A Pine in Distress: How Infection by Different Pathogenic Fungi Affect Lodgepole Pine Chemical Defenses

Abstract

In North America, lodgepole pine is frequently subjected to attacks by various biotic disturbances that compromise its ability to defend against subsequent attacks by insect herbivores. We investigated whether infections of lodgepole pine by different pathogenic fungal species have varying effects on its defense chemistry. We selected two common pathogens: Atropellis canker and western gall rust, affecting mature lodgepole pine trees in western Canada. We also included three ophiostomoid fungi associated with the mountain pine beetle, Grosmannia clavigera, Ophiostoma montium, and Leptographium longiclavatum because symbiotic fungi are commonly used to investigate induced defenses of host trees of bark beetles. We collected phloem samples from lodgepole pine trees infected with the rust or the canker, and healthy lodgepole pine trees in the same stand. We also inoculated mature lodgepole pine trees with the three fungal symbionts and collected phloem two weeks later when the defense chemistry at its highest level. All samples were analyzed for their terpene composition in gas chromatograph/mass spectrometry. Different pathogenic fungal species differentially altered the terpene chemistry of lodgepole pine trees. Western gall rust and the beetle-fungal symbionts altered the tree terpene chemistry in a similar fashion while trees responded to the infection by the Atropellis canker differently. Our study highlights the importance of considering speci c biotic stress agents in tree susceptibility or resistance to the subsequent biotic attacks by insect herbivores, such as mountain pine beetle.

Unraveling the multifaceted effects of climatic factors on mountain pine beetle and its interaction with fungal symbionts

“…The mountain pine beetle (MPB, Dendroctonus ponderosae Hopkins) (Coleoptera: Curculionidae, Scolytinae), a phloem‐feeding bark beetle species, is a component of natural forest succession and ecosystem properties. It is also considered a major forest pest due to its ability to kill several pine species during intermittent outbreaks and its significant role in shaping forest species composition and ecosystem function across western North America (Bentz et al., 2010; Jactel et al., 2019; Logan et al., 2010; Pureswaran et al., 2018; Raffa et al., 2008; Robbins et al., 2022; Zaman, Antonioli, et al., 2023; Zaman, May, et al., 2023). The host tree colonization of MPB is primarily driven by its ability to aggregate on host trees and its interactions with microbial symbionts (Paine et al., 1997; Safranyik & Carroll, 2006; Wood, 1982).…”

“…Different fungal species play a crucial role in shaping the biology and determining the success of host colonization for the MPB. For instance, symbiotic ophiostomatoid fungi (Ophiostomatales, Ascomycota), including Grosmannia clavigera , Leptographium longiclavatum and Ophiostoma montium , can contribute to successful host tree colonization by acquiring nutrients and detoxifying host tree secondary metabolites (Agbulu et al., 2022; DiGuistini et al., 2011; Goodsman et al., 2012; Guevara‐Rozo et al., 2020; Lieutier et al., 2009; Ojeda Alayon et al., 2017; Six, 2012; Wang et al., 2014; Zaman, Antonioli, et al., 2023; Zaman, May, et al., 2023). In particular, as larvae feed on the phloem, they depend on these fungi to break down the complex secondary metabolites into simpler digestible forms (Ayres et al., 2000; Bleiker & Six, 2007).…”