Plant Pathology Commons^™

Watermelon Fungicide Guide, Anthony Keinath, Anna Sara Hill

Horticulture

The foliar diseases gummy stem blight, powdery mildew, anthracnose, and downy mildew can reduce watermelon yields in South Carolina. Specific fungicides are needed to manage each disease. This spray guide will assist growers, Extension agents, and crop consultants recommend the appropriate fungicides based on disease symptoms and signs.

Identification, Pathogenicity, And Fungicide Sensitivity Of Itersonilia Perplexans Associated With Petal Spot Of Gerbera Cut Flowers In Colombia, Matheus Beger

All Theses

Petal diseases significantly affect gerbera cut flower production, as minor visual damage renders flowers unmarketable. Among those pathogens causing petal spots, Itersonilia perplexans affects some Asteraceae plants. However, this pathogen's impact on Colombian gerbera remains poorly studied. This study was designed to fill four gaps: molecular identification of Colombian isolates, confirmation of pathogenicity, standardized culture media, and fungicide sensitivity data. Four objectives were pursued: (i) isolate and identify the causal agent through sequencing the Internal Transcribed Spacer, Small Subunit and Large Subunit from the rDNA; (ii) evaluate pathogenicity on detached gerbera petals; (iii) identify optimal culture media for I. perplexans …

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

All Dissertations

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), …

The Development Of Tools For The Production Of Fusarium Oxysporum Race 4 Resistant Cotton Varieties, Thomas Rylands

All Theses

Fusarium oxysporum race 4 (FOV4) is a fungal pathogen that infects cotton (Gossypium spp.) plants, resulting in fusarium wilt (FW) disease that causes significant wilting, yield loss, and eventually death. Since cotton is such an important crop globally, with tens of millions of bales of fiber produced and sold worldwide each year, it is critical to develop effective strategies to combat this pathogen. This research aims to achieve that goal through two projects: (i) develop an efficient co-culture system to test fungal treatments in vitro, and (ii) develop a computer vision pipeline to more accurately assess plant resistance …

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

All Dissertations

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

All Dissertations

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

All Dissertations

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 …

Anaerobic Soil Disinfestation As A Non-Chemical Management Option Against Fungi And Heterotrophic Bacteria In Organic Sweetpotato Production, Meredith Tucker

All Theses

North Carolina is the largest producer of sweetpotatoes in the United States, with South Carolina increasing farming acreage to 2,501 in 2022 compared to 1,300 in 2017. Growers producing conventional and organic sweetpotatoes are equally challenged with managing fungal pathogens due to fungicide resistance or fungicides being unavailable due to environmental regulations, leading many to shift to growing organic crops. Anaerobic soil disinfestation (ASD) is a non-chemical pre-plant management option that uses a carbon amendment, irrigation, and plasticulture to establish an anaerobic environment in soils, killing soil microbes. A greenhouse study was conducted to assess ASD on fungal pathogens and …

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

All Dissertations

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. …

Evaluation Of Pierce’S Disease-Resistant Grapevine Cultivars In Upstate South Carolina, Annie Bruno

All Theses

Interest in wine grape production is increasing in South Carolina, but Pierce’s Disease (PD) caused by the xylem-limited bacteria Xylella fastidiosa (Xf) is a major limiting factor. Xf is spread by sap-sucking insect vectors in the Cicadellidae family such as sharpshooters. In the United States, Xf has become endemic to the southeast as global temperatures rise, causing winter temperatures to increase, which allows the bacteria to survive year-round. However, PD-resistant grapevine hybrid cultivars have become available through breeding V. vinifera genes with native American Vitis species that are resistant to Xf. In this study, the PD-resistant grapevine …

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

All Dissertations

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 …

Field Prevalence Of Ring Nematodes In South Carolina And Its Potential To Predispose Peanut Pods To Aflatoxin Contamination, Sarala Giri

All Theses

Peanut ring nematode, Mesocriconema ornatum is a nematode pest of peanut which can cause necrotic lesions on pods, pegs, and roots. It has been reported to facilitate secondary infections in peanut and other crops resulting in more significant losses in yield and quality. Aspergillus flavus is a ubiquitous facultative saprophyte that produces aflatoxin, the most problematic mycotoxin for global health and economy. Experiments were conducted at the Edisto Research and Education Center of Clemson University to examine the relationship of ring nematode populations at pegging and harvest with aflatoxin concentration in peanut kernels due to infection by A. flavus …

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

All Dissertations

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 …

Survey Of Nematodes Associated With Strawberry In South Carolina And Evaluation Of Short-Term Heat Exposure On Nematode Reproduction Biology, Ivan A. Alarcon Mendoza

