Competitive Advantage of Geosmithia morbida in Low-Moisture Wood May Explain Historical Outbreaks of Thousand Cankers Disease and Predict the Future Fate of Juglans nigra Within Its Native Range

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.

Functional roles of nematodes associated with the walnut twig beetle and eastern black walnut in the inland northwest

“…It is also important to note that although nematodes had a significant effect on necrotic area, a large amount of residual variation in canker size was documented, particularly in the experiments with Panagrolaimus sp. This result has important implications for tree‐improvement research as it corroborates previous work demonstrating that environment and host genetics (both inter‐ and intraspecies) account for a large amount of variation in the severity of TCD (Utley et al, 2013; Williams & Ginzel, 2021).…”

“…Panagrolaimus sp. This result has important implications for treeimprovement research as it corroborates previous work demonstrating that environment and host genetics (both inter-and intraspecies) account for a large amount of variation in the severity of TCD (Utley et al, 2013;Williams & Ginzel, 2021).…”

“…Fungal antagonists such as Trichoderma spp. also have a competitive advantage over G. morbida in such humid conditions (Williams & Ginzel, 2021), which would be further promoted by the nematode feeding preferences that we observed. (Fukuda, 1997;Kuroda, 1991;Yazaki et al, 2017), and/or tyloses, which are known to occur in J. regia with apoplexy disorder (McElrone et al, 2010).…”

“…4: Completely senesced 3: Crown > 50% leaves fully wilted or > 75% leaves partly wilted/yellow 2: Between 25 and 75% of leaves at least partly yellow/brown 1: Some proximal leaflets wilted or yellow 0: Healthy, no yellowing or defoliation southwest WA and northern ID could also account for differences in nematode communities as well as the severity of TCD between the two areas (Williams & Ginzel, 2021). Some members of the genus Panagrolaimus are freeze-tolerant and can survive extended periods of anhydrobiosis, surviving up to 8.7 years in dormancy (Aroian et al, 1993).…”

Spatiotemporal trends of black walnut forest stocking under climate change

“…Black walnut is sensitive to warmer-drier summers and extreme weather events (Gauthier and Jacobs, 2011). In addition, the threat of thousand-canker disease in black walnut may be increased under future climate scenarios (Williams and Ginzel, 2021). Therefore, developing a model to predict the stocking of black walnut with current and future climate data is important for prioritizing adaptive forest management in response to climate change.…”