Plant Sciences Commons^™

Assessing Endophyte Frequency Distributions And The Effect Of Epichloë Brachyelytri In The Chemotypic And Genotypic Diversity Of Brachyelytrum Erectum, Rachel Ann Sneed

Theses and Dissertations--Plant Pathology

Seed-transmissible epichloid fungal endophytes are best known for their roles as defensive mutualists in cool-season grasses. Historically, the discovery of fungal endophytes was driven by investigations of plant toxicity to livestock, followed by extensive study of their alkaloids and protection against insects and nematodes. Epichloae can produce four classes of alkaloids: ergot alkaloids, lolines (saturated aminopyrrolizidines), indole–diterpenes, and peramine. It is increasingly evident that these hereditary symbionts have much more diverse chemical profiles both in individual populations and between them. To this end, differences in chemotypic profiles of these symbionts may translate to different evolutionary and environmental advantages across plant …

Exploring The Effects Of Environmental Factors On Rice Blast Disease, April Ellen Lamb

Theses and Dissertations--Plant Pathology

Rice blast disease, caused by the ascomycete fungus Magnaporthe oryzae, occurs in over 85 countries and results in an annual crop loss of 10-30%, a corresponding nutrient value of meals for 60 million people. As a result, it is listed as a critical plant disease by the United Nations. Understanding factors affecting disease severity is of critical concern for food security. M. oryzae has been used as a model system for studying effector-triggered immunity (ETI) by understanding that ETI is primarily a plant response. M. oryzae has been used as a model to study fungal pathogenicity, host specificity, genome …

An Improved Understanding Of Diplodia Ear Rot In Kentucky Corn, Nolan Ryan Anderson

Theses and Dissertations--Plant Pathology

Stenocarpella maydis and Stenocarpella macrospora are both causal agents of Diplodia ear rot (DER) of corn in the U.S. The current prevalence and distribution of each is unknown worldwide. Signs and symptoms of DER include white mold on and between kernels, bleached husks, and pycnidia visible in the cob pith. The term hidden Diplodia describes when no mycelia or bleached husk is present, but pycnidia are still visible inside the cob. This phenomenon is reported to be caused by late infections of Stenocarpella spp. New fungicide nozzle technology has been promoted to increase spray coverage in the lower canopy, which …

An Examination Of Organic Options In Tomato Systems And Their Use As Alternatives To Copper-Based Products, Erica Ann Fealko

Theses and Dissertations--Plant Pathology

Organic farming is an ever-increasing segment of tomato production. Currently, limited information is available which directly compares conventional to organic treatment programs for disease control in tomato production. Furthermore, many methods available rely on the use of copper products which may be contribute to high Cu levels in agricultural soils. In this study, the efficacies of current conventional and organic methods were compared. In addition, newer disease-control programs, with and without copper were examined, which potentially could reduce over-reliance on copper products.

Standard organic and conventional spray programs were conducted over a four year period targeting two pathogens, Alternaria tomatophila …

The Role Of Nitric Oxide In Inter- And Intra- Cellular Signaling In Plant Defense, Fan Xia

Theses and Dissertations--Plant Pathology

Plants have evolved a sophisticated immune system to defend themselves against pathogens. This immune response can be triggered in response to pathogen-associated molecular patterns (PAMP) or specialized effectors that are recognized by the plant resistance (R) proteins. The latter, commonly referred to as effector-triggered immunity (ETI), is well known to induce broad-spectrum resistance throughout the plants. This phenomenon known as systemic acquired resistance (SAR) is regulated by several chemical signals including salicylic acid (SA), and free radical nitric oxide (NO) and reactive oxygen species (ROS). These signals operate in two parallel branches with NO/ROS functioning downstream of pipecolic acid (Pip) …

Epidemiology And Management Of Frogeye Leaf Spot Of Soybean: Damage Thresholds, Efficacy And Profitability Of Foliar Fungicides, Jhonatan Paulo Barro