All Theses

Nematodes are a growing threat to the multi-billion-dollar strawberry industry in the US due to the lack of safe and effective management methods. Limited information on the distribution of nematodes in fumigated plasticulture strawberry fields further complicates their management. Additionally, climatic anomalies like rising soil temperatures and heat waves are occurring more often, and their impact on crop growth and nematode reproduction is not well understood. The current study was conducted with two main objectives: i) understand distribution and population densities of nematodes associated with plasticulture strawberry production in South Carolina, and ii) understand the impact of short-term high heat …

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

All Dissertations

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 …

Transcriptomic Profile Of Armillaria Root Rot Fungi Affecting The U.S. Stone Fruit Industry, Jared Weaver

All Theses

Armillaria Root Rot (ARR) is a significant replant disease threatening the future of the United States stone fruit industry. Economic loss in South Carolina peach orchards is estimated to be $8M annually due to approximately 3-4% of annual tree deaths caused by ARR on replant sites. Management solutions are insufficient and can at best extend the life of the orchards on replant sites. The only solution to solving the ARR problem, apart from abandoning the replant site for peach production, is planting orchards on ARR-resistant rootstock. Significant progress has been made towards providing growers with genetically resistant rootstock, however, for …

Identification And Characterization Of Geotrichum Candidum Isolates From Peach With Reduced Sensitivity To Propiconazole, Sara Price

All Theses

Geotrichum candidum Link (1809) is a yeast-like fungus that causes sour rot of stone fruits, including peach (Prunus persica). The disease caused damage between 2021 and 2023 to the peach crop kept in cold storage at a commercial farm in South Carolina despite preharvest and postharvest applications of fungicides. Isolates from 41 symptomatic fruit, from a South Carolina (SC) commercial packing house, as well as other isolates obtained from South Carolina were identified to be G. candidum based on species-specific PCR amplifications of the β tubulin gene. Commonly used postharvest fungicide fludioxonil had no effect on G. candidum mycelial growth …

Screening For Dmi And Mbc Fungicide Resistance In Monilinia Fructicola And Evaluation Of Biorational Products For Control Of Brown Rot On Peach In The Southeast United States, William Gura

All Theses

Monilinia fructicola (G. Winter) Honey is a fungal pathogen and is the causal agent of blossom blight, twig blight, green fruit rot, preharvest brown rot, and postharvest brown rot of peach (Prunus persica (L.) Batsch). Especially pre-and postharvest brown rot can have devastating economic impacts and negatively effects yield for peach growers throughout the southeastern United States. The most effective method for the control of pre- and postharvest brown rot is the application of synthetic fungicides during preharvest season. However, the consecutive use of fungicides with the same mode of action potentially give rise to resistance. This thesis focuses …

Use Of Biorational Products For Botrytis Management In Floriculture Crops, Josselyn Calidonio

All Theses

Botrytis cinerea is an important pathogen that has a significant economic impact on the floriculture industry from propagation to the postharvest environment. Chemical fungicide applications have been one of the main approaches that growers use for botrytis blight management; however, studies have shown that the indiscriminative use of these chemicals leads to fungicide resistance (Brent and Hollomon, 1998; Fillinger and Elad 2016). This thesis explores the potential use of biorational products for botrytis blight management. Biorationals are defined as compounds that have low or no direct mammalian toxicity and few effects on the environment (Paulitz and Belanger 2001). A review …

Evaluating The Effect Of Biochar Soil Amendments On Belonolaimus Longicaudatus Populations Damaging Bermudagrass In South Carolina, Malone Thomason

All Theses

Belonolaimus longicaudatus Rau, (1958) (sting nematode) is a prevalent plant-parasitic nematode found in association with Cynodon spp. (bermudagrass) in South Carolina (Ye et al., 2012). Due to the persistence of the pest, long-term management strategies are necessary. Applications of biochar and compost amendments have reduced nematodes in various crop systems, but research on turfgrass systems is limited. The objectives of the studies were to determine: (1) The effect of topdressing or soil incorporated biochar amendments on sting nematode populations, and (2) The effect of topdressing or soil incorporated amendments on turf quality. A field study was established to examine topdressings …

Management Of Nematodes Associated With Tobacco And Sweet Potato Using Non-Fumigant Approach, Md Shah Alam

All Theses

Tobacco and sweet potato are attacked by several species of plant-parasitic nematodes leading to substantial yield losses. Because host-plant resistance is lacking in commercial cultivars and other common methods of nematode management either have low efficacy or pose adverse effects to the environment, controlled environment studies were conducted to evaluate the efficacy of non-fumigant chemical and biological nematicides against Meloidogyne enterolobii on tobacco and Rotylenchulus reniformis on sweet potato. Results suggest that fluensulfone was the most effective in suppressing M. enterolobii in tobacco, followed by oxamyl and fluopyram. The biological Burkholderia derived biological nematicide did not suppress the nematode population. …

