Life Sciences Commons^™

Molecular Identification Of Oomycete Species Associated With Woody Plants In Louisiana And Survey Of Oomycete Species Associated With