Date of Award

Fall 2025

Project Type

Thesis

Program or Major

Natural Resources

Degree Name

Master of Science

First Advisor

Jeffrey R. Garnas

Second Advisor

Mark Ducey

Third Advisor

Mike Simmons

Abstract

Pathogens and insects face several barriers to successful infection and colonization of a host plant, including a range of physical and chemical defenses, some of which are inducible (modified or initiated by attack or infection). These interactions can be complex and are influenced by environmental conditions, tree physiological status, host age, and timing of attack. Non-native pathogens and insects can have an advantage against a plant’s evolved chemical defenses, but they are also subject to abiotic stressors and conditions. In North America, beech bark disease (BBD) is a disease complex where the beech (Fagus grandifolia) host is subject to concurrent attack by native fungal pathogens (Neonectria faginata and Neonectria ditissima) and a non-native scale insect, Cryptococcus fagisuga. Despite over a century of research on BBD, American beech’s chemical response to BBD is understudied. This work examines the inducement of chemical response in American beech and its effect on artificially established scale and fungal colonies. Additionally, it explores the role of predator and abiotic pressures in the establishment of scale as well as the impact of fungal inoculation timing. Exogenous treatments were used to induce defense signaling cascades regulated by phytohormones commonly associated with plant response to pathogens and insects. Trees were treated to induce the salicylic acid (SA) and jasmonic (MJ) defense pathways, in addition to a combined MJ/SA induction treatment and a mock (buffer) control. Scale colonies were established according to artificial colonization methods, with a proportion of the protective ‘cages’ fully removed or modified to allow predator access. Fungal inoculation occurred in two phases: early inoculation during the dormant season and late inoculation following budbreak. The inducement experiment effectively inhibited scale colonization but had a much weaker effect on the fungal pathogens. This suggests that American beech has the capacity to effectively respond to scale insect when induced but fails to respond under control conditions. Cage modification supported previous findings that predator pressure and environmental exposure inhibit colony success. Fully exposed colonies were significantly smaller than predator access and control colonies. Fungal inoculation timing had a significant effect on lesion growth rate and overall lesion area; dormant season inoculations had a slower growth rate compared to growing season inoculations. The inability of the tree to actively respond to growing season inoculations implies it fails to chemically respond to infection by N. faginata and N. ditissima.

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