Plant Sciences Commons^™

Inheritance Of Virulence In The Root Rot Pathogen Phytophthora Sojae, Sirjana Devi Shrestha

Electronic Thesis and Dissertation Repository

The oomycete Phytophthora sojae causes stem and root rot of soybean plants. The interaction of pathogen avirulence (Avr) and host resistance (R)-genes determine the disease outcome. The Avr3a mRNA transcript level is variable among P. sojae strains and determines virulence towards the R-gene Rps3a. To study the inheritance of virulence, genetic crosses and self-fertilizations were performed. A cross between P. sojae strains ACR10 and P7076 causes transgenerational gene silencing of Avr3a allele, and this effect is meiotically stable up to the F₅ generation. However, test-crosses of F₁ (Avr3a^ACR10/Avr3a …

Identification Of Root-Knot Nematodes (Meloidogyne Spp.) Of Arkansas Using Molecular Diagnostics, Churamani Khanal

Graduate Theses and Dissertations

Root-knot nematodes (Meloidogyne spp.) are highly-adaptable, obligate plant parasites distributed worldwide. In addition, root-knot nematodes are an economically important genus of plant-parasitic nematodes. Meloidogyne incognita, M. arenaria, M. javanica, M. hapla and M. graminis have been reported from Arkansas during 1964 to 1994. Previous identifications were based primarily on morphological characters and host differentials. In this study, identification using molecular diagnostics methods was performed to identify Meloidogyne species present in Arkansas. A total of 106 soil and root samples from 36 of the 75 counties were collected and processed to obtain root-knot nematodes. Polymerase chain reaction (PCR) was performed …

Evaluation Of Medicago Truncatula Accessions For Triterpene Saponins And Their Potential Impacts On Plant Pests, Samantha Roberson

Graduate Theses and Dissertations

Plants have developed numerous ways to protect themselves from microbes and insects, including producing secondary metabolites that negatively impact an invading pathogen or pest. Saponins are specialized metabolites found in many plant species and may play a role in protecting the plant. Though saponins are found in many plant species, triterpene saponins are found primarily in dicotyledons, including legumes. Medicago truncatula is a model system for studying legume biology and some accessions accumulate high concentrations of saponins. Accessions of M. truncatula known to have differing levels of saponins in both foliar and root tissues were tested for their suitability as …

The Phenotypic Effects And Transcript Response Of Salt Stress, The Impact Of Viral Infection On Salt Stress Symptoms, And The Effect Of Salt Stress On Soybean Virus Vector Activity In Soybean Varieties That Vary In Chloride Uptake, Alma Glenn Laney

Graduate Theses and Dissertations

With the increase in saline soils worldwide, understanding the mechanisms for salt tolerance in plants is important to reduce yield loss due to salt stress. Soybean, Glycine max (L.) Merr., genotypes differ in chloride uptake with genotypes that take up chloride into foliar tissues tending to be salt-sensitive whereas those that partially exclude chloride from the leaves are more salt-tolerant. Transcriptional and physiological responses were measured in two soybean cultivars, Clark and Manokin, which differ in chloride uptake in response to salt stress and in combination with Soybean mosaic virus (SMV) and its aphid vector, Aphis glycines . The interaction …

Characterization Of A Novel Fungal-Specific Gene, Fug1, In Fusarium Verticillioides, John Byron Ridenour

Graduate Theses and Dissertations

Filamentous fungi are responsible for numerous plant and animal diseases. The filamentous ascomycete Fusarium verticillioides is a globally important pathogen of maize, capable of causing severe yield reductions and economic losses. Also of substantial concern is the contamination of infected kernels with fumonisins, toxic secondary metabolites linked to toxicoses in humans and livestock. The number of sequenced fungal genomes is rapidly increasing. However, functional characterization of fungal genes has not progressed at a comparable rate. In pathogenic fungi, uncharacterized genes represent a source for novel virulence factors or anti-fungal targets. Therefore, to fully understand the genetic mechanisms underlying fungal pathogenesis, …

Reniform Nematode (Rotylenchulus Reniformis) Manipulation Of Host Root Gene Expression During Syncytium Formation In Upland Cotton (Gossypium Hirsutum), Wei Li

All Theses

Background: The semi-endoparasitic reniform nematode (Rotylenchulus reniformis) is a major yield-limiting pest of multiple crops in the tropics and sub-tropics, including upland cotton (Gossypium hirsutum). Reniform-resistant cotton varieties are urgently needed, but genes that confer resistance to reniform nematode have not been identified in any species. Parasitism by reniform nematode involves significant developmental changes in plant roots, leading to the formation of multicellular feeding structures called syncytia. Here, we present de novo transcriptomes assembled from syncytial and non-syncytial cotton roots on three sampling dates across a 12-day time course. Results: Total mRNA samples extracted from reniform-infected …

