Plant Sciences Commons^™

Dissecting Salt Tolerance In Soybean By Profiling Differential Physiological Responses Under Salt Stress, Jade Amber Newsome

Graduate Theses and Dissertations

Saline soils are common worldwide and limit the yield potential of many crops. Plants respond in a variety of ways to the stress imposed by saline soils. Plants under salt stress must first sense their surroundings and transmit a signal alerting the rest of the plant to the saline conditions. Salt tolerance in soybeans is typically defined by exclusion of chloride ions from foliar tissues. Though differences in ion uptake among soybean genotypes is well documented, the key mechanisms employed by tolerant cultivars to cope with salt stress on the whole-plant level are still largely unknown. Objectives of the current …

Genetic Basis Of Biosynthesis And Cytotoxic Activity Of Medicago Truncatula Triterpene Saponins, Brynn Kathleen Lawrence

Graduate Theses and Dissertations

Saponins are a large family of specialized metabolites produced in many plants. They can have negative effects on a number of plant pests and are thought to play a role in plant defense. With current and possible future uses in industry and agriculture, saponins have also been shown to be hypocholesterolemic, hypoglycemic, immunostimulatory, antioxidative, anti-inflammatory, and cytotoxic. In spite of their usefulness, our understanding of the genetic basis for saponin biosynthesis is still incomplete. We generated recombinant populations with parents from genetically distinct accessions of Medicago truncatula, with either high or low accumulation and varying profiles of saponins. Primers for …

Genetic Analysis Of Soybean Mosaic Virus (Smv) Resistance Genes In Soybean [Glycine Max (L.) Merr.], Mariola Klepadlo

Graduate Theses and Dissertations

Soybean mosaic virus (SMV) causes the most serious viral disease in soybean worldwide. Seven SMV strains, G1 - G7, and three independent multi-allelic loci for SMV resistance, Rsv1, Rsv3, and Rsv4, have been identified. In the initial study, 299 soybean germplasm lines were genotyped for Rsv4 region, inoculated with SMV-G1 and G7 strains, and classified into several resistance groups. The Glyma.02g121400 locus was sequenced from ten soybean accessions, and alignment of the sequences revealed three SNPs displaying 100% polymorphic consistency when a soybean genotype carrying the Rsv4 gene was present. A cross between V94-5152 × Lee 68 was made to …

A Comparative Study Of Medicago Truncatula Transcriptomes As They Relate To Saponin Defenses Against Insect Pests, Audra Mae Rogers

Graduate Theses and Dissertations

Triterpene saponins are a class of defensive plant-derived compounds, which have a

variety of functions including antimicrobial, insecticidal, and nematicidal activities. This

research assessed the performance of the beet armyworm, Spodoptera exigua, following ad

libero feeding on Medicago truncatula accessions differing in specialized metabolite and

saponin profiles. Insect performance did not directly relate to the foliar saponin levels in the

accessions, which was measured using HPLC mass spectrometry. Accession ESP105 had the lowest foliar saponins overall, yet had similar levels of soyasaponins compared to the other accessions. Conversely, accessions A17, PRT178, and GRC43 had high foliar saponins with particularly high …

The Effects Of Meloidogyne Incognita And Heterodera Glycines On The Yield And Quality Of Edamame In Arkansas, Juliet Fultz

Graduate Theses and Dissertations

Edamame (Glycine max), also known as vegetable soybean, was introduced to the United States from Japan in 1890 and has been growing in popularity as a nutrient-rich, low-sugar snack in recent years. In 2012, the American Vegetable Soybean and Edamame, Inc. established the first domestic commercial processing plant in Mulberry, Arkansas and contracted local growers for production. Since the crop is harvested when seed are immature, management practices are different from those for traditional soybean. Plant-parasitic nematodes, particularly Meloidogyne incognita (southern root-knot) and Heterodera glycines (soybean cyst), are common in Arkansas and are pests of concern for edamame growers. Edamame …

Rice Blast Disease In The U.S. And Africa: Determination Of Pathogen Diversity And The Identification Of Resistance Genes For Disease Management, Felix Rotich

