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The Nature and Role of Host Defenses in Forest Pest Invasions: A Case Study Using Emerald Ash Borer (Agrilus planipennis)

Showalter, David N
http://orcid.org/0000-0001-9853-4905
http://rave.ohiolink.edu/etdc/view?acc_num=osu1481727081503819

Abstract Details

2017, Doctor of Philosophy, Ohio State University, Plant Pathology.
Emerald ash borer (Agrilus planipennis, EAB) is causing massive ecological and economic damage as it devastates North American ash (Fraxinus spp.) populations. Resistance of its coevolved hosts is thought to limit EAB outbreaks and ash mortality in its native Asia, but an understanding of resistance mechanisms is still developing. The research reported in this dissertation provides new understanding of host defenses in the EAB-ash system, in regards to both their nature (chemical or biological identity and function) and role (contribution to larval performance and tree survival), in part as a case study for a larger group of tree killing invasive pests. In Chapter 2 I argue that once exotic bark- and wood-boring insects, as well as canker- and wilt-inducing pathogens, are recognized as newly established and damaging, work should begin to transition forests into “defense-constrained space” by developing host resistance. In Chapter 3 I describe the use of controlled egg inoculations to show lower rates of larval survival and development in coevolved Manchurian ash (F. mandshurica) compared to evolutionarily naive white ash (F. americana). Water stress imposed on the host trees increased larval performance in Manchurian ash, with no significant effect on the already more susceptible white ash. These results show that the higher EAB resistance of Manchurian ash results from phloem traits that decrease larval performance, in addition to the previously documented lower oviposition preference. In Chapter 4, I build on the idea that the pro-oxidant potential of ash phloem may be associated with resistance to EAB larval feeding. I profiled phloem phenolics and pro-oxidant enzyme activities in response to EAB larval feeding in susceptible white and resistant Manchurian ash, and found novel patterns of verbascoside-related chemistry. Additionally, the results of this study have informed a revised hypothesis emphasizing the importance of pro-oxidant-associated peroxidase activities more than polyphenol oxidase and ß-glucosidase activities in ash resistance to EAB. In Chapter 5, I describe patterns of gene expression in response to EAB larval feeding in resistant Manchurian and susceptible white ash. I found little support for a previous hypothesis of impaired recognition and signaling in susceptible ash species, but also identified a rich complement of transcription factors requiring further analysis. Expression results support the association of proteins in the major allergen Bet v 1 family with ash resistance to EAB. New mechanisms for further investigation relating to EAB resistance suggested by this study include lectin binding and phosphorylation, oxidoreductase activity, leucine-rich repeat transmembrane protein kinase (LRRTK) activity, and terpene synthase activities.
Pierluigi Bonello (Advisor)
Donald Cipollini, Jr. (Committee Member)
Daniel Herms (Committee Member)
Jason Slot (Committee Member)
Guo-liang Wang (Committee Member)
153 p.
Entomology; Forestry; Plant Pathology

Recommended Citations

Citations

  • Showalter, D. N. (2017). The Nature and Role of Host Defenses in Forest Pest Invasions: A Case Study Using Emerald Ash Borer (Agrilus planipennis) [Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1481727081503819

    APA Style (7th edition)

  • Showalter, David. The Nature and Role of Host Defenses in Forest Pest Invasions: A Case Study Using Emerald Ash Borer (Agrilus planipennis). 2017. Ohio State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1481727081503819.

    MLA Style (8th edition)

  • Showalter, David. "The Nature and Role of Host Defenses in Forest Pest Invasions: A Case Study Using Emerald Ash Borer (Agrilus planipennis)." Doctoral dissertation, Ohio State University, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=osu1481727081503819

    Chicago Manual of Style (17th edition)

osu1481727081503819
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This open access ETD is published by The Ohio State University and OhioLINK.