Laser Inscribed Graphene Aptasensor For Detection Of Apple Stem Pitting Virus, Yifan Tang

All Theses

Apple stem pitting virus (ASPV) is a latent RNA virus that could cause significant loss to apple production; early-stage field diagnosis could reduce the economic loss caused by ASPV infection. Biosensor is a promising user-friendly detection tool that could transduce biological or chemical interactions into electric signals. Among various types of biosensors, aptasensor, which use aptamers as recognition elements show potential as a high throughput, in-field test. The goal of this thesis is to develop an electrochemical aptasensor testing system for ASPV detection. The quality control study of laser inscribed graphene (LIG) based working electrode of the biosensor was conducted …

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

All Dissertations

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 …

In Vitro Rooting Techniques In Prunus Spp. For Propagation And Disease Screening For Armillaria Root Rot (Arr) Resistance, John Lawson

All Theses

Prunus is a genus widely cultivated to produce edible fruit including almond (P. amygdalus), peach (P. persica (L.) Batsch), cherries (P. avium and P. cerasus), among others. The cultivation of Prunus is economically important for several regions of the United States and relies on appropriate cultivars and rootstocks that are adapted to a growing region. Encroaching plant pathogens are forcing breeders to use sexually compatible germplasm from related species for introgression of novel alleles that confer tolerance or resistance. This is especially true in the rootstock breeding where interspecific hybridization is often used …

Addressing Meloidogyne Enterolobii Spread In The Sweetpotato Industry: Development Of A High Throughput Survey Detection Method For Root-Knot Nematodes And Quantification Of M. Enterolobii Damage On Storage Roots In Long-Term Assays, Julianna Culbreath

All Theses

Meloidogyne enterolobii is an aggressive root-knot nematode (RKN) species that has emerged as a significant pathogen of sweetpotato in the Southeastern US. Meloidogyne enterolobii is spread through the movement of infected ‘seed’ sweetpotatoes used for propagation, and the RKN resistance in commercial sweetpotato cultivars has proven ineffective against this nematode. This has prompted regulatory agencies to impose quarantines on regions infected with M. enterolobii. Sweetpotato storage roots can be rendered unmarketable due to M. enterolobii infection, resulting in potential overall yield loss. Visual detection of RKN in sweetpotato can be unreliable, and further distinguishing M. enterolobii from other RKN species …

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

All Dissertations

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 …

Characterization Of Colletotrichum Nymphaeae Isolates From Apple With Reduced Sensitivity To Fluazinam And Tebuconazole, Rulyu Meng

All Theses

Apple bitter rot is caused by Colletotrichum nymphaeae and other Colletotrichum species and management relies primarily on synthetic pesticides. Very few fungicides are effective against the disease and resistance has further limited their usefulness. A recent study indicated relatively low EC₅₀ values (the concentration required to inhibit 50% of mycelial growth in vitro) of C. nymphaeae isolates from Brazilian apples to fluazinam and tebuconazole, two fungicides that are not routinely used for bitter rot control. Isolates on opposite sides of the sensitivity range were designated either sensitive (lowest EC₅₀ values) and reduced-sensitive (highest EC₅₀ values). The objective …

Understanding The Influence Of Excessive Fertilization And Water Relations On Peach (Prunus Persica (L.) Batsch) Skin Bronzing, Sydney Lykins

All Theses

This project evaluated possible causes of peach skin bronzing, a brown-blotchy skin discoloration on mid to late-season peaches that causes drastic decreases to grower incomes in the Southeastern U.S. It is known that there is no bacterial, insectile, viral, or fungal cause of bronzing; thus, these studies focused on potential nutrient imbalances within the peach. On the ‘PF23’ variety, factors of irrigation, potassium fertilization, and transpiration-inhibiting sprays were tested to see the various effects on the incidence and severity of bronzing. The hypothesis was that excessive irrigation and excessive soil potassium concentrations would induce a higher incidence and severity of …

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

All Dissertations

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 …

Characterization Of Colletotrichum Nymphaeae Isolates, Causal Pathogen Of Apple Bitter Rot, With Reduced Sensitivity To Fluazinam And Tebuconazole, Rulyu Meng

All Theses

Apple bitter rot is caused by Colletotrichum nymphaeae and other Colletotrichum species and management relies primarily on synthetic pesticides. Very few fungicides are effective against the disease and resistance has further limited their usefulness. A recent study indicated a relatively low range of EC₅₀ values (the concentration required to inhibit 50% of mycelial growth in vitro) of C. nymphaeae isolates from Brazilian apples to fluazinam and tebuconazole, two fungicides that are not routinely used for bitter rot control. Isolates on opposite sides of the range were designated either sensitive (lowest EC₅₀ values) and reduced sensitive (highest EC_{50 …}