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Increasing Productivity And Biodiversity Of Tall Fescue Swards By Intercropping Cool And Warm-Season Forage Species, Michael Dereck Corbin

Doctoral Dissertations

Mixed pastures are known to produce greater biomass yields and higher nutritive value than monocultures. Intercropping biologically N fixating legumes, along with the use of intercropping warm-season annual grasses, such as crabgrass [Digitaria ciliaris Retz.], provides the potential to aid tall fescue [Schedonorus arundinaceus (Schreb.) Dumort.] productivity. To determine the benefits of intercropping species into tall fescue forage systems in the Southeastern U.S., two studies were developed. The first study consisted of 9 tall fescue paddocks, in which 3 paddocks contained red clover (Trifolium pratense L. [TRC]) mixed with tall fescue, 3 paddocks contained sunn …

Corn (Zea Mays L.) Production In Living Mulch Systems, Grazing Potential, And Economic Viability, Marcia Peireira Quinby

Doctoral Dissertations

Living mulch (LM) is a practice in which forages are grown simultaneously with the main crop, serving as a living cover throughout the growing season. The LM systems were developed to alleviate concerns of soil depletion and finding ways to reduce tillage negative effects on soil productivity. In addition, when legumes are use can decrease the reliance on N fertilizer. The use of corn in LM have been previously studied due to the crop being a large commodity in the U.S.; In addition, the ability to graze the LM after corn production can increase the land use efficiency. To determine …

Poa Annua: An Annual Species?, Devon E. Carroll

Doctoral Dissertations

Poa annua L. is ranked the most troublesome turfgrass weed but can also be a highly desirable turfgrass species. As the Latin name annua implies, the species is thought to persist via an annual life cycle; yet there are many reports in literature of P. annua persisting perennially. Considering that P. annua senescence patterns do not align with other true annual species such as Triticum spp. and Zea mays L., we hypothesized that P. annua presents itself similarly to other perennial, cool-season, turfgrass species that are subject to a confluence of environmental factors in summer that can cause mortality. …

Impacts Of Soil Management On Microbial Assemblages Involved In Nitrogen Transformations In Agroecosystems In Tennessee, Usa, Jialin Hu

Doctoral Dissertations

Nutrient reduction, particularly with respect to nitrogen (N) losses, is an important goal for sustainably managed agroecosystems. Soil N-cycling microbial populations that modulate these processes are affected by agricultural management regimes. This research focused on the controls and dynamics of the major N-cycling microbial populations in high-input cotton field under agricultural management regimes and low-input native C₄ forage grass systems under pasture management practices to determine the effects of management regimes on in situ seasonal dynamics of the functional microbes responsible for N fixation, nitrification, and denitrification processes. Molecular microbial ecology methods were combined with soil physicochemical properties and …

Characterization And Management Of Glyphosate-Resistant Junglerice, Clay M. Perkins

Doctoral Dissertations

Junglerice has become a major weed in Tennessee and across the mid-south. Glyphosate resistance and dicamba antagonism has resulted in the reported control failures and rise in prevalence. Junglerice was the most prevalent weed escape in cotton and soybean fields across Tennessee from 2018 to 2020. In all, 13% of the junglerice accessions could no longer be effectively controlled with glyphosate. Due to poor in-crop control, it has been recommended to start clean when trying to control junglerice and other grasses. Therefore, research was conducted to determine the best burndown methods utilizing dicamba, glufosinate, or paraquat. A sequential application of …

Identification Of Molecular Mechanisms Of Resistance To Transgenic Maize Producing The Cry1fa Protein In Different Spodoptera Frugiperda Populations, Rahul Banerjee

Doctoral Dissertations

The use of transgenic maize event TC1507 producing the Cry1Fa insecticidal protein from the bacterium Bacillus thuringiensis has been very useful to control the target lepidopteran insect pest Spodoptera frugiperda. The extensive use of this transgenic maize event resulted in high selection pressure for development of Cry1Fa resistance in field insects in multiple locations, including Brazil, Puerto Rico and the southeastern USA. Resistance developed in Puerto Rico was characterized in the 456LS3 strain originated from that island as monogenic, autosomal recessive and associated with reduced expression of a membrane bound alkaline phosphatase (SfmALP2). Currently, we focused on identifying the …

Modification Of Carbohydrate Active Enzymes In Switchgrass (Panicum Virgatum L.) To Improve Saccharification And Biomass Yields For Biofuels, Jonathan Duran Willis

