Life Sciences Commons^™

Characterization Of Lignin Structural Variability And The Associated Application In Genome Wide Association Studies, Nathan D. Bryant

Doctoral Dissertations

Poplar (Populus sp.) is a promising biofuel feedstock due to advantageous features such as fast growth, the ability to grow on marginal land, and relatively low lignin content. However, there is tremendous variability associated with the composition of biomass. Understanding this variability, especially in lignin, is crucial to developing and implementing financially viable, integrated biorefineries. Although lignin is typically described as being comprised of three primary monolignols (syringyl, guaiacyl, p-hydroxyphenyl), it is a highly irregular biopolymer that can incorporate non-canonical monolignols. It is also connected by a variety of interunit linkages, adding to its complexity. Secondary cell wall …

Improved And Sustainable Management Of Economically Important Plant-Parasitic Nematodes Of Field Crops And Fungal Diseases Of Soybean And Hemp In Tennessee, Rufus J. Akinrinlola

Doctoral Dissertations

Nematodes and diseases can limit field crops and hemp production in Tennessee. Therefore, seven research objectives were undertaken to improve the management of the crops: First, the prevalence and density of plant-parasitic nematode populations were evaluated across many field crop acreages in Tennessee through a survey from 2018 through 2020. Second, the virulence phenotypes of soybean cyst nematode (SCN), (Heterodera glycines [HG]), populations were assessed in Tennessee fields using the HG types test. Third, the impact of the virulent SCN HG type 1.2.5.7 on soybean nitrogen fixation activity and growth was evaluated on different soybean genotypes in the greenhouse. …

Multi-Omic Systems Biological Analysis Of Host-Microbe Interactions, Piet Jones

Doctoral Dissertations

Systems biology offers the opportunity to understand the complex mechanisms of various biological phenomena. The wealth of data that is produced, at an increasing rate, provides the potential to meet this opportunity. Here we take an applied approach to integrate multiple omic level data sources in order to generate biologically relevant hypotheses. We apply a novel analysis pipeline to model both, in concert, the microbial and transcriptomic signature from COVID-19 positive patients. We show patients may suffer from an increased microbial burden, with an increased pathogen potential. Gene expression evidence further shows patients may exhibit a compromised barrier immunity, owing …

Fungicide Sensitivity Screening Of Corynespora Cassiicola In Us Soybean And Cotton, Tyler Miles Smith

Doctoral Dissertations

Target spot, caused by the fungus Corynespora cassiicola, is a foliar disease of cotton and soybean. Target spot has become a disease of concern in soybean and cotton production systems. Data for fungicide sensitivity and understanding potential impact on yield is lacking for C. cassiicola. Fungicide resistance is also a concern in C. cassiicola with the increase in resistant pathogens in soybean. With the lack of knowledge about baseline fungicide sensitivity and the concern of fungicide resistance the objectives of this study were: (i) to evaluate fungicide products and mixes in small plot soybean and cotton trials, (ii) …

Genetic Analysis Of Field Populations Of The Plant Pathogens Cercospora Sojina, Corynespora Cassiicola And Phytophthora Colocasiae, Sandesh Kumar Shrestha

Doctoral Dissertations

Genetic markers and whole genome sequencing (WGS) were used to study the disease dynamics and population structure for three important plant pathogens; Cercospora sojina (frogeye leaf spot of soybean), Corynespora cassiicola (target spot of soybean, cotton and many other crops) and Phytophthora colocasiae (taro leaf blight). For each pathogen, genome sequencing was used to guide the development of single nucleotide polymorphism (SNP) markers and both were used to investigate diversity in field populations. Investigation of C. sojina in Tennessee included comparisons of extant populations and historical isolates, revealing a dominant, potentially long-lived, clonal lineage. Characterization of QoI fungicide resistance indicates …

Pathogenesis, Virulence And Population Genetics Of Puccinia Emaculata, The Causal Agent Of Switchgrass Rust, Qunkang Cheng

Doctoral Dissertations

The infection process of Puccinia emaculata on Panicum virgatum leaves was studied histologically. Appressoria were formed approximately 10 hr after inoculation and penetrations were observed over stomatal openings. Substomatal vesicles developed 3 days after inoculation (DAI) and at 5 DAI, both haustorial mother cells and haustoria were observed. At 11 DAI, uredinia were developing, but urediniospores were immature. Until 14 DAI, matured uredinia ruptured host epidermis and urediniospores were released for secondary infection. This clearly studied infection process will help understand resistance mechanisms of a resistant cultivar in future research.

