Year of Award

2017

Document Type

Thesis

Degree Type

Master of Interdisciplinary Studies (MIS)

Degree Name

Interdisciplinary Studies

Other Degree Name/Area of Focus

Molecular Ecology

Department or School/College

Interdisciplinary Studies Program

Committee Chair

John McCutcheon

Committee Co-chair

Ylva Lekberg

Commitee Members

Dian Six

Keywords

whitebark pine, fungal endophytes, terpenes, Cronartium ribicola, pacific northwest, forest pathology

Subject Categories

Bioinformatics | Environmental Microbiology and Microbial Ecology | Forest Biology | Forest Management | Integrative Biology | Other Forestry and Forest Sciences | Pathogenic Microbiology | Plant Breeding and Genetics | Plant Pathology

Abstract

An invasive fungal pathogen, Cronartium ribicola (the causative agent of white pine blister rust) infects and kills whitebark pine (Pinus albicaulis) throughout the western US. Blister rust has decreased whitebark pine populations by over 90% in some areas. Whitebark pine, a keystone species, has been proposed for listing under the Endangered Species Act in the U.S., and the loss of this conifer is predicted to have severe impacts on forest composition and function in high elevations. Hundreds of asymptomatic fungal species live inside whitebark pine tissue, and recent studies suggest that these fungi can influence the frequency and severity of pathogens such C. ribicola. I used molecular methods to characterize the fungal community in whitebark pine seedlings from 21 half-sibling seed families, sourced throughout the Pacific Northwest, and grown in a common garden. I characterized endophyte communities before and after experimental inoculation with blister rust and compared community composition in susceptible vs. resistant seedlings. I also explored the defensive chemistry of these same seedlings in relation to the fungal community and overall disease severity. Seed family was the biggest driver of endophyte community composition in our common garden, but I also observed shifts in fungal communities in response to blister rust infection. Seed family identity also influenced defensive chemistry, with terpene concentration differing in resistant and susceptible seedlings. In addition, both defensive chemistry and endophyte community were correlated with characteristics of disease severity. Endophyte communities and defensive chemistry in whitebark pine that can predict disease severity may act as biomarkers of disease resistance for future breeding programs. These results suggest that the resistance to white pine blister rust observed in natural whitebark pine populations may be a combination of genetics, endophytes, and terpene composition in needle tissue, where initial interactions between the pathogen endophytes, the host take place.

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© Copyright 2017 Lorinda Bullington