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

Doctor of Philosophy, The Ohio State University, 2018, Plant Pathology

Salmonellosis cases caused by Salmonella enterica through pre-harvest contamination of fresh produce represent a risk to human health worldwide; however, little is known about the interactions between Salmonella, phytopathogens, environment, and the plant host contributing to this food safety issue. Furthermore, the control of Salmonella from “farm to fork” is challenging due to the development of resistance mechanisms towards current control methods and restrictions on use of antimicrobials imposed by regulatory agencies. We investigated the effects of specific environmental conditions on the persistence and dissemination of Salmonella enterica subsp. enterica serotype Typhimurium (S. Typhimurium) following artificial contamination of `Tiny Tim' tomato plants. We found that higher temperatures (30°C day/25°C night) reduced the persistence of S. Typhimurium in the phyllosphere compared to lower temperatures (20°C day/15°C night) when plants were sprayed on the leaves with a S. Typhimurium -contaminated solution. Wounding cotyledons with contaminated tools increased S. Typhimurium persistence and internalization in planta compared to spray inoculation. Low relative humidity enhanced the dissemination of Salmonella into non-inoculated plant tissues. S. Typhimurium was detected in the root systems for at least 98 days-post inoculation. Further, we showed that splice-grafting (`Celebrity' with 'MaxiFort') is a major risk for the internalization and long-term survival of S. Typhimurium inside the tomato plant. S. Typhimurium was detected in the root system for over 137 days if at least 5 x 10^3 colony-forming units were introduced during grafting. The survival of S. Typhimurium in tomato foliage was also affected by the presence of phytopathogens, the genotype of S. Typhimurium and tomato variety used. We found that rfbV, involved in O antigen synthesis, might be essential for S. Typhimurium persistence in inoculated tomato plants and especially in `Tiny Tim' plants (open full item for complete abstract)

Committee: Gireesh Rajashekara (Advisor); Sally Miller (Advisor); Laurence Madden (Committee Member); Christopher Taylor (Committee Member); Corey Nislow (Committee Member) Subjects: Agriculture; Bioinformatics; Biology; Environmental Health; Molecular Biology; Plant Pathology; Public Health

Doctor of Philosophy, The Ohio State University, 2016, Horticulture and Crop Science

Seedling development is a period of dynamic change within the overall vegetable plant and crop development period. For example, leaf area, stem length, and above-ground biomass can increase several fold within 1-3 weeks of emergence, possibly signaling high rates of carbon fixation on a per gram fresh weight basis and prescribed patterns of primary growth. Still, while general patterns of seedling development are familiar and the influence of individual major environmental factors on it are well chronicled, a reliable, accessible, and highly repeatable approach to describe the efficiency with which seedlings convert growth factors into biomass and partition it is unavailable. We hypothesized that plant and environmental data could be integrated into a single “seedling vigor” value allowing for more direct and consistent comparisons of seedling growth within and across experiments. We tested this hypothesis in a greenhouse experiment involving the simultaneous tracking of seven parameters of seedling growth (above-ground biomass and growth pattern) in twenty-three commercial tomato varieties and four environmental variables through 18 d after seeding. A formula created for the test used the plant and environmental data in calculating seedling vigor values and the experiment was repeated twice over a four-month period in the spring. Minimum and maximum seedling vigor values differed 79- to 575-fold among cultivars in runs 1 and 2, respectively, although relative variety vigor values were generally consistent between runs. These results demonstrate: 1) that varieties differ in their primary growth capacities under identical growing conditions and 2) that calculations of vigor like the one demonstrated here can reliably differentiate these capacities and help standardize reports including them. Normal seedling development, perhaps especially root-shoot communication and root and shoot level (carbon) partitioning, is severely disrupted in the process of grafting. In f (open full item for complete abstract)

Committee: Matt Kleinhenz (Advisor) Subjects: Horticulture

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