Theses and Dissertations--Plant Pathology

Frogeye leaf spot (FLS), caused by Cercospora sojina, is an economically important disease of soybean in many parts of the world where soybean is grown, including the United States. A meta-analytic approach was used to summarize a data set of 66 uniform field research trials conducted to evaluate fungicide efficacy against FLS on soybean. The dataset spanned 10 years (2012 to 2021) of experiments conducted across eight states in the U.S., including Alabama, Arkansas, Illinois, Iowa, Kentucky, Louisiana, Mississippi and Tennessee. First, the relationship between FLS severity and soybean yield was investigated. A significant negative slope obtained through random …

Characteristics Of Cercospora Nicotianae With Reduced Sensitvity To Azoxystrobin, William Barrett Barlow

Theses and Dissertations--Plant Pathology

Burley and dark tobacco production are important to agriculture in Kentucky, worth $145.1 and $94.4 million in 2020, respectively. The price received for a tobacco crop is influenced by leaf quality, determined by multiple characteristics including leaf damage. Frogeye leaf spot (FLS), caused by Cercospora nicotianae, has historically been a minor disease of tobacco. However, when FLS infections reach the upper canopy of tobacco, lesions are seen as damage that negatively influence leaf quality. Fungicides are regularly used to manage foliar diseases of tobacco, and the only systemic fungicide active ingredient labeled for tobacco is azoxystrobin. Azoxystrobin belongs to the …

Seeing Double With Cannabis: Heteroploid Populations In Bipolaris Gigantea, Causal Agent Of Bipolaris Leaf Spot, Desiree Szarka

Theses and Dissertations--Plant Pathology

Bipolaris leaf spot (BLS) disease emerged with the reintroduction of hemp as a crop in the United States following more than 60 years of prohibition. The causal agent was identified as Bipolaris gigantea (=Drechslera gigantea), a known minor pathogen of monocots which causes devastating disease on hemp. BLS has been confirmed throughout Kentucky and reported in 15 states. Morphology and growth characteristics of isolates from eight counties across Kentucky were similar with the exception of some isolates producing protoperithecial-like structures. Phylogenetic and whole genome analysis indicated that some isolates were haploid, containing a single allele at each gene …

The Roles Of The Actin Network And Co-Opted Host Factors In Tbsv Replication, Melissa Gabriela Molho Medina

Theses and Dissertations--Plant Pathology

Positive-stranded (+) RNA viruses are the largest family of viruses that infect plants, causing important economic losses in different crops. Tomato bushy stunt virus (TBSV), a small positive-stranded RNA virus, has emerged as a model virus to study virus-host interactions. TBSV encodes for only five proteins, therefore, to infect the host cell TBSV co-opts selected host components and subverts specific molecular pathways.

Firstly, I performed a proteomic screening using Arabidopsis proteins. I found that TBSV viral replication proteins interact with 88 host proteins, including the ubiquitin-conjugating enzyme 2 (Ubc2), fructose 1,6 biphosphate aldolase (Fba1), and several members of the Hps70 …

Wheat Disease Management With Fungicides: Qoi-Resistant Parastagonospora Nodorum And Zymoseptoria Tritici, Application Timing For Leaf Disease Management, And Sprayer Configurations For Fusarium Head Blight Management, Nathaniel Heubeck White

Theses and Dissertations--Plant Pathology

Disease management in winter wheat can be improved by a properly implemented foliar fungicide program. The fungicide, application time, and application system should be selected based on the host, pathogens present, risk of fungicide resistance, and time of disease onset. These factors vary among environments and require region-specific research to determine appropriate practices. Trials were conducted to evaluate different aspects of fungicide applications for managing Fusarium head blight (FHB), caused by Fusarium graminearum, and the Septoria tritici leaf blotch complex, caused by Zymoseptoria tritici and Parastagonospora nodorum. A survey of P. nodorum isolates from Kentucky and Illinois and …

Negative Regulatory Factors In Tombusvirus Replication: Known Proteins, Novel Roles, Paulina Alatriste González

