Purdue University Graduate School
French Dissertation_12-4-2018 final.pdf (4.39 MB)


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posted on 2019-01-17, 13:56 authored by Elizabeth A. FrenchElizabeth A. French
Plants regulate responses to their environment through complex hormone signaling; these hormones can be categorized broadly into two categories: growth and defense, though many have roles in both. Much remains to be understood about the complexity of hormone signaling in relation to environmental responses, especially species- and genotype-specific differences. Unraveling this complexity of hormone signaling will lead to the development of resilient crops that are able to respond appropriately to their environment. In this dissertation, I hypothesize novel roles for growth and defense hormones in Solanum spp. responses to 1) biochar, a black carbon soil amendment (Chapter 2), 2) infection with Ralstonia solanacearum, an economically important soilborne pathogen causing bacterial wilt (Chapter 3), and 3) endophytic colonization by the soil bacterial community (Chapter 4). In Chapter 2, I showed that biochar upregulates GA signaling and affects GA-related traits in a species- and cultivar-specific manner. Biochar amendment also downregulates defense signaling. In Chapter 3, I demonstrated a novel role for auxin in resistance against R. solanacearum, including differential expression of auxin signaling genes in resistant genotype H7996 compared to susceptible WV in response to R. solanacearum infection. In addition, I observed stronger and faster upregulation of defense hormone marker genes for SA and ET in H7996 compared to WV. In Chapter 4, I showed that SA and ET are required for normal tomato root microbial community assembly, affecting the colonization of a few key taxa in order to promote alpha diversity. H7996 and WV root communities differ in alpha diversity, and a panel of H7996 x WV RILs showed quantitative variation in alpha diversity that correlated negatively with the abundance of these key taxa. In conclusion, I elucidated novel roles for hormones in responses to the soil environment, pathogen infection, and root community colonization. These findings are important for developing resilient, sustainable crops.


Degree Type

  • Doctor of Philosophy


  • Botany and Plant Pathology

Campus location

  • West Lafayette

Advisor/Supervisor/Committee Chair

Anjali Iyer-Pascuzzi

Additional Committee Member 2

Tamara Benjamin

Additional Committee Member 3

Lori Hoagland

Additional Committee Member 4

Kevin Gibson

Additional Committee Member 5

Tesfaye Mengiste