Graduate Theses and Dissertations

Rice blast caused by Magnaporthe oryzae (= Pyricularia oryzae) B. Couch, is a leading disease of rice. Magnaporthe oryzae exhibits a high degree of diversity. The diversity of isolates of M. oryzae from Africa and the U.S. were examined using vegetative compatibility and virulence phenotyping as well as determination of variation in the avirulence gene AVRPiz-t in isolates from Africa. Also, evaluation of blast resistance genes in the interspecific rice germplasm “New Rice for Africa” NERICA was done using F2 progeny of the cross of U.S. susceptible cultivar M204 and NERICA 12. The U.S. isolates were in three vegetative compatibility …

The Role Of G-Protein Signaling In Pathogenesis In Cercospora Zeae-Maydis, Brant Smith

Graduate Theses and Dissertations

Gray leaf spot, caused by Cercospora zeae-maydis, is one of the most destructive foliar diseases of maize worldwide. C. zeae-maydis orients hyphal growth towards stomata (stomatal tropism) and forms infectious structures (appressoria) that are necessary for successful infection. Although some genes involved in pathogenesis in C. zeae-maydis have been identified, the molecular mechanisms are not well understood. In fungi, heterotrimeric G-proteins consist of three subunits (α, β, and γ) and mediate responses to environmental stimuli. They regulate diverse functions, including nutrient detection, virulence, fungal development, conidiation, secondary metabolism, and pathogenesis in many plant pathogenic fungi. This research explored the role …

Understanding The Causal Agent Of Rose Rosette Disease, Patrick Louis Di Bello

Graduate Theses and Dissertations

A number viruses are known to infect roses, ranging from those in the genera Nepovirus, and Ilarvirus, which have been reported since the inception of rose virology, to recently discovered viruses in the genera Carmovirus, Closterovirus, Emaravirus, Luteovirus, Rosadnavirus, and Potyvirus. Of the viral diseases in rose, arguably the most damaging is Rose rosette (RRD), which is associated with the Emaravirus, Rose rosette virus (RRV). The objective of this thesis is to fill in the gaps in knowledge on the epidemiological aspects of RRD and RRV. There has been significant progress in the epidemiology of the RRD agent prior to …

Blackberry Virosome: A Micro And Macro Approach, Archana Khadgi

Graduate Theses and Dissertations

Viruses pose a major concern for blackberry production around the world with more than 40 species known to infect the crop. Virus complexes have been identified recently as the major cause of plant decline with blackberry yellow vein disease (BYVD) being the most important disease of the crop in the Southern United States. The objective of this research was to study the blackberry virosome in both the macro and micro scale. The large scale approach involves identification of the major viruses known to be associated with BYVD in the Southern United States as well as the identification of other viruses …

Soybean Seed Quality And Vigor: Influencing Factors, Measurement, And Pathogen Characterization, Kimberly Ann Cochran

Graduate Theses and Dissertations

High seed vigor (SV), or the ability of seed to germinate and grow in a stressful environment is important, as many field emergence conditions are stressful for germination. Soybean SV can be affected by cultivar, seed storage environment conditions, the growing environment during seed development, crop management practices such as foliar fungicide applications, pathogens, and other factors. To assess the effects of some of these factors on soybean, the objectives of this work were to determine 1. the effect of cultivar and foliar azoxystrobin application on soybean yield, germination, vigor, microflora, and their relationships under harvest delay conditions; 2. if …

Pythium: Characterization Of Resistance In Soybean And Population Diversity, Keiddy Esperanza Urrea Romero

Graduate Theses and Dissertations

Pythium spp. are an important group of pathogens causing stand losses in Arkansas soybean production. New inoculation methods and advances in molecular techniques allow a better understanding of cultivar resistance and responses of Pythium communities to cultural practices. The objectives of this research were to i) characterize the resistance of soybean to P. aphanidermatum with two phenotyping assays that evaluated the seed rot phase of the disease; and ii) understand the effect of long term crop rotation on species diversity and iii) to determine the effect of location, temperature and continuous soybean and soybean-rice rotation on Pythium spp. diversity in …

Effect Of Nitrogen Fertilizer Rates And Two-Spotted Spider Mite Incidence On 'Strawberry Festival' Strawberry Cultivar Performance, Megan E. Mcgovern

Graduate Theses and Dissertations

The decline in strawberry (Fragaria x ananassa Duch.) production in Arkansas over the last 50 years has sparked an interest in the use of season extension techniques to improve yield and fruit quality. High tunnel strawberry production has the potential to become a profitable and sustainable production system; however, information on nutrient and pest management is limited.