Theses and Dissertations--Plant Pathology

Although host cells are a rather rich source for co-opted host factors, lipids and metabolites, positive stranded RNA viruses vastly rewire cellular pathways and remodel cellular membranes to support viral replication. To accomplish such major changes, these viruses depend on the availability of different host factors and the ability to readily assemble viral replication organelles (VROs). Genome-wide screens and proteomics approaches with Tomato Bushy Stunt Virus (TBSV) in a yeast model host indicated that tombusviruses rely on the cellular cytoskeleton to reorganize the cellular environment of their hosts. Using temperature-sensitive (ts) mutants of beta and gamma-tubulin proteins and pharmacological inhibitors, …

Virus-Induced Changes In Nuclear Proteins And Membranes In Nicotiana Benthamiana Cells, Caleb Mathias

Theses and Dissertations--Plant Pathology

Viruses rely on host proteins to complete their life cycles. This results in alterations to normal cell physiology to processes which benefit viral processes such as replication and movement to other cells. This may involve the relocalization of host proteins away from their original subcellular targets to sites which may benefit the virus, a process that is not as well understood as it relates to the nucleus. To identify nuclear proteins that may be involved in such processes, a library of random Nicotiana benthamiana cDNAs were expressed as GFP fusions in a transgenic marker lines expressing a histone 2B:RFP nuclear …

Characterizing The Roles Of Pipecolic Acid And Reactive Oxygen Species Metabolic Enzymes In Plant Systemic Immunity, Ruiying Liu

Theses and Dissertations--Plant Pathology

Systemic acquired resistance (SAR), initiated by a plant upon recognition of microbial effectors, involves the generation of mobile signals at the primary infection site, which translocate to and activate defense responses in distal tissues. Among the signals contributing to SAR include salicylic acid (SA), nitric oxide (NO), reactive oxygen species (ROS), glycerol-3-phosphate (G3P), and pipecolic acid (Pip). Our previous studies show there are two branches of SAR signaling pathways in Arabidopsis: one regulated by NO/ROS-G3P and the other by SA. Both NO/ROS-G3P and SA-mediated signaling branches function in parallel during SAR. To better understand the role of Pip in SAR …

Diversity And Cross-Infection Potential Of Colletotrichum On Apples And Small Fruits In Kentucky Mixed-Fruit Orchards, Madison Julia Eaton

Theses and Dissertations--Plant Pathology

Fungi in the genus Colletotrichum cause apple, blueberry, and strawberry fruit rots, which result in significant losses for Kentucky growers. Most orchards in Kentucky are agritourism-focused and grow multiple fruits in close proximity. These mixed-fruit orchards may facilitate Colletotrichum cross-infection, which has serious management implications. Small fruit and apple Colletotrichum isolates from Kentucky orchards were characterized by morphotype, phylogenetic species identification, cross-inoculation, genome sequencing, and telomere fingerprinting. The small fruit isolates grouped into seven morphotypes, representing two species complexes: C. acutatum and C. gloeosporioides. All blueberry isolates belonged to the species C. fioriniae, and the majority of strawberry …

Pathogenicity, Toxigenic Potential, And Genomics Of Fusarium Graminearum And F. Meridionale Causing Ear And Stalk Rot Of Maize, Franklin Jackson Machado

Theses and Dissertations--Plant Pathology

Gibberella ear (GER) and stalk rot (GSR) diseases of maize in Brazil are caused mainly by Fusarium meridionale, a species belonging to the Fusarium graminearum species complex (FGSC). Another species within this complex, F. graminearum sensu stricto (hereafter F. graminearum), is second in importance on maize, but is the most common species found causing Fusarium Head Blight disease of wheat in Brazil. The latter species is the predominant cause of GER and GSR in North America, where F. meridionale has not been found thus far. In this dissertation I undertook a comparative analysis of pathogenic, saprophytic, toxigenic and …

Strain-Specific Protein Interaction And Localization Of Two Strains Of Potato Yellow Dwarf Virus And Functional Domains Of Their Matrix Protein, Chanyong Jang

