Doctor of Philosophy, Case Western Reserve University, 2022, Biology

Flax is a dual-purpose crop for both the seeds and linseed oil; as with other major crops, abiotic stress imparted by both varying environmental conditions and climate change have significant effects on the plant's viability. In particular, nutrient deprivation is well-characterized at both the phenotypic and molecular level in four varieties of flax (Bethune, Pl, S, and L). While, salt stress susceptibility and tolerance is much less understood in the aforementioned flax varieties. The primary aims of this project included: 1. characterize the phenotype and genotype of four flax varieties under salt stress to be compared to nutrient deprivation, 2. determine the transcriptomic changes of the four flax varieties under salt stress versus nutrient deprivation, and 3. characterize the flax soil microbiome (rhizosphere) to identify punitive plant growth promoting rhizobacteria (PGPR) and/or well-known PGPR. The first portion of the project focused on collecting data pertaining to several phenotypic metrics (height, branching, flowering, and seed setting/collection), as well as genotypic characteristics. Such genotypic regions of interested included LIS-1 to determine if this region was inserted under salt stress, as well as, characterize of several molecular markers (scaffold regions) to identify genotypic patterns specific to salt stress. While, the second portion consisted of RNA sequencing of Bethune, Pl, S and L under salt stress (0.08 M NaCl and 0.15 M NaCl). Additionally, RNA sequencing of S and L under nutrient deprivation was conducted. These data illustrated that many candidate transcripts are those implicated in general stress response, as there was not consistent differential expression per each stress condition within or between flax varieties. Finally, the third portion consisted of 16S ITS V4 sequencing which allowed for metagenomic analysis of the Bethune, Pl, S, and L soil microbiomes under 0.08 M NaCl, 0.015 M NaCl, and nutrient deprivation. This al (open full item for complete abstract)

Committee: Christopher Cullis (Advisor) Subjects: Agriculture; Biochemistry; Bioinformatics; Biology; Botany; Developmental Biology; Environmental Science

Master of Science, The Ohio State University, 2017, Horticulture and Crop Science

Autophagy (self-eating) is an intracellular process by which macromolecules (i.e. proteins and lipids) or entire organelles are degraded in the vacuole. Micro- and macro-autophagy have been identified in plants. The hallmark of macroautophagy (hereafter autophagy) is the autophagosome. Autophagy is regulated by the autophagy-related (ATG) genes, and it is involved in cellular homeostasis, nutrient recycling during senescence, and environmental stress responses. Autophagy deficient plants senesce prematurely, and they are hypersensitive to abiotic stresses. Premature senescence (leaf or flower) and abiotic stress damage reduce postharvest quality of floriculture crops. The goal of this project was to describe the role of autophagy in senescence and abiotic stress responses of Petunia × hybrida 'Mitchell Diploid'. Better understanding of the processes involved in senescence and abiotic stress responses may lead to the development of floriculture crops with extended leaf/flower longevity or higher abiotic stress tolerance. Petunia is an important floriculture commodity, and it is a good plant model for both senescence and abiotic stress research. Quantitative PCR was used to study how gene expression was regulated during certain developmental stages or by external factors. We analyzed how PhATG4, PhATG5, PhATG6, PhATG7, PhATG8a, and PhATG13 were regulated during age-induced flower senescence, nutrient starvation, and salt stress. All six ATG genes were expressed at basal levels in recently opened flowers and leaves from non-stressed plants. Petunia ATG genes were upregulated upon the onset of flower senescence (corolla wilting). Low fertility stress and individual nutrient (-N or -P) deficiencies increased the expression of the ATG genes. Changes in expression of the ATG genes happened within the first 24 h after salt treatment. Thus, expression of the ATG genes is regulated by flower senescence and abiotic stress responses of petunia. RNA interference (RNAi) is a co (open full item for complete abstract)

Committee: Michelle Jones (Advisor); John Finer (Committee Member); Joshua Blakeslee (Committee Member) Subjects: Horticulture

