Plant Pathology Commons^™

Understanding Variability In Geographic Isolate Of Rotylenchulus Reniformis Across The Us Cotton Belt, Sagar Gc

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Management of the reniform nematode (Rotylenchulus reniformis Linford and Oliveira) in cotton (Gossypium hirsutum L.) is a challenge since the resistant cultivars lack uniformity in nematode suppression when tested across multiple geographical regions. The central hypothesis of this study was that regional variability in performance of resistant cotton cultivars is associated with unique reproduction biology (reproduction and virulence) of R. reniformis from distinct geographic origins. Greenhouse studies were conducted to assess differential reproduction biology among nine geographic population of R. reniformis originated from South Carolina (SC), Alabama (AL), Florida (FL), Arkansas (AR), Georgia (GA), Louisiana (LA), Texas (TX), …

Breeding For Disease Resistance In Melon And Watermelon, Venkata Rao Ganaparthi

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Watermelon and cantaloupe are two widely consumed cucurbits, but their acreage in the United States reduced by nearly 50% in last two decades. Fusarium wilt caused by a soil borne pathogen Fusarium oxysporum f. sp. niveum(Fon) race 2 is a major limiting factor in watermelon production as it reduces yields by 80%. Grafting watermelon plants onto the root stock of wild, disease-resistant varieties like ‘Carolina Strongback’ is the best strategy to manage Fon race 2. Though effective, this approach increases production costs.

Part of this dissertation focused on finding more sustainable, cost-effective solutions to control Fusarium wilt …

Interactions Of Biorational And Synthetic Dmi Fungicides For Control Of Fruit Diseases, Johanna Wesche

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Biological fungicides are increasingly investigated as sustainable alternatives to synthetic fungicides in fruit crop protection. This dissertation examines the interactions between two commercial biological fungicides, Bacillus subtilis AFS032321 (Theia) and metabolites of Pseudomonas chlororaphis AFS009 (Howler EVO); and demethylation inhibitor (DMI) fungicides, with a focus on compatibility, synergistic potential, and resistance implications. In vitro assays revealed that commonly used DMI fungicides difenoconazole, metconazole, tebuconazole, and propiconazole inhibited vegetative growth of B. subtilis at concentrations above 50 µg/ml, whereas mefentrifluconazole promoted colony expansion. Under controlled conditions, lesion development on detached fruit was inhibited synergistically when Theia was combined with the growth-promoting …

Maximizing Crop Production And Profitability Through Double Cropping Corn And Soybean Systems In South Carolina, Bennett Harrelson

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Profitability is critical for farm sustainability, efficiency, and longevity. Over the last decade, corn and soybean commodity prices have fluctuated considerably, and more recently, extreme increases in input prices have narrowed profit margins. Non-traditional cropping systems that can boost profit are becoming of interest to farmers in South Carolina, specifically double cropping soybean behind corn. In this scenario, corn is harvested at high moisture contents and followed by ultra-late planted soybean. However, prior research related to the agronomic production practices of double cropping corn and soybean is minimal. To develop best management practices for growers interested in double cropping corn …

Investigate The Use Of Nucleic Acids As Pesticides To Manage Major Pests And Pathogens Of Crops In South Carolina, Prasanna Valavanur Shekar

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The sugarcane aphid (SCA, Melanaphis sorghi), first discovered on grain sorghum in late 2013, has gradually become a major insect pest of sorghum. It inflicts significant damage to the crop year after year, causing millions of dollars in losses throughout the sorghum-producing regions of the United States. Similarly, Armillaria root rot—also referred to as oak root rot—is a major cause of decline in peach (Prunus persica) production in the southeastern United States. This disease is caused by Armillaria mellea and Armillaria tabescens. Current management practices for controlling M. sorghi include the use of synthetic pesticides, resistant varieties, and regular scouting. …