Theses and Dissertations--Plant Pathology

Potato yellow dwarf virus (PYDV) is the type species of the genus nucleorhabdovirus which is typified by its nucleotropic characters of the members. The virus accomplishes its replication and morphogenesis in the nuclei of infected cells. Two strains, Constricta strain (CYDV) and Sanguinolenta strain (SYDV) have been described at the level of vector-specificity. CYDV is vectored by Agallia constricta and SYDV is transmitted by Aceratagllia sanguinolenta. The full-length genome of CYDV was sequenced. The 12,792 nt antisense genome encodes seven open reading frames in the order of, nucleocapsid protein (N), unknown protein (X), phosphoprotein (P), movement protein (Y), matrix …

Evaluation Of Trichoderma Spp. As Biocontrol Agents For Soybean Diseases, Jonathan Vance Lacey

Theses and Dissertations--Plant Pathology

Fungi in the genus Trichoderma have been characterized as biocontrol agents of plant pathogens since the 1930s. The use of biologicals for disease management has increased in recent years, typically marketed as a safer alternative to chemical applications. However, biologicals often lack consistent control across varying environmental conditions. To overcome the loss in efficacy due to environmental conditions, biologicals can be combined with common fungicide seed-treatments to provide improved control. Additionally, the presence of a biological organism could slow the development of a pathogen population. Greenhouse trials were conducted to determine the baseline root colonization of three Trichoderma spp. used …

Genetic Diversity Of Colletotrichum Sublineola On Sweet Sorghum And Wild Sorghum Relatives In Kentucky And The Southeastern U.S., Katia Viana Xavier

Theses and Dissertations--Plant Pathology

Anthracnose, caused by the fungus Colletotrichum sublineola, is one of the most important diseases on sorghum (Sorghum bicolor) in the United States (U.S.) and worldwide. The production of sweet sorghum for feedstock has been increasing in the Southeastern U.S. (SE), and anthracnose has emerged as a significant production constraint. Anthracnose is also common on the ubiquitous wild sorghum relative, johnsongrass (Sorghum halepense). The degree to which the pathogen population on johnsongrass contributes to disease epidemics on cultivated sorghum (S. bicolor) in the SE is unknown. Genetic and pathological diversity was characterized among a …

Establishment Of Biotrophy By The Maize Anthracnose Pathogen Colletotrichum Graminicola: Use Of Bioinformatics And Transcriptomics To Address The Potential Roles Of Secretion, Stress Response, And Secreted Proteins, Ester Alvarenga Santos Buiate

Theses and Dissertations--Plant Pathology

Colletotrichum graminicola is a hemibiotrophic pathogen of maize that causes anthracnose leaf and stalk rot diseases. The pathogen penetrates the host and initially establishes an intracellular biotrophic infection, in which the hyphae are separated from the living host cell by a membrane that is elaborated by the host, apparently in response to pathogen signals. A nonpathogenic mutant (MT) of C. graminicola was generated that germinates and penetrates the host normally, but is incapable of establishing a normal biotrophic infection. The mutated gene is Cpr1, conserved in eukaryotes and predicted to encode a component of the signal peptidase complex. How …

Characterization Of Colletotrichum Species Causing Bitter Rot Of Apples In Kentucky Orchards, Misbakhul Munir

Theses and Dissertations--Plant Pathology

Multiple species of Colletotrichum can cause bitter rot disease of apple, but the identities and relative representation of the species causing the disease in Kentucky are unknown. A total of 475 Colletotrichum isolates were collected from diseased apples in 25 counties and characterized both morphologically and by using various molecular approaches. Four morphotypes corresponded to reported descriptions of bitter rot species. Morphotype 1, distinguished by the production of a pink color on potato dextrose agar (PDA), orange conidial masses, and fusiform spores, was consistent with C. acutatum. Morphotype 2, which produced gray or white mycelial colonies with orange conidial masses …

Evaluation Of Pcr-Based Methods For Rapid, Accurate Detection And Monitoring Of Verticillium Dahliae In Woody Hosts By Real-Time Polymerase Chain Reaction, Baker Diwan Getheeth Aljawasim