Dissection Of Gray Leaf Spot Of Maize Through Functional Genomics, Robert Louis Hirsch

Graduate Theses and Dissertations

Gray leaf spot, caused by Cercospora zeae-maydis, is a devastating disease of maize that reduces yields and increases management costs. C. zeae-maydis penetrates maize leaves through stomata, but the biological and molecular bases of this process are poorly understood. The goal of this research was to elucidate the biological parameters of stomatal infection in C. zeae-maydis, and to identify and characterize novel genetic pathways involved in stomatal sensing and pathogenesis. Histopathological observations of a GFP-expressing strain of C. zeae-maydis during infection of maize indicated that the fungus responded to host-derived stomatal cues during the infection process. C. zeae-maydis was observed …

Spatial Distribution And Genetic Variability Of Reniform And Lance Nematodes In Cotton Agroecosystems, Claudia Holguin

All Dissertations

Rotylenchulus reniformis (reniform nematode) and Hoplolaimus columbus (Columbia lance nematode) are two of the main plant-pathogenic nematode species affecting cotton production in the United States. For the selection and implementation of effective management practices it is important to understand distribution patterns and population genetic structure of these two nematodes in cotton agroecosystems. In a three-year field study, the spatial distribution of reniform nematode was characterized in two commercial fields in South Carolina to determine the effects of relations with soil texture and crop rotation on reniform nematode distribution (Chapter 1). Results of this project suggest that population densities of reniform …

Effect Of Post-Anthesis Fungicide Applications To Manage Fusarium Head Blight In Winter Wheat, Anna Noversoke

Open Access Theses

Fusarium head blight (FHB) of wheat, caused by the fungus Fusarium graminearum, is currently considered one of the most economically important diseases on wheat in the North Central United States. The fungus causes light-weight "tombstone" grains to form and produces the mycotoxin deoxynivalenol (DON), reducing the yield and quality of the grain. Currently, farmers rely heavily on the sterol demethylase Inhibitor (DMI) triazole fungicide Prosaro (Bayer CropScience) to protect their crop from this disease. The optimal fungicide application timing is traditionally believed to be early anthesis - Feekes Growth Stage (FGS) 10.5.1. However, environmental conditions and uneven flowering across a …

Evaluating Green Stink Bug Damage And Insect Abundance In Edamame, Benjamin Carroll Thrash

Graduate Theses and Dissertations

Edamame are an emerging crop in Arkansas, with 2013 planting estimates at 680 hectares. Although edamame are the same species as conventional soybeans grown in Arkansas, differences in use, maturity, and harvest may require creation and implementation of insect pest management approaches that differ from those used in conventional soybean production systems in order for a quality crop to be produced. Studies were conducted to determine a green stink bug damage-density relationship for edamame. Cages were used to confine green stink bugs on field-planted edamame at densities of 0, 2, 6, or 12 green stink bugs per cage (0, 0.55, …

Management Of Root Knot Nematode (Meloidogyne Incognita ) In Indiana Soybeans, David Edgardo Perla Martinez

Open Access Theses

The aim of this project was to evaluate different strategies for management of Root Knot Nematode (RKN) on soybean and tomato in Indiana. Seed treatments were evaluated under field and greenhouse conditions, but no effect on RKN populations was observed. Soybean lines evaluated for resistance to RKN under greenhouse conditions showed that six lines may be resistant to RKN. Four different commercial mustard cover crops were evaluated for their bio-fumigant impact on RKN populations in the production of tomato. Euruca sativa, Cv. Nemat was a poor host of RKN. A positive impact on the vigor of the tomato plants followed …

Potential Susceptibility Of Canna Flaccida And Two Canna Hybrids To Five Species Of Phytophthora, Kristin Van Kampen

All Theses

The costs and need for clean water are increasing for greenhouse, nursery, and agricultural businesses. Runoff from irrigated agriculture and specialty crops also can take a toll on the surrounding environment, because irrigation runoff water can contain high amounts of nutrients, contaminants, and plant pathogens. To assuage the pollution contributed to runoff water and reduce the overall volume of water used, nurseries are starting to reuse irrigation runoff water. For this to be possible, the water first should be treated before reuse. Constructed wetlands are a biological treatment option that employs vegetation to collect, filter, and store runoff water. Some …

Relationship Between 1,3-Dichloropropene And Nitrogen Fertility In Cotton In The Presence Of Root-Knot And Reniform Nematodes, Amanda Michelle Greer