Investigate The Possibility Of Producing Healthier, Safer Peanuts Through Molecular Breeding And Novel Fungal Pathogen Management Strategies, Tariq Alam

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Peanut allergy, a critical health concern with high morbidity and mortality rates, is a leading cause of fatal anaphylactic reactions in the United States. Managing peanut allergy is challenging due to the prevalence of peanuts in processed foods and the risk of contamination. This dissertation evaluates the U.S. peanut mini-core collection for four major immunogenic proteins, Ara h1, Ara h2, Ara h3, and Ara h6, using gel electrophoresis, enzyme-linked immunosorbent assay, liquid chromatography, and mass spectrometry. The study identified 26 genotypes with reduced concentrations of allergenic proteins. Genome-wide association studies (GWAS) of protein traits revealed 10 significant SNPs and identified …

Exploring Mechanisms Of Chemical Resistance In Xanthomonas Arboricola Pv. Pruni And Strategies To Mitigate Resistance And Improve Disease Control, Milan Panth

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Xanthomonas arboricola pv. pruni (XAP) is a phytopathogenic bacterium that causes bacterial spot of peach. It causes spotted lesions on leaves and fruit, leading to early defoliation and unmarketable fruit, respectively. The pathogen can overwinter in twig cankers, which serve as the primary initial inoculum source for the next season’s leaf and fruitlet infection. The current disease management practice mainly relies on routine application of chemical bactericides containing copper or oxytetracycline (OTC) in the growing season. However, disease incidence can still be high despite chemical control measures in warm, rainy seasons.

Frequent applications of copper and OTC in United …

Investigating The Etiology, Epidemiology, And Ecology Of Blackberry Yellow Vein Disease In South Carolina, Wanita Dantes

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Blackberry production is growing in popularity in the southeastern U.S. However, blackberry growers in this region report major problems with productivity and longevity due to viruses. First, the state of knowledge on blackberry yellow vein disease (BVYD) complex, associated with mixed infections of a diverse group of viruses, is discussed. Specific viruses associated with symptom types are unknown. Therefore, the etiology of BYVD is not fully understood, which makes BYVD diagnosis challenging. My research focused on improving BYVD diagnosis, etiology, and epidemiology. Second, I developed a farm-level diagnostic protocol to improve virus disease surveillance. High throughput sequencing detected 17 known …

Epidemiological Approaches For Practical Solutions To Pertinent Peanut Problems, Hope Becton

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Peanut is an important food crop grown in the southeastern region of the United States. Diseases are the most yield-limiting component in peanut production with one of the most important being late leaf spot (LLS), caused by Nothopassalora personata (Np). The disease initially appears in the lower canopy as dark brown to black lesions and conidiophores bearing conidia are produced on the abaxial side of the lesion. Np is passively dispersed primarily by wind and rain events. Spore traps were used to detect and quantify conidia captured up to 70 m from an inoculum source and to further assess …

Unveiling The Potential Of Calcium And Natamycin For Botrytis Blight Management On Cut Roses, Melissa Munoz

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Botrytis blight caused by the fungus Botritys cinerea is the most devastating disease of cut roses. The extensive use of fungicides used for Botrytis blight management during cut rose production and postharvest represents a severe threat in terms of fungicide resistance development as has been previously reported. Additionally, health concerns for growers and the environment are growing in recent years making consumers more aware of the fungicides in the products that they consume including ornamentals. This scenario highlights the importance of searching for alternative products to synthetic fungicides. During this research, the use of calcium as an alternative management strategy …

Etiology And Epidemiology Of Mini-Ring In Ultradwarf Bermudagrass Putting Greens, Lukas Dant