Twelve agronomic and ornamental switchgrass cultivars were inoculated with 40 …

Antibacterial Activity And Chemical Characterization Of Resin From Sciadopitys Verticillata (Thunb.) Siebold And Zuccarini, David Ira Yates

Doctoral Dissertations

Sciadopitys verticillata produces white viscous resin that is unique among the conifers. This research investigated effects of resin on bacteria from different ecological niches and the chemical composition of the resin. Each bacterial species was evaluated separately for response to winter- and summer-collected resins. Exposure to winter-collected resin reduced numbers of colonies of Bacillus cereus, Erwinia amylovora, Agrobacterium tumefaciens, and Escherichia coli and increased numbers of Xanthomonascampestris, Pseudomonas fluorescens, and Pseudomonas syringae. Summer-collected resin affectedpopulation growth of two bacterial species; population counts of E. amylovora decreased and those of P. fluorescens increased. Selected strains of …

Improved Fungicidal Control Of Large Patch Through Optimal Use Of Surfactants And Spray Rate Volume, Jesse J. Benelli

Doctoral Dissertations

Large patch (Rhizoctonia solani AG 2-2LP) epidemics cause significant damage to Japanese lawngrass (JLG; Zoysia japonica) in the transition zone. Large patch primarily affects the stems and sheaths of JLG and is difficult to control using traditional fungicide sprays. Field and growth chamber experiments were conducted during 2015-2016 in TN and GA to evaluate methods to enhance fungicidal control of large patch in JLG landscapes. The 1^st experiment evaluated the most critical application target site that resulted in the greatest amount large patch control. In this experiment, four fungicides (azoxystrobin, flutolanil, tebuconazole, and chlorothalonil) were dispensed as …

Anaerobic Soil Disinfestation: Meta-Analysis And Optimization Of Amendment Carbon Rate And C:N Ratio To Control Key Plant Pathogens And Weeds, Utsala Shrestha

Doctoral Dissertations

Anaerobic soil disinfestation (ASD) is an environmentally friendly and cost effective pre-plant soil treatment technique that allows effective control of soilborne pests by creating anaerobic conditions, particularly for specialty and organic crop production under diverse environmental conditions. In spite of being a proven technique, ASD has to be optimized to fit into local production systems with specific pathogen pressure using locally available amendments for successful implementation on a commercial scale. Our meta-analysis study on soilborne pathogens, plant parasitic nematodes, and weeds validated that ASD is an effective approach to control various soilborne pathogens. This study aims to optimize the carbon …

Calmodulin-Like Protein 38: A Component Of Ribonucleoprotein Particles During Hypoxic Stress Responses In Arabidopsis, Ansul Lokdarshi

Doctoral Dissertations

Waterlogging stress leads to a crisis in energy metabolism and the accumulation of toxic metabolites due to the hypoxic and/or anoxic environment associated with this condition. To respond and adapt to this situation, higher plants employ an integrated genetic program that leads to the induction of anaerobic response polypeptide genes that encode metabolic and signaling proteins involved in altering metabolic flow and other adaptive responses. The study presented here shows that the Arabidopsis thaliana calmodulin-like protein CML38 is calcium sensor protein that serves as a member of the core anaerobic response gene family and is involved in modulating the survival …

Efficacy Of Biopesticides For Organic Management Of Cucumber Beetles, Mary A. Rogers

Doctoral Dissertations

Organic growers are limited in crop protection techniques for cucumber beetle management. Spotted (Diabrotica undecimpunctata howardi) and striped (Acalymma vitatta) cucumber beetles and are significant pests of cucurbits in the U.S. Feeding results in aesthetic damage and reduction in marketable yields as well as transmission of bacterial wilt that can result in plant mortality. Biopesticides are products formulated from naturally occurring organisms such as fungi and bacteria that are pathogenic or toxic to insect pests. Advantages to these products are that they have low environmental risk, low risk to non-target organisms including mammals and beneficial insects, …

Evaluation Of Genetic Diversity Of Flowering Dogwood (Cornus Florida L.) In The Eastern United States Using Microsatellites., Denita Hadziabdic

Doctoral Dissertations

Flowering dogwood (Cornus florida L.) populations have experienced severe declines caused by dogwood anthracnose in the past three decades. Mortality has ranged from 48 to 98%, raising the concern that genetic diversity of this native tree has been reduced significantly. Microsatellite data were used to evaluate the level and distribution of genetic variation throughout much of the native range of the tree. In the first conducted study, we found that genetic variation in areas affected by anthracnose was as high as or higher than areas without die-offs. We found evidence of four widespread, spatially contiguous genetic clusters. However, there was …