Doctoral Dissertations

The natural recalcitrance of plant cell walls is a major commercial hurdle for plant biomass to be converted into a viable energy source as alternative to fossil fuels. To circumvent this hurdle manipulation of carbohydrate enzymes active in the cellulose and hemicellulose portions of the plant cell wall can be utilized to improve feedstocks. Production of cellulolytic enzymes by plants have been evaluated for reducing the cost associated with lignocellulosic biofuels. Plants have successfully served as bioreactors producing bacterial and fungal glycosyl hydrolases, which have altered plant growth to improve saccharification. A bioprospecting opportunity lies with the utilization of insect …

Salmonella In Low Water Activity Foods: Physiological, Genetic Modification And Control Methods, Wei Chen

Doctoral Dissertations

The objective of this study was to evaluate the expression of fatty acid associated genes (fabA, fabD and cfa) of five serovars of Salmonella exposed to sugar over a 14-day period. Changes in the fatty acid composition of Salmonella Tennessee in glycerol solutions of different water activity (a_w) (1.0-0.6) and the relationship between survival and fatty acid modification (as altered by exogenously supplied fatty acids) at a_w 1.0-0.6 were also determined. Furthermore, the antimicrobial activities of carvacrol, cinnamaldehyde, and lauric arginate (LAE) alone or in combination against Salmonella Tennessee in a laboratory model of …

Characterization Of The Role Of Alpha-Arylphorin In The Heliothis Virescens Midgut Response To Cry1ac Toxin From Bacillus Thuringiensis, Jerreme Jamael Jackson

Doctoral Dissertations

Homeostasis of the intestinal epithelium in Heliothis virescens is mediated by the proliferation and differentiation of multipotent intestinal stem cells (ISCs) that lie adjacent to the basal lamina. In response to extrinsic and intrinsic signals, ISC proliferation and differentiation promotes epithelial growth and regeneration following the loss of integrity. We tested the in vivo effects of the ISC mitogen, a [alpha]-arylphorin, on ISC proliferation and the morphological changes of the midgut during larval development. Additionally, we examined how these changes affected the intestinal epithelium response to Cry1Ac toxin from Bacillus thuringiensis. Histological and in vitro evidence supported two distinct …

Identification And Confirmation Of Quantitative Trait Loci For Protein Concentration And Improved Amino Acid Composition In Glycine Max, Jeneen Samantha Abrams

Doctoral Dissertations

The demand for poultry and swine production has grown continually as the world population increases. There will be an estimated 8 billion people to feed in the world by 2025. Soybean meal is the most important plant protein ingredient for poultry and swine feedstock. Globally, the US produces 32% of the world’s soybean. Although soymeal is nearly a complete plant protein, it is highly supplemented with sulfur-containing amino acids such as cysteine and methionine. The objectives of this project were to utilize molecular markers known as single nucleotide polymorphisms (SNPs) to identify genomic regions associated with protein concentration and amino …

World Wide Diversity Of Phytophthora Capsici, Dylan B. Storey

Doctoral Dissertations

The plant pathogen Phytophthora capsici is a genetically diverse organism that is a global problem. It effects many crops across the Solanacea, Cucurbitacea, andLeguminosea. As a result of the large diversity between individuals (and by extension populations) it has been previously near impossible to make meaningful comparisons between individuals of geographically distinct locations. Here we present the results of applying Next Generation Sequencing (NGS) technologies to a representative panel of isolates. This information and data is further used to demonstrate how this diversity has a functionally relevent effect on a class of proteins responsible for the infectious process. We …

Characterization Of Field Evolved Resistance To Transgenic Cry1fa Maize In Spodoptera Frugiperda (J. E. Smith), Siva Rama Krishna Jakka

Doctoral Dissertations

Transgenic Bt crops expressing Cry and Vip toxins from Bacillus thuringiensis (Bt) have been increasingly planted to manage insect pest damage on agricultural crops. The high adoption of Bt-based insecticidal technologies suggests an increase selection pressure for the evolution of resistance in insect populations. So far, nine insect species have developed field evolved resistance to Bt crops, yet the mechanisms involved in field evolved resistance are unknown. In the present study, the resistance mechanism in field evolved resistance to maize producing Cry1Fa in Spodoptera frugiperda collected in fields from Puerto Rico was characterized. High levels of resistance to …

Effects Of Leaflet Orientation And Root Morphology On Physiological Traits And Yield In Soybeans., Richard Dewayne Johnson

Doctoral Dissertations

Drought is the most important abiotic stress adversely affecting soybean (Glycine max (L.) Merr.) yield. Leaflet orientation has been shown to reduce leaflet temperatures and transpiration while root morphology has been related to slower wilting phenotypes. The objective of this study was to investigate effects of leaflet orientation and rooting morphology on whole plant transpiration, yield, water use efficiency, and other physiological traits in soybeans using grafting techniques, population lines, near-isogenic lines, and restrained leaf canopy experiments. Experiments were conducted in Knoxville, TN with additional yield trial plots at Springfield, Spring Hill, and Milan, TN. Data were collected on …

Giant Ragweed (Ambrosia Trifida L.) Biology, Competition, And Control In Cotton (Gossypium Hirsutum L.), Kelly Anna Barnett

Doctoral Dissertations

The objectives of this research were to evaluate control options and investigate the biology and competitiveness of glyphosate-resistant (GR) giant ragweed in cotton. Our results determined that glufosinate followed by glufosinate, glufosinate plus pyrithiobac, and glufosinate plus fluometuron at 0.56 or 1.12 kg ai ha^-1 resulted in the highest level of visual control and the highest yield. However, glufosinate followed by glufosinate was the only treatment that resulted in the highest yield and > 90% control of GR giant ragweed.

