Date of Award

Winter 2015

Project Type

Thesis

Program or Major

Plant Biology

Degree Name

Master of Science

First Advisor

Cheryl Smith

Second Advisor

Isabel Munck

Third Advisor

Barrett Rock

Abstract

Over the past seven years eastern white pines (Pinus strobus) across the northeastern United States have been prematurely defoliating due to a disease complex known as White Pine Needle Damage (WPND). Previous research on WPND indicates that this outbreak, which started in 2010, is primarily attributed to the causal agent of brown spot needle blight, Lecanosticta acicola along with two other known P. strobus needle cast pathogens, Bifusella linearis and Lophophacidium dooksii. The current outbreak is thought to have arisen from several consecutive years of increased temperature and precipitation in the region. Current research, however, is lacking in both sampling distribution, the basic epidemiology of the primary causal agents, and the specific climatic factors that affect the development and spread of this outbreak. Furthermore, recent re-sampling of diseased P. strobus needles within this region has revealed a high isolation frequency of a putative new species closely related to Septorioides pini-thunbergii, a species associated with needle cast of Pinus thunbergii in Japan, which was initially not known to be associated with WPND. This thesis intends to fill this lack of information, first by examining the putative new species of Septorioides through phylogenetic analysis of six gene loci (SSU, LSU, ITS, β-tubulin, EF1, and RPB2) to describe and classify its association with WPND. Secondly, by expanding field based sampling of WPND within Vermont, New Hampshire, Maine, and their neighboring states to construct a more detailed distribution map. Thirdly, by utilizing long-term WPND monitoring plots and data collected from land-based weather stations to create a climatic model to predict the severity of defoliation events in the next year. Lastly, by establishing a field-based spore trapping experiment to determine how climatic factors affect the development and dispersal of L. acicola spores. Results from this thesis demonstrate the widespread occurrence and establishment of a new family (Septorioideaceae), and a new species Septorioides strobus, as well as its association with the current WPND outbreak. Continued sampling provided further support for the disease complex theory that L. acicoa, B. linearis, L. dooksii, and S. strobus were ubiquitous across the region and neither an individual species nor a specific combination of species had a dominating presence in particular states or regions, but were generally found in forest stands that compromised >50% eastern white pine by basal area. Additionally, regional weather data confirmed the trend of increasing temperature and precipitation observed in this region with the previous year’s May, June, and July rainfall being the best predictor of the following years defoliation event, while the current year’s relative humidity was responsible for spore development and increased inoculum loads.

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