Graduate Theses and Dissertations

The use of soil fumigation for nematode management in cotton (Gossypium hirsutum) has become increasingly popular in recent years in the absence of effective resistant cultivars. While soil fumigation is relatively expensive, lint yields have consistently been improved to make this practice profitable in fields with severe nematode pressure. Growers in southern Arkansas have observed changes in cotton growth patterns when severely infested fields are fumigated. The most noticeable change has been excessive (rank) growth resulting in an increased need for growth regulators, especially where the nitrogen fertilization exceeds standard recommendations. Field studies were conducted between 2007 and 2010 to …

Biology And Control Of Rice False Smut Caused By Ustilaginoidea Virens (Teleomorph Villosiclava Virens), Andrew Clayton Jecmen

Graduate Theses and Dissertations

Rice false smut (FS), a disease caused by Ustilaginoidea virens (Cke.) Takahashi (1896), was first reported in northeastern Arkansas counties in 1997. The first objective of this research was to establish a collection of U. virens isolates from geographically diverse regions of Arkansas. Three U. virens isolates and chlamydospores from `Templeton' and `Clearfield-151' rice cultivars were used to determine the effects of temperature and pH on mycelial growth and germination. A nested-PCR protocol and histological methods were used to determine if U. virens infects and colonizes rice seedlings and spikelets on panicles. The sensitivity of three U. virens isolates was …

Efficacy Of Rice Insecticide Seed Treatments At Selected Nitrogen Rates For Control Of The Rice Water Weevil, Lissorhoptrus Oryzophilus Kuschel, Mallory Elise Everett

Graduate Theses and Dissertations

Seed-applied insecticides are the standard control method used to prevent rice water weevil (Lissorhoptrus oryzophilus Kuschel) injury to rice (Oryza sativa L.) roots, and often results in greater yields than rice that receives no seed-applied insecticide. Yield increases from seed-applied insecticides often occur even when insect pressure is low and should not cause yield loss. The research objective was to evaluate the effect of urea-nitrogen rate and seed-applied insecticide on number of rice water weevil larvae, nitrogen uptake and rice grain yield. Six trials were conducted at the Pine Tree Research Station (PTRS) and the Rice Research Extension Center (RREC) …

Impact Of Early Infestation Of Two-Spotted Spider Mites (Tetranychus Urticae) On Cotton Growth And Yield, Luis Orellana Jimenez

Graduate Theses and Dissertations

Two-spotted spider mites (Tetranychus urticae Koch, 1836) are pests of vegetables, ornamentals, and row crops around the world. Two-spotted spider mites have become an important long-season pests of cotton, causing injury to cotton from an early vegetative stage. In the past eight years, Arkansas cotton acreage treated for spider mites has more than doubled and most of the increase has been attributed to early season infestations. Yield losses of up to 30% have been observed in other studies where spider mite infestation started at third true leaf. Because of the apparent change in this pest's population dynamics, particularly at …

Fungicide Resistance In Botrytis Cinerea From Strawberry - Molecular Mechanisms And Management, Anja Grabke

All Theses

The United States is the largest producer of strawberries worldwide, generating approximately $2.4 billion worth of fruit each year. Strawberry production, however, is often threatened by pathogens. One of the most destructive fungal pathogens is Botrytis cinerea, the causal agent of gray mold disease. The control of gray mold in commercial fields is largely dependent on the application of fungicides, including the dicarboximide iprodione and the hydroxyanilide fenhexamid. Because both fungicides are prone to resistance development, a survey was conducted to determine the occurrence and prevalence of fungicide resistance. Single-spore isolates were collected from strawberry fields in Florida (for …

Identification And Epidemiological Features Of Important Fungal Species Causing Sooty Blotch On Apples In The Northeastern United States, Angela Marie Madeiras

Doctoral Dissertations

The sooty blotch and flyspeck (SBFS) complex causes blemishes on apples in humid, temperate growing regions worldwide. In contrast to flyspeck etiology, the many species of fungi causing sooty blotch (SB) have not been well studied. The first set of objectives in this study was to use PCR to identify SB species isolated from apples and selected reservoir hosts in the northeastern United States, and to identify patterns of species distribution on hosts and among sites. Results indicated that Geastrumia polystigmatis was the predominant species on apples, whereas Peltaster species were more common on reservoir hosts. Species distribution varied among …

Quality Changes In Hermetically Stored Corn Caused By Fungi And Sitophilus Zeamais, Nda-Agyima Addae-Mensah K

