Conifer Chemical and Structural Defenses Against Pests and Pathogens

• Author / Creator

  Fortier, Colleen E.

• Canada’s forests are experiencing unprecedented pest and pathogen outbreaks; such instances are expected to increase under predicted climate change scenarios. A host’s ability to mount an effective defense response against pest and pathogen antagonists is dependent on recognition of the antagonist leading to the hormonal induction of molecular and biochemical defenses. Hosts that have a shared history with the antagonist are hypothesized to acquire more finely tuned defense strategies relative to naïve hosts. Defense strategies are further influenced by abiotic stresses such as water deficit, and at different stages of host development, both of which are hypothesized to alter host suitability to the antagonist.
  The overall aim of my thesis research was to investigate patterns of chemical and structural plant defenses in the interactions of conifer hosts with a suite of insect and fungal antagonists. To do so, I explored host defense responses at the molecular and biochemical level in two systems: 1) the relationship between mountain pine beetle (Dendroctonus ponderosae) and its Ophiostomatoid fungal associate, Grosmannia clavigera, in two pine species: lodgepole pine (Pinus contorta var. latifolia), which has a long-shared history with mountain pine beetle, and jack pine (Pinus banksiana), a new host and 2) the relationship between white spruce (Picea glauca) and the eastern spruce budworm (Choristoneura fumiferana).
  In my research, I found that lodgepole pine exhibit more subtle defense responses to G. clavigera than jack pine, reflective of differences in their co-evolutionary history with G. clavigera. Furthermore, water deficit alters the composition rather than the magnitude of host defense responses to G. clavigera, and lodgepole pine defense responses are influenced by water deficit to a greater extent than jack pine defense responses. Hormonal signatures of lodgepole pine defense responses reveal that G. clavigera does not contribute to overwhelming host
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  defenses during mountain pine beetle mass attack, but instead plays a role in the nutrient acquisition of developing mountain pine beetle. Lastly, during white spruce bud burst, foliar toughness is a key factor defining the phenological window of opportunity for spruce budworm feeding. My research has shown that lignin deposition is an important contributor to foliar toughness during white spruce needle development, while cuticular wax deposition is not a reliable predictor of toughness in mature white spruce.
  Together, these results demonstrate that conifer defense responses are complex and mediated by several factors. My data sheds some light on how these factors influence host suitability to pest and pathogens, important for predicting future spread and promoting effective pest management strategies within the context of a changing climate.

• Subjects / Keywords

  • plant biology
  • plant defense
  • necrotrophic pathogen
  • mountain pine beetle
  • spruce budworm
  • conifer

• Graduation date

  Fall 2022

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/r3-sjyv-2q13

• License

  This thesis is made available by the University of Alberta Library with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.