murrayana (Oregon), subsp. latifolia (Alberta), and subsp. contorta (British Columbia)—affected symbiotic fungal growth and volatile emissions. The experiment grew fungi under host chemical conditions representative of the three pine populations and measured fungal biomass and volatile emissions to assess fungal performance. 

Results showed that coevolved Oregon chemistry exerted the strongest suppression of fungal growth, whereas British Columbia chemistry, despite long-term beetle exposure, produced minimal inhibition. Alberta chemistry, representing evolutionarily naïve northern populations, were moderately inhibitory but stimulated the highest production of (–)-verbenone and cis-grandisol, compounds negatively associated with fungal growth and which may serve as indicators of lodgepole pine’s suppressive capacity. In contrast, isobutanol was elevated under British Columbia and control conditions, suggesting a positive association with fungal growth.

Overall, coevolved chemical defences provided greater resistance to MPB-associated fungi than naïve northern chemistry, highlighting population-specific chemical defences and informing management strategies to enhance forest resilience under ongoing MPB expansion.