Open Access Theses

Hermetic storage has been shown to be effective in controlling insect pests and maintaining grain quality of dry grains at 13% moisture and below. However, the feasibility and use of hermetic storage for grains at intermediate mid-moisture levels under the influence of the sub-Saharan African weather conditions is relatively unknown. Hermetic storage experiments were conducted on grade 1 "6297 and 6333 VT RIB" hybrid corn under controlled temperature conditions at 10 degrees centigrade and 25 degrees centigrade at target approximate moisture content levels of 11, 15, 18 and 21% wet basis for a total storage period of 6 months. Corn …

Investigation Of Macrophomina Phaseolina On Soybeans From A Regional Perspective, Zachary Forbes Sexton

Open Access Theses

The fungal pathogen, Macrophomina phaseolina, causes the disease charcoal rot (CR), which greatly impacts soybean production. Host resistance to CR is the primary means of managing this disease, yet resistance in commercial soybean cultivars in Maturity Groups (MG) I-III is currently unknown. Thirty (30) and sixty-seven (67) entries to the 2012 Wisconsin (MG I-II) and Indiana (MG II-III) Soybean Variety Trials, respectively, were evaluated for resistance to CR using a cut-stem assay. Disease was characterized as an area under the disease progress curve (AUDPC) based on lesion development and resistance assessed in relation to the resistant check (DT97-4290). In each …

Application And Timing Effects Of Qoi And Dmi Fungicides And A Foliar Fertilizer On Overall Plant Health And Grain Yield In Corn, Jason Phillip Geis

Open Access Theses

The use of fungicides on corn has recently increased as a result of higher grain market prices, changes in cropping practices, higher disease incidence and severity, and the availability and marketing claims of new fungicides. Some of the marketed potential "plant health(TM)" benefits include improved tolerance to drought and heat, improved N utilization, and increased stalk strength. Previous studies have displayed delayed canopy senescence, changes in water use efficiency, and reduced ozone damage in controlled environments. Foliar fertilization has also increased in popularity in recent years due to an increase in grain prices, manufacturer claims, and product availability.

Large-scale field …

Effects Of Wheat Grain Moisture: Quality, Germination, And Relationship To Accumulated Growing Degree Days, Kirsten Thomas

Open Access Theses

Bread wheat (Triticum aestivum L.) is a cereal crop of global importance. As global demand increases, it is essential to increase the quality and efficiency of crop production. Harvesting wheat early provides an opportunity for increased grain quality, and it may also allow the grower to double-crop soybean ( Glycine max L.) after wheat more effectively. Our objectives were to determine if harvesting grain early, at high moisture would, 1) increase milling and baking quality and 2) improve germination potential. As a result of these objectives, we will develop a model to predict dry-down of wheat. Five soft red …

The Pythium Suppressive Ability Of Glomus Intraradices In Cherry Tomato Propagation, Stanley Graham

Biological Sciences

No abstract provided.

Characterization Of Putative Defense Genes In Nonvascular Plants, Blaine Harlan

Undergraduate Honors Thesis Collection

Vascular plants have many known defenses against herbivory and pathogen infection. One inducible defense system that has been extensively studied in vascular plants is systemic acquired resistance (SAR), which is a plant-wide response that results in resistance to a wide range of pathogens Many genes that play a role in SAR have been characterized. Although several studies of plant-pathogen interactions in non-vascular plants have occurred, it was not until recently that the existence of SAR was shown in these plants. The goal of the present study was to confirm the presence of homologous defense genes in moss, and to study …

Characterization Of The Role Of Salicylic Acid In Plant-Pathogen Interactions In Moss, Erica Grabinski

Undergraduate Honors Thesis Collection

The central objective of this project is to explore defense systems that are induced in two moss species, Amblystegium serpens and Physcomitrella patens, upon inoculation with the fungus, Pythium irregulare. In vascular plants, systemic defense is associated with the plant hormone salicylic acid (SA). I hypothesize that when the moss are treated exogenously with SA, the organisms will undergo a systemic defense response, which will involve the induction of defense-related genes and increased resistance to future P. irregulare infection, that is directly correlated with the amount of hormone applied. If the role of SA in plant defense in A. serpens …

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 …

Soil Microbial Community Distributions And Disease Suppressiveness In The Coastal Plain Of Georgia, Michael J. Sabula

Electronic Theses and Dissertations

This study compared the soil microbial communities of three vegetation types in the coastal plain of Georgia: 1. crop land actively in use for agricultural production, 2. transitional grassland in early stages of secondary succession, and 3. pristine unmanaged forest land. Microbial species diversity and quantities of microbial DNA were determined from each of these vegetation types at three separate locations near Statesboro, Georgia. Length heterogeneity PCR(LH-PCR) methods and subsequent analysis of fungal, bacterial, and metazoan communities by analysis of similarity (ANOSIM) revealed high within-group similarity by vegetation type, indicating land management intensity and vegetation cover is a strong determining …