The overall objective of this study was to determine the response of ‘St. Festival’ strawberry cultivar to different nitrogen fertilizer rates in order to develop a fertilization program for strawberries grown under high tunnel production systems. Experiments were conducted at the University of …

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 …

The Effects Of Salinity On Pythium Disease Of Rice And Soybean, Terea Jeanette Stetina

Graduate Theses and Dissertations

Increasing salinity is an important factor limiting agricultural productivity worldwide. In addition to direct effects on growth and yield, diseases also may be affected. This study characterized the effects of soil salinity on seedling disease of soybean and rice caused by Pythium spp. Controlled environment experiments on soybean used two cultivars which differed in chloride tolerance and soil treated with a CaCl₂ solution to create a range of electrical conductivity (EC) levels. For soybean, soil was either not infested or infested with Pythium sylvaticum or P. aphanidermatum (pathogenic to soybean), or P. oligandrum (not pathogenic to soybean). Twenty-one days …

Effects Of Rain And Simulated Rain On Deoxynivalenol Levels In Grain And Chaff Of Winter Wheat With Fusarium Head Blight, Manoj Kumar Pun

Graduate Theses and Dissertations

Wheat grain affected by Fusarium head blight (FHB) contains the mycotoxin deoxynivalenol (DON) that is harmful to humans and animals. Reducing the amount of DON in grain is the goal of management practices for FHB so it is important to understand the factors affecting DON in grain. Some studies on the effects of late-season moisture found increases in DON while others found decreases due to leaching. The objectives of this study were to determine effects of late-season rain and misting on DON concentration in wheat spike tissues and to quantify the amount of DON leached from spikes. Field experiments were …

Molecular And Biochemical Mechanisms Of Pathogenesis In The Maize Foliar Pathogen Cercospora Zeae-Maydis, Winfred-Peck Dorleku

Graduate Theses and Dissertations

GLS is a serious foliar disease of maize, a major staple crop grown commercially in the USA for both human and animal feed production, and increasingly, for ethanol production. The disease is caused by two Cercospora species, C. zeae-maydis and C. zeina, both of which infect maize in the USA and in other parts of the world, with yield losses potentially greater than 50%, depending on local conditions. In culture, C. zeae-maydis produces a phytotoxic, host non-specific perylenequinone, cercosporin, and abscisic acid (ABA), for which there is no known pathological or physiological function in the fungus. Experimental evidence indicates …

Spatial Distributions Of Rhizoctonia Species In Soybean Fields Undergoing Annual Rotations With Rice, Terry Neil Spurlock

Graduate Theses and Dissertations

Aerial blight is caused by Rhizoctonia solani AG1-IA. This pathogen also causes sheath blight of rice. In Arkansas, many soybean and rice fields undergo an annual rotation of these two crops which facilitates a continuous source of inoculum from one year to the next. Aerial blight is a two stage disease in that R. solani AG1-IA colonizes the plant during the early vegetative growth stages and then aerial blight develops after the soybean canopy closes in the later reproductive stages of development. As a result of the upper portion of the canopy often being asymptomatic, significant yield loss can occur …

Soybean (Glycine Max) Response To Imazosulfuron Drift And Carryover From Rice (Oryza Sativa), Sandeep Singh Rana

Graduate Theses and Dissertations

In the Midsouth, soybean is often grown in close proximity to rice or in rotation with rice. Herbicides used in rice can injure soybean via drift or carryover. Consequently, field trials were conducted to determine the response of soybean (cv. AG 4703) to imazosulfuron drift and carryover (at Fayetteville, Marianna, Keiser and Pine Tree, AR) from rice. To assess the potential for carryover, soybean was planted into rice fields treated the previous year with imazosulfuron (rotation study). To evaluate in-season sensitivity of soybean to imazosulfuron (tolerance study) relative to halosulfuron, a common sulfonylurea herbicide applied to rice, both imazosulfuron and …

Abiotic And Biotic Factors Affecting The Japanese Beetle In Arkansas, Bryan Mathew Petty

Graduate Theses and Dissertations

Japanese beetles are a relatively new pest to Arkansas. During my Ph.D. research I investigated the pathogens and environmental factors influencing Japanese beetle populations in the state. The prevalence of various pathogens and parasitoids attacking Popillia japonica were recorded annually from wild populations. Of specific interest was the microsporidian pathogen Ovavesicula popilliae, which I introduced as a biological control agent in the state. Details of the relationship between this pathogen and the Japanese beetle were investigated, including dose response, host range, and spore production. Additionally, annual abundance of the beetle in the region was recorded and tracked over the course …