Theses and Dissertations--Plant Pathology

Verticillium wilt, caused by Verticillium dahliae Kleb, is one of the most economically important diseases of woody hosts such as ash (Fraxinus spp.), sugar maple (Acer saccharum), and redbud (Cercis canadensis). The causal agent has a broad host range, including not only woody hosts but also important vegetable and field crops, and it is distributed worldwide. Diagnosis of V. dahliae in infected woody hosts is often based on the occurrence of vascular discoloration and time-consuming isolation. However, not all woody hosts exhibit vascular discoloration symptoms, and not all vascular discoloration symptoms are due to infection …

Rna Sequence Determinants Of A Coupled Termination-Reinitiation Strategy For Translation Of Downstream Orf In Helminthosporium Victoriae Virus 190s And Other Victoriviruses (Family Totiviridae), Hua Li

Theses and Dissertations--Plant Pathology

Double-stranded RNA fungal virus Helminthosporium victoriae virus 190S (genus Victorivirus, family Totiviridae) contains two large open reading frames (ORFs) that overlap in the tetranucleotide AUGA. Translation of the downstream ORF, which encodes the RNA-dependent RNA polymerase (RdRp), was previously proposed to depend on ribosomal reinitiation following termination of the upstream ORF, which encodes the capsid protein. In this study, I provided evidence to confirm that coupled termination-reinitiation (stop-restart) is indeed used. A dual-fluorescence method was established to define the RNA sequence determinants for RdRp translation. Stop-restart depends on a 32-nt stretch of RNA sequence immediately upstream of the …

Key Roles Of Sub-Cellular Membranes And Co-Chaperone In Tombusvirus Replication, Kai Xu

Theses and Dissertations--Plant Pathology

Positive strand RNA viruses, inculding tombusviruses, are known to utilize cellular membranes to assemble their replicase complexes (VRCs). Two tombusviruses , Tomato bushy stunt virus (TBSV) and Carnation Italian ringspot virus (CIRV), replicate on different organellar membranes, peroxisomes or endoplasmic reticulum (ER) for TBSV and mitochodria outer membranes in case of CIRV. I showed that both TBSV and CIRV replicase proteins could assemble VRCs and replicate viral RNA on purified microsomes (ER) and mitochondria. Different efficiencies of assembly was shown determined by multiple domains on TBSV or CIRV replication proteins.

To study why VRC assembly could occur on an alternative …

Alternative Methods Of Control For Phytophthora Nicotianae Of Tobacco, Anna M. Holdcroft

Theses and Dissertations--Plant Pathology

Kentucky is the nation’s leading producer of burley tobacco and the crop’s most economically important disease is black shank, caused by Phytophthora nicotianae (Pn). Current management is effective, however, problems with expense and pathogen persistence are issues. Two alternative methods for control of Pn were examined: biofumigation and soil application of an organic, yeast fermentation‐derived product (Soil‐Set). Field studies in 2009 and 2010 found no effect on populations of fungi, disease severity of Pn, and yield between mustard‐ and wheat‐amended plots. Experiments in the greenhouse suggested that survival of Pn was impacted by biomass rather than biofumigation. Biofumigation is not …

Cellular And Molecular Aspects Of The Interaction Betwen Maize And The Anthracnose Pathogen Colletotrichum Graminicola, Maria F. Torres

Theses and Dissertations--Plant Pathology

Maize anthracnose, caused by the fungus Colletotrichum graminicola, is an economically important species contributing to major yield losses. C. graminicola is a hemibiotroph; initially it invades its host while it is alive, and then it switches to destructive necrotrophic growth and the host is killed. Establishment of compatible interactions by biotrophic pathogens is usually associated with suppression of host defenses and cell death, while necrotrophic pathogens typically secrete phytotoxic compounds and induce cell death. To understand the relationship of hemibiotrophy in C. graminicola to biotrophy and necrotrophy, I compared a compatible and an incompatible interaction, utilizing a non-pathogenic …