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Mini-ring is a disease in ultradwarf bermudagrass (UDBG) [Cynodon dactylon (L.) Pers. × C. transvaalensis (Burtt-Davy)] putting greens caused by Waitea zeae (Voorhees) J.A. Crouch & Cubeta, (formerly Rhizoctonia zeae). Symptoms typically resemble frog-eye patches that are 10 to 40 cm in diameter with a bronze to orange outer ring and green center. In the southeastern United States, mini-ring symptoms appear in late-summer and generally persist until UDBG dormancy in late-fall. Mini-ring is often problematic in UDBG when nitrogen (N) fertility is reduced to manage organic matter production and improve putting green performance and perceived green speed. While …

Distribution And Management Of Phytophthora Species On Lavender In The United States, Daniel Dlugos

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Phytophthora root and crown rot (PRCR) is currently the most important disease on lavender (Lavandula spp.) in the United States. The disease was first described on English lavender (L. angustifolia) in a Maryland nursery in 1991, with Phytophthora nicotianae as the causal agent. Since that time, the disease has been reported on multiple continents and as caused by several species of Phytophthora. This study examined the distribution and pathogenicity of Phytophthora species on lavender in the United States, requested lavender grower feedback regarding their production and concerns, and examined efficacy of selected management options. Lavender …

Nematicidal Activity Of Extracts From Phytolacca Americana On Five Plant-Pathogenic Nematode Species Of Economic Importance, Saleh Ahmed

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Plant-parasitic nematodes cause significant losses to plant agriculture annually. The limited availability and high cost of synthetic nematicides, along with the environmental risks associated with their use, have created a renewed interest in the search for alternative management tactics. One such alternative tactic is the use of plant extracts. The focus of this research is the evaluation of the nematicidal activity of water extracts from Pokeweed (Phytolacca americana). In vitro and greenhouse tests were performed to evaluate the effects of the extracts on five species of plant-pathogenic nematodes of economic importance: Aphelenchoides fragariae, Ditylenchus dispsaci, Meloidogyne incognita, Pratylenchus penetrans, and …

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

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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 …

The Foliar Nematode Aphelenchoides Fragariae: Studies On Facultative Feeding And Desiccation Tolerance, Zhen Fu

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The foliar nematode Aphelenchoides fragariae is an economically important and frequent pest of ornamental crops. In nurseries and landscapes in the United States, foliar nematodes can be a serious problem affecting hostas (Hosta spp.), a common perennial ornamental plant that thrives in shady environments. Fundamental research on the biology and ecology of this nematode provides the basis for development of sound management strategies. The general objective of this dissertation was to study two behaviors that make foliar nematodes very successful as plant pests: desiccation tolerance and alternative feeding on fungi (or facultative feeding on the plant). To study the molecular …

Biology, Histopathology, And Improvements In Axenic Culture Of Labyrinthula Terrestris, Causal Agent Of Rapid Blight Of Cool-Season Turfgrasses, Kirthi Kiran Yadagiri

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Rapid blight is a disease of cool-season turfgrasses caused by Labyrinthula terrestris. Disease symptoms include water-soaked lesions, yellowing and browning of foliage, and coalescing patches of dead turf. L. terrestris belongs to a group of marine microorganisms in the kingdom Chromista (also known as Stramenopila). Morphological characteristics of Labyrinthula spp. include spindle-shaped vegetative cells that move in an ectoplasmic network. The biology and pathology of L. terrestris is not clearly understood; therefore, the ultrastructure, life cycle, and histopathology of L. terrestris were investigated. In addition, improvements in axenic culture and long-term storage methods were made to better culture L. terrestris. …

Population Variability Of Rotylenchulus Reniformis In Cotton Agroecosystems, Megan Leach

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Rotylenchulus reniformis, reniform nematode, is a highly variable species and an economically important pest in many cotton fields across the southeast. Rotation to resistant or poor host crops is a prescribed method for management of reniform nematode. An increase in the incidence and prevalence of the nematode in the United States has been reported over the last two decades. However it is not clear whether the observed increase is related to the emergence of novel populations that are more aggressive or have a higher fitness or shifts in host availability or susceptibility. The objectives of this research were to determine …