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

Abstract

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 specific biotic stress agents in tree susceptibility or resistance to the subsequent biotic attacks by insect herbivores, such as mountain pine beetle.