Overexpression/Silencing Of Selected Soybean Genes Alters Resistance To Pathogens, Mohamed H. El-Habbak

Theses and Dissertations--Plant Pathology

Plant diseases remain a major obstruction to meeting the world’s increased demand for soybean oil and protein. Reducing the losses caused by diseases in order to improve crop production is a high priority for agricultural research. The need for novel strategies for plant disease control cannot be overstated. In the present study, selected defense-related genes were silenced and/or overexpressed in soybean using a virus-based vector and the resultant plants were tested for their responses to pathogens. The first part of the study focused on Rps1k (Resistance to Phytophthora sojae) gene. The two conserved domains encoding ‘P-Loop NTPase’ and ‘PLN03210’ …

Molecular And Biochemical Characterization Of Oleate- And Glycerol-3-Phosphate-Regulated Signaling In Plants, Mihir Kumar Mandal

Theses and Dissertations--Plant Pathology

Oleic acid (18:1), a monounsaturated fatty acid (FA), is synthesized upon desaturation of stearic acid (18:0) and this reaction is catalyzed by the plastidal enzyme stearoyl-acyl carrier protein-desaturase (SACPD). A mutation in the SSI2/FAB2 encoded SACPD lowers 18:1 levels, which correlates with induction of various resistance (R) genes and increased resistance to pathogens. Genetic and molecular studies have identified several suppressors of ssi2 which restore altered defense signaling either by normalizing 18:1 levels or by affecting function(s) of a downstream component. Characterization of one such ssi2 suppressor mutant showed that it is required downstream of low 18:1-mediated constitutive …

Glycerolipids And The Plant Cuticle Contribute To Plant Immunity, Qing-Ming Gao

Theses and Dissertations--Plant Pathology

The conserved metabolites, oleic acid (18:1), a major monounsaturated fatty acid (FA), and glycerol-3-phosphate (G3P) are obligatory precursors of glycerolipid biosynthesis in plants. In Arabidopsis, the SSI2-encoded SACPD is the major isoform that contributes to 18:1 biosynthesis. Signaling induced upon reduction in oleic acid (18:1) levels not only upregulates salicylic acid (SA)-mediated responses but also inhibits jasmonic acid (JA)- inducible defenses. I examined the transcription profile of ssi2 plants and identified two transcription factors, WRKY50 and WRKY51. Although the ssi2 wrky50 and ssi2 wrky51 plants were constitutively upregulated in SA-derived signaling, they were restored in JAdependent defense signaling. Not only …

Glycerol-3-Phosphate Is A Novel Regulator Of Basal And Induced Defense Signaling In Plants, Bidisha Chanda

Theses and Dissertations--Plant Pathology

Plants use several strategies to defend themselves against microbial pathogens. These include basal resistance, which is induced in response to pathogen encoded effector proteins, and resistance (R) protein-mediated resistance that is activated upon direct or indirect recognition of pathogen encoded avirulence protein(s). The activation of Rmediated signaling is often associated with generation of a signal, which, upon its translocation to the distal uninfected parts, confers broad-spectrum immunity against related or unrelated pathogens. This phenomenon known as systemic acquired resistance (SAR) is one of the well-established forms of induced defense response. However, the molecular mechanism underlying SAR remains largely unknown. Induction …

Role Of The Sexual Cycle In Development Of Genotypic And Phenotypic Diversity In Gibberella Zeae, Sladana Bec

Theses and Dissertations--Plant Pathology

Gibberella zeae (anamorph Fusarium graminearum) is a homothallic ascomycete pathogen that is responsible for causing Fusarium head blight (FHB) of wheat and small grains. In addition to causing a reduction in yield, harvested grain is frequently contaminated with trichothecene mycotoxins that are harmful for human and animal health. Use of wheat varieties with resistance to FHB is an important strategy to lower its impact. In order to produce varieties with durable resistance, we must understand the origin and degree of genetic diversity present in the pathogen population. In my research, I focused my efforts on an investigation of the …