Master of Science, Miami University, 2025, Microbiology

Chlamydomonas reinhardtii is a model alga used in the study of photosynthesis. One of the attractive attributes of C. reinhardtii is its ability to grow autotrophically, heterotrophically, or mixotrophically depending on the availability of light and acetate. Due to the advantages of mixotrophic growth, many studies of the photosynthetic stress response are conducted in acetate supplemented medium, while studies conducted under autotrophic growth conditions are limited. There is evidence that even under non- stressed conditions, mixotrophically grown cultures exhibit distinct photophysiology. To describe differences in the response to abiotic stress, C. reinhardtii growth and physiology during control and long-term stress (high light, high salt, combined high light/high salt) were compared under autotrophic versus mixotrophic conditions. Photochemistry, ATP:ADP ratios, and abundance of photosynthetic proteins were measured. Higher growth rates in mixotrophic vs. autotrophic-grown cultures were accompanied by retention of photosystem II activity and higher rates of photosystem I- driven cyclic electron flow. Under long-term stress, mixotrophic cultures exhibited reduced capacity for non-photochemical quenching and increased abundance of photosystem II. We conclude that mixotrophic growth conditions significantly impact the physiology and tolerance of C. reinhardtii to stress. Trophic mode should be considered when using C. reinhardtii to study the photosynthetic stress response.

Committee: Rachael Morgan-Kiss (Advisor); Carole Dabney-Smith (Committee Member); Mitchell Balish (Committee Member) Subjects: Microbiology; Physiology; Plant Sciences

Master of Science (MS), Wright State University, 2024, Biological Sciences

Emerald ash borer (EAB), Agrilus planipennis, is an invasive pest that significantly impacts olive trees (Olea europaea). This study aimed to assess the role of abiotic stress factors such as drought and salinity in influencing plant defenses and resistance to EAB, while also examining cultivar variation in resistance. The study specifically aimed to address: (1) What effects do varying degrees of abiotic stress (drought, salinity) have on olive trees' antioxidant and peroxidase activity in olive tree? (2) Do distinct olive cultivars exhibit varying levels of resistance to EAB under various stressors? We used a controlled experimental design with two stress treatments (drought and salinity) and 20 olive cultivars to conduct the bioassay. Growth metrics (height and stem diameter), peroxidase activity, and antioxidant activity were measured, while EAB survival and performance were assessed by monitoring larval feeding and growth. Results indicated no significant differences in antioxidant activity between treatments, although low salinity slightly enhanced antioxidant responses. Peroxidase activity was highest under high salinity, and growth responses varied by treatment and cultivar, with Leccino showing the highest antioxidant activity. EAB larvae performed best under drought conditions but exhibited poor survival on certain cultivars. These findings suggest that abiotic stress influences both plant defense mechanisms and pest resistance, with cultivar-specific responses to stress and pest pressure.

Committee: Don Cipollini Ph.D. (Advisor); John Stireman III Ph.D. (Committee Member); Volker Bahn Ph.D. (Committee Member) Subjects: Agriculture; Agronomy; Biology; Botany; Chemistry; Ecology; Entomology; Environmental Science; Environmental Studies; Nutrition; Plant Biology; Plant Pathology; Plant Sciences; Public Health; Soil Sciences

Master of Science, The Ohio State University, 2024, Horticulture and Crop Science

Biostimulant products are substances made of microbial and non-microbial ingredients that benefit plant growth and health. They can be used to mitigate soil and water pollution caused by fertilizer use in plant production. Most biostimulant research has focused on agronomic crops grown in soil and little is known about the efficacy of different biostimulants in floriculture crops grown in soilless substrates. Floriculture crops are commonly grown in peat-based substrates, and their market value is dictated by their visual quality. Wilted plants are commonly seen in retail shops, where they may receive infrequent or inadequate irrigation. Water limitation affects visual quality and marketability, therefore causing economic losses for growers. Microbial biostimulants are proven to enhance plant growth and improve crop yield in some cases. These biostimulants, which include plant growth-promoting bacteria (PGPB) and arbuscular mycorrhizal fungi (AMF), have been shown to stimulate physiological processes in plants, leading to increased nutrient availability, and enhanced tolerance to abiotic and biotic stresses such as drought. Humic substances, a non-microbial biostimulant, are extracted from organic matter and have been demonstrated to enhance plant growth by increasing plant height and weight, improving nutrient uptake, and influencing various plant processes such as enzyme activity, protein metabolism, photosynthesis, increasing water and nutrient uptake, as well as improving soil structure. However, the lack of consistent results has limited the adoption of biostimulants by growers. The goal of this study was to identify biostimulants with high efficacy in floriculture crops grown in peat-based soilless substrate. This was accomplished with two objectives: (1) analyze the efficacy of humic substances at enhancing plant growth and health in floricultural crops produced in soilless substrate and (2) determine how pH and fertility levels influence the efficacy of micr (open full item for complete abstract)

Committee: Michelle L. Jones (Advisor); Chieri Kubota (Committee Member); Matt Kleinhenz (Committee Member); Garrett Owen (Committee Member) Subjects: Agriculture; Horticulture; Plant Sciences