The development of glufosinate-tolerant, 2,4-D tolerant, and dicamba-tolerant crops may provide growers with new opportunities for difficult-to-control weeds such as …

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, …

Measuring Single Nucleotide Polymorphism In The Vegetable Pathogen Phytophthora Capsici, Daniel Jara Gobena

Doctoral Dissertations

Phytophthora capsici is a eukaryotic plant pathogen that causes root, fruit, and foliar disease on a variety of important vegetables including pepper, tomato, eggplant, snap and lima beans, and essentially all cucurbits. At some locations, populations utilize sexual and asexual reproduction, whereas at others, populations appear to be entirely asexual. The differing population structure has important implications for developing control strategies. Our objective was to develop SNP markers to characterize natural populations and laboratory crosses. In chapter two, a novel technique to assay SNP genotypes based on high-resolution DNA melting analysis is presented. In chapter three, the genetic diversity for …

Comparing The Midgut Regenerative Responses In Bacillus Thuringiensis-Susceptible And Resistant Heliothis Virescens Larvae, Anais Severiana Castagnola

Doctoral Dissertations

The crystal (Cry) toxins from Bacillus thuringiensis (Bt) display high specificity and toxicity against relevant insect pests and the use of Bt-based products continues to contribute to insect pest management. To protect this investment, further its potential, and investigate possible unintended effects, various research questions have been proposed. One issue related to Bt usage is the evolution of pest resistance to Bt toxins. The midgut epithelium is targeted by Cry toxins killing enterocytes, facilitating invasion of the hemocoel, leading to septicemia and mortality. While resistance may emerge from alterations to these steps, most research efforts have been focused on reduced …

Production And Roles Of Volatile Secondary Metabolites In Interactions Of The Host Plant Tomato (Solanum Lycopersicum L.) With Other Organisms At Multi-Trophic Levels., Gitika Shrivastava

Doctoral Dissertations

Tomato (Solanum lycopersicum L.) produces an array of volatile secondary metabolites that act as constitutive and induced defenses against a variety of insect pests and diseases. We studied the effect of beneficial microorganisms, an arbuscular mycorrhiza fungus (AM), Glomus intraradices, an entomopathogenic fungus (Bb), Beauveria bassiana and a combination of both (AM+Bb), as well as, pests, such as rootknot nematode (RKN) (Meloidogyne incognita) and beet armyworm (BAW) (Spodoptera exiguae H.) on the production of volatile compounds in the leaves and roots of tomato. Benzyl alcohol, 3-hexenoic acid, total other compounds and β-myrcene were significantly increased ( …

The Development Of Smallholder Tea Production In Tanzania: An Economic Analysis Of Factors Influencing Green Leaf Tea Output, Joseph Tarmo Nagu

Doctoral Dissertations

This study focused on smallholder tea production as one strategy for Tanzanian economic development. The central research question was the economic evaluation of the potential of this strategy for increasing peasant farmer income streams in an economy comprised of mostly subsistence farming.

Two objectives were: (1) the assessment of the extent to which selected production factors explain the variability in the annual output of green tea leaf (output) and (2) the estimation of the physical resource productivities and the computation of marginal value products (MVP's) of selected resources for a sample 150 smallholder tea farms in Njombe, Tanzania to determine …

An Investigation Of Some Of The Environmental And Edaphic Factors Effecting The Detoxification And Subsequent Degradation Of An Herbicide, Butachlor, Douglas D. Baird

Doctoral Dissertations

The influence of specific edaphic environmental factors on the detoxication and subsequent degradation of N-Butoxymethyl-2-chloro-2', 6' diethylacetanilide (butachlor) was evaluated under greenhouse and growth chamber conditions. Detoxication of butachlor, as measured by bioassay with barnyardgrass, was significantly enhanced by increasing temperatures to 32 C, making the soil alkaline, flooding, introducing relatively high levels of organic matter and by allowing exposure of more than four weeks. Total degradation of butachlor to C0₂ was enhanced also by high temperatures and length of exposure but was inhibited to a certain extent by flooding. Soil produced metabolites, of which three were soluble in …