Abstract
Bark beetles vector symbiotic fungi and the success of these mutualisms may be limited by competition from other microbes. The outcome of fungal competition is strongly influenced by the physical and chemical conditions of the wood they inhabit. These conditions are in turn subject to climatic variation. In particular, wood moisture content (MC) influences fungal competition and, therefore, could help determine environmental suitability for thousand cankers disease (TCD) caused by Geosmithia morbida and its vector Pityophthorus juglandis. We conducted competition experiments in Juglans nigra wood that was naturally or artificially colonized by G. morbida and other fungi over a range of wood MC expected across prevailing United States climatic conditions. G. morbida outcompeted antagonistic fungi Clonostachys and Trichoderma spp. at <5% equilibrium moisture content. Aspergillus spp. outcompeted G. morbida at low moisture in wood from Indiana. We fit a logistic regression model to results of the competition experiments to predict survival of G. morbida across the United States. Expected survival of G. morbida was highest in historical TCD epicenters and accounted for the low incidence and severity of TCD in the eastern United States. Our results also predict that under future climate scenarios, the area impacted by TCD will expand into the native range of J. nigra. Given its role in emergent forest health threats, climate change should be a key consideration in the assessment of risks to hardwood resources.
Highlights
Range expansions of native pests caused by climate change are a major threat to the health and productivity of forest ecosystems (Ramsfield et al, 2016; Pureswaran et al, 2018)
Our research demonstrates that fungal competition mediated by abiotic conditions potentially limits the success and dispersal of G. morbida and adds to a growing body of evidence that environmental conditions, including abiotic factors and the host microbiome, account for the lower severity of thousand cankers disease (TCD) in the native range of J. nigra (Griffin, 2015; Seybold et al, 2019; Onufrak et al, 2020)
Our experiments suggest that the higher equilibrium moisture content (EMC) in walnut wood in the Midwest, Appalachia, and Atlantic United States limits the rates of successful establishment and spread of G. morbida due to competition with other fungi
Summary
Range expansions of native pests caused by climate change are a major threat to the health and productivity of forest ecosystems (Ramsfield et al, 2016; Pureswaran et al, 2018). Physicochemical conditions in bark and wood, including nutrient availability, temperature, and moisture, determine the outcome of competition between the primary mutualist of a beetle species and other fungi, and affect reproductive success and dispersal (Rayner and Boddy, 1988; Ranger et al, 2018). Co-dispersal of the walnut twig beetle (Pityophthorus juglandis Blackman) and its primary mutualist, the pathogenic fungus Geosmithia morbida Kolarík, Freeland, Utley, and Tisserat, to walnut trees (Juglans spp.) is contingent on physicochemical conditions that favor competitive success and sporulation of G. morbida in walnut wood. Many species of scolytine beetles have evolved specialized structures, glands, and behaviors that maximize favorability of growth conditions for the successful colonization of wood by their mutualistic fungi (FranckeGrosmann, 1967; Weed et al, 2015; Nuotclà et al, 2019). The hydrophobic spores of G. morbida are borne on conidiophores inside beetle galleries (Tisserat et al, 2009; Kolarík et al, 2011) and picked up by static adhesion to the cuticle of adult P. juglandis as they emerge (Seybold et al, 2016)
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