Distribution And Control Of Glyphosate-Resistant Johnsongrass (Sorghum Halepense) In Arkansas Soybean, Dennis Brent Johnson

Graduate Theses and Dissertations

Johnsongrass, once the most persistent and troublesome grass weed of row crops throughout the southern U.S., has previously been confirmed resistant to the acetolactate synthase (ALS) and acetyl-coenzyme A carboxylase-inhibiting herbicides in the Midsouth and has recently evolved resistance to glyphosate in Arkansas. The goal of this research was to establish the geographical distribution of herbicide-resistant johnsongrass in Arkansas and to develop herbicide programs for controlling glyphosate-resistant johnsongrass in Arkansas soybean. Johnsongrass accessions were collected from 14 counties in the Mississippi River Delta region of Arkansas and screened for resistance to four of the most commonly used postemergence herbicides for …

Morphological And Molecular Taxonomic Identification And Phylogenetics Of Criconematoidea, Marco Cordero

Graduate Theses and Dissertations

The superfamily Criconematoidea has been studied since 1886. It is composed of two families: Criconematidae (subfam. Criconematinae, Hemicycliophorinae) and Tylenchulidae (subfam. Tylenchulinae, Paratylenchinae and Tylenchocriconematinae). Multiple species in genera have been identified and differences and similarities have been found. Species belonging to genera Mesocriconema and Criconemoides show very few differences making their identification difficult. Seventy two populations were studied. They were collected in Arkansas and/or received from the following states: California, Florida, Kansas, Missouri, North Carolina and Tennessee. Populations of the following species were identified: Mesocriconema curvatum, M. kirjanovae, M. onoense, M. ornatum, M. sphaerocephala, M. surinamense, M. vadense, M. …

Initial Fine Mapping Of The Spinach Downy Mildew Resistance Locus Rpf1, Wei Yang

Graduate Theses and Dissertations

Spinach is an important vegetable crop grown in many parts of the world (Correll et al. 2011). It has become increasingly popular due to its nutritional value as it is very high in antioxidants (Prior, 2003). Spinach production, however, is affected by many biotic stresses. Downy mildew, caused by Peronospora farinosa f. sp. spinaciae (Pfs) , is perhaps the most important biotic constraint for spinach production worldwide (Correll et al, 1994). As of 2012, 14 races of Pfs have been reported (Correll et al., 2011). The rapid increase of new races is likely a direct result of substantial changes in …

Genetic Diversity Of Seed Dormancy And Molecular Evolution Of Weedy Red Rice, Te Ming Tseng

Graduate Theses and Dissertations

Rice is the grain with the third-highest global production. In the US, Arkansas is the largest rice producing state; however, an estimated 62% of the rice fields in the state are infested with red rice, and can cause up to 80% yield reduction in rice. Among its weedy traits, seed dormancy plays an important role in its persistence, and helps red rice escape weed management techniques thereby increasing the red rice soil seedbank. Red rice also has the potential to hybridize among themselves and with cultivated rice, thus resulting in diverse phenotypes and genotypes. In this study we measured variation …

Characterization And Epidemiology Of Soybean Vein Necrosis Associated Virus, Jing Zhou

Graduate Theses and Dissertations

Soybean vein necrosis disease (SVND) is widespread in major soybean-producing areas in the U.S. The typical disease symptoms exhibit as vein clearing along the main vein, which turn into chlorosis or necrosis as season progresses. Double-stranded RNA isolation and shot gun cloning of symptomatic tissues revealed the presence of a new tospovirus, provisionally named as Soybean vein necrosis associated virus (SVNaV). The presence of the virus has been confirmed in 12 states: Arkansas, Illinois, Missouri, Kansas, Tennessee, Kentucky, Mississippi, Maryland, Delaware, Virginia and New York. Symptomatic samples collected from eight states (AR, IL, MO, MS, KS, TN, MD and DE), …

Effects Of Associated Subcortical Beetles On Oviposition Behavior And Early-Stage Survival Of Sirex Nigricornis F. (Hymenoptera: Siricidae), Ace J. Lynn-Miller

