Graduate Thesis Or Dissertation


Characterization of Fungal Endophyte Populations in Ponderosa Pine (Pinus ponderosa) Needles in The B&B Fire Complex of The Eastern Cascade Mountain Range Public Deposited

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  • Forests are some of the most ecologically diverse and dense habitats on the planet. Research shows that the endophyte community, or the fungi, bacteria, and viruses within a forest ecosystem is highly diverse. Fungal endophytes are defined as fungi that live within the tissues of host plants. Relationships between fungal endophytes and their hosts exist along a continuum from mutualism and commensalism to pathogenic. Although the most common type of relationships are commensalisms of unknown effect, endophytes offer their hosts many benefits such as protection against other pathogenic microorganisms. In fact, the forest microbiome offers a wealth of untapped potential with regards to understudied or even undiscovered fungal endophytes with best estimates for total fungal endophytes around 1 million distinct species. In this study one-, two-, and three-year-old needles were collected from trees in stands of varying burn severities (i.e., unburned, low, moderate, high) within the Jack Creek Drainage of the Eastern Cascade Mountain range. Collected needles were surface sterilized, cut into three sections of equal size, and plated on malt extract agar (MEA). A resulting 346 pure fungal cultures were obtained and organized into 27 morphologic groups. Random subsamples of each group were chosen for Sanger sequencing. General linear models were used to find differences in odds ratios and total counts of fungal endophytes across burn severities and needle age classes. Fungal isolates were plated in dual cultures to characterize in vitro interactions between each pair and antagonism index scores were calculated for each isolate. Fungi identified include Lophodermium sp., Sydowia polyspora, and Penicillium chrysogenum. Fungal endophyte infection rates of ponderosa pine needles increased with needle age and differed between burn severities. The odds of three-year-old needles being infected with fungal endophytes were estimated to be 75.9 (p < 0.001) times those for one-year-old needles and 2.91 (p < 0.001) times those of two-year-old needles. The odds of two-year-old needles being infected with fungal endophytes were estimated to be 26.0 (p < 0.001) times those of one-year-old needles. Three-year-old needles had an estimated 685% more fungal endophytes than one-year-old needles (p < 0.001) and two-year-old needles had an estimated 505% more fungal endophytes than one-year-old needles (p = 0.002). No significant difference in total endophytes were found between two- and three-year-old needles. Non-metric multi-dimensional scaling (NMS) coupled with multi-response permutation procedures (MRPP) revealed differences in fungal endophyte communities between high and unburned sites, high and low burned sites, and between one-, two-, and three-year-old needles. These tests showed that differences in odds, endophyte counts, and community structure were mainly a consequence of needle age. A variety of interactions were observed in dual cultures. Over 50% of all interactions resulted in inhibition of growth of one or both participants. This research adds to the collective knowledge of fungal endophytes in ponderosa pine needles and corroborates findings of previous studies regarding ponderosa pine needle fungal endophyte community composition.
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