Doctor of Philosophy, The Ohio State University, 2021, Horticulture and Crop Science

Plant breeders have used wild relatives as a source of genetic diversity for biotic and abiotic stress mitigation since the early 20th century. This natural allelic diversity is a vital resource for crop improvement. The focus of this dissertation was to use tomato as a model to compare two methods of accessing trait diversity from wild relatives: introgression breeding and grafting. The specific aims were to estimate the genetic and environmental contributions to trait delivery methods and assess their relative efficacy and limitations. An accession of the endemic Galapagos tomato, S. galapagense LA1141, provided allelic variation for the genetic dissection of purple fruit pigmentation and tolerance to water deficit stress. Accessions of S. pimpinellifolium and S. habrochaites were used as parents to develop interspecific hybrid rootstock for multi-year, multi-location field trials. The first objective was to determine the chemical and genetic basis of purple pigmentation. Accession LA1141 and a processing tomato, OH8245, were used to develop populations for the simultaneous characterization and introgression of traits. The breeding strategy employed repeated backcrossing (BC) followed by inbreeding (S). The LA1141 × OH8245 populations provided plant materials to identify genetic factors that underlie quantitative trait loci (QTL) while introducing these traits into a commercially viable genetic background. I genotyped the LA1141 × OH8245 BC2S3 generation with single nucleotide polymorphisms, created a linkage map, and conducted composite interval mapping. Anthocyanins were identified as causal pigments, and QTL analysis revealed genetic regions that explained as much as 35% of the variation in color. These analyses led to the identification of candidate genes. Subsequent sequence and phylogenetic analyses supported a conservation of mechanism leading to purple fruit, while identifying novel alleles at the Anthocyanin fruit, atroviolacium, and uniform ripening l (open full item for complete abstract)

Committee: David Fancis PhD (Advisor); Jessica Cooperstone PhD (Committee Member); Mathew Kleinhenz PhD (Committee Member); Chieri Kubota PhD (Committee Member); Christine Spunrger PhD (Committee Member) Subjects: Horticulture; Plant Biology; Plant Sciences

Master of Science in Botany, Miami University, 2021, Botany

Abiotic stress is a challenge for crop improvement programs, especially for crops with a large amount of morphological variation such as Brassica rapa. Oil seed and leafy varieties of B. rapa differ in several ways, possibly representing trade-offs in resource allocation. In turn, different responses to resource allocation problems provide an opportunity to study aspects of genetic architecture such as epistasis. For the present thesis, I investigate complications in genotype-phenotype relationships with the aim of understanding abiotic stress responses. Towards this end, I conducted two experiments with a mapping population of B. rapa watered with either tap or salt water and measured several traits related to resource allocation. The first experiment revealed trade-offs between reproductive fitness and vegetative growth. I also found several Quantitative Trait Loci (QTL) and epistatic interactions associated with these traits. For the second experiment, I developed and tested a low-cost and scalable high-throughput phenotyping (HTP) system for automatically quantifying plant traits. Using RGB cameras, this HTP system reproduced treatment differences and developmental trends at a higher temporal density compared to manually acquired images. In future work, this system could lower the cost of research on genotype-phenotype relationships and crop improvement programs.

Committee: Robert L. Baker (Advisor); Richard Moore (Committee Member); Meixia Zhao (Committee Member) Subjects: Botany

Master of Science, The Ohio State University, 2020, Horticulture and Crop Science

In recent years, the North American region has seen increased usage of grafted vegetable transplants to reduce soil-borne disease incidence, increase tolerance to abiotic stress, enhance fruit quality, and increase yields over conventional nongrafted transplants. Grafting itself is a unique agrotechnology that merges a vegetable crop (scion) with the root system of another plant (rootstock) to form one transplant that benefits from both traits. In North America, a recent survey showed nearly 60 million grafted transplants are produced annually for fruiting vegetable crops, including tomato, watermelon, cucumber, pepper, eggplant, and muskmelon. Due to the limited number of nurseries in North America, transplants are commonly shipped 3-5 d to distant producers and have reportedly experienced chilling stress during transportation that reduces transplant quality and may affect post-transplanting performance. However, few studies have explored the specific effects of transport-related chilling stress on seedling quality and post-transplanting development. Using watermelon (Citrullus lanatus), a highly chilling sensitive member of the Cucurbitacea family, we examined effects of acute chilling stress on seedlings quality and post-transplanting development. When grafted and nongrafted seedlings were exposed to 0 - 48 h of 3 °C chilling, we found that seedling quality and post-transplanting development were unaffected by chilling. However, when the chilling temperature was reduced to 1 °C, seedlings exhibited increased visual damage of seedlings with longer durations, decreased chlorophyll fluorescence (Fv/Fm), and increased delays in the number of days it took for plants to reach male and female flower anthesis after transplanting. Nongrafted plants had longer delays in days to flower anthesis than grafted plants, indicating that grafted plants may have been more resistant to chilling or had enhanced flower primordia development that reduced the effects of acute chilling. (open full item for complete abstract)

Committee: Chieri Kubota (Advisor); Joseph Scheerens (Committee Member); Matthew Kleinhenz (Committee Member) Subjects: Agriculture; Horticulture; Physiology; Plant Biology; Plant Sciences

Master of Science, The Ohio State University, 2013, Horticulture and Crop Science

Grafting is a technique that has been used for fruit trees and vine crops for thousand years. Grafting to rootstocks is becoming popular in annual vegetable production to control soil-borne diseases, replace fumigation, increase yield, increase tolerance to abiotic stress, and impart vigor. Previous research indicates that inconsistent seed quality and lack of information about rootstock-scion compatibility affect the efficiency of grafting, raises cost, and inhibits adoption of the technology. The goals of this research were to address limitations in seed quality and graft efficiency. The specific objectives were: a) evaluate genetic and environmental factors affecting quality of seed in hybrids derived from interspecific crosses, b) improve grafting success through use of adhesives, and c) determine the genetic basis of graft failure between rootstock and scion. Tomato is a model for grafting annual vegetables due to the importance of the crop and the extensive genetic resources available. To assess the potential to select for improved seed quality, experimental rootstocks were developed through pollination of cultivated (Solanum lycopersicum L.) parental lines as female parents and 11 accessions of wild species as male parents. Seed quality was evaluated based on seed size (weight) and total germinability for each hybrid produced. Maternal effects and environment determined fruit set. Specific genotype combinations and environment determined seed yield. Seed size was mainly affected by genetic components, while seed germination was affected by both genetics and environmental factors. Seed size can be used as selection criterion in breeding program for early selection of rootstock seed quality. To improve graft success, nine different tomato rootstocks were grafted using the traditional tube method of grafting and using adhesives. Despite wide variation across rootstock genotypes and grafting environment, grafting using adhesives resulted in higher grafting suc (open full item for complete abstract)

Committee: David Francis M. Dr. (Advisor); Pablo Jourdan Dr. (Committee Member); Matthew Kleinhenz Dr. (Committee Member) Subjects: Agriculture; Agronomy; Horticulture; Plant Sciences

Doctor of Philosophy, Miami University, 2011, Chemistry and Biochemistry

Although the glyoxalase system was discovered more than seven decades ago, its specific functional roles are still unclear. It is believed that the major role for this system is the chemical detoxification of methylglyoxal. However, the identification of isoforms that are non-catalytic with methylglyoxal and S-lactoylglutathione, a known substrate for the enzyme, has suggested that it may play additional roles. Also the observation of increased glyoxalase expression during stress conditions and diseased state, as well as the ability to introduce stress tolerance in plants by the over-expression of glyoxalase enzymes indicates that the system may be responsible for more than just methylglyoxal detoxification. The fact that the glyoxalase system is present across a range of species, and is expressed in almost all tissues highlights the significance of this system, and why it is an important topic to study. It is with this larger question that the research described herein was conducted. Specifically, the questions that this dissertation addresses are - what are the likely roles of two glyoxalase II-like enzymes (GLX2-1 and ETHE1) in Arabidopsis thaliana? To address this question we have used genetic, cellular, transcriptomic, and metabolomic tools to observe changes in the model plant Arabidopsis when expression levels of these genes are altered. The results of the study establish that GLX2-1 has a role in stress response in Arabidopsis thaliana, and that the absence of GLX2-1 increases the sensitivity of plants to stresses like anoxia (lack of oxygen) and high salt conditions. In case of ETHE1, our results suggest that perturbation of this gene causes pleiotropic effects on plant growth and survival, and possibly due to alterations in mitochondrial function.

Committee: Christopher A. Makaroff Dr. (Advisor); Michael W. Crowder Dr. (Committee Chair); Ann E. Hagerman Dr. (Committee Member); Carole Dabney Smith Dr. (Committee Member); Qingshun Quinn Li Dr. (Committee Member) Subjects: Biochemistry