Graduate Theses and Dissertations

Sirex (Hymenoptera: Siricidae) woodwasps develop within xylem of host conifers. Sirex females drill through the bark, phloem and into xylem tissues where they deposit eggs along with a symbiotic Amylostereum fungus. The presence of Amylostereum is necessary for successful development of Sirex immatures as the larvae are unable to derive adequate nutrition from xylem in the absence of the fungus. The Eurasian woodwasp, Sirex noctilio F., was discovered in northeastern North America in 2004. Sirex noctilio has caused significant economic damage in Pinus radiata D. Don plantations of the southern hemisphere, but is of little economic significance in its native …

False Smut Of Rice: Histological Analysis Of Infection, Liem Thi Thanh Nguyen

Graduate Theses and Dissertations

False smut of rice, caused by Ustilaginoidea virens (Cooke) Takahashi (Teleomorph: Villosiclava virens), has become a common disease in most major rice growing regions throughout the world. Considerable confusion exists regarding the infection process and the disease cycle. Therefore, a clearer understanding of pathogenesis caused by Ustilaginoidea virens is critical for future efforts to develop genetic and chemical tools to manage false smut in Arkansas and other regions of the world. The overall goal of this research was to clarify the infection process underlying false smut, with emphasis on comparing and contrasting the histological basis of root and foliar infections. …

Effects Of Felled Shortleaf Pine (Pinus Echinata Mill.) Moisture Loss On Oviposition Preferences And Survival Of Sirex Nigricornis F. (Hymenoptera: Siricidae), Jessica Hartshorn

Graduate Theses and Dissertations

The European woodwasp, Sirex noctilio F. (Hymenoptera: Siricidae) utilizes pine as its host during larval development. Females drill through pine bark to deposit eggs, a symbiotic fungus, Amylostereum, and phytotoxic mucus into the tree. In their native range, these insects are not viewed as primary pests because they attack dead or dying trees. Over the last century, this woodwasp has been accidentally introduced into several countries in the southern hemisphere. Some regions have incurred millions of dollars in damage to large plantations of the widely planted pine species, radiata pine (Pinus radiata D. Don). Sirex noctilio was discovered …

Effects Of Meloidogyne Incognita, Soil Physical Parameters, And Thielaviopsis Basicola On Cotton Root Architecture And Plant Growth, Jianbing Ma

Graduate Theses and Dissertations

The root-knot nematode, Meloidogyne incognita, and the seedling pathogen, Thielaviopsis basicola, commonly co-exist in Arkansas cotton fields and may interact resulting in increased losses. The primary objective of this research was to evaluate the effects of soil physical parameters on these soilborne pathogens and cotton growth in controlled environmental, field, and microplot studies. Controlled environmental experiments used two soil bulk densities and four pathogen treatments: non-infested soil, soil infested with M. incognita or T. basicola and soil infested with both pathogens. The results indicated bulk density generally did not affect seedling growth or disease since soils had low penetration resistance …

Effects Of Environment And Genotype On Charcoal Rot Development On Soybeans, Micah Diane Doubledee

Graduate Theses and Dissertations

Charcoal rot of soybean, caused by the soilborne fungus Macrophomina phaseolina (Tassi) Goid, is a disease associated with high soil temperature and low soil moisture. Above-ground symptoms, which can be difficult to distinguish from drought symptoms, include low vigor, dead leaves that remain attached to the plant, early senescence and yield loss. Irrigation limits damage, but does not prevent colonization of the tissue by the pathogen. No soybean line is immune to M. phaseolina, but a few lines may have moderate resistance. The objectives of this research were to 1) determine the effects of genotype and drought on the development …

Flight Period And Species Composition Of Sirex (Hymenoptera: Siricidae) And Associated Deladenus (Nematoda: Neotylenchidae) Within Arkansas Pine Forests, Danielle Keeler

Graduate Theses and Dissertations

The European woodwasp, Sirex noctilio F. (Hymenoptera: Siricidae), which is a known destructive pest of pine in the southern hemisphere was recently discovered in the eastern United States. Before we can understand how S. noctilio may affect pine forests throughout the United States, we need a better understanding of native Sirex and the role they play in the ecosystem. The objectives of this research were to 1) determine species composition and flight period for native Sirex; 2) confirm presence of parasitic nematodes, Deladenus (Nematoda: Neotylenchidae), within adult Sirex; 3) investigate Deladenus parasitism rates; 4) verify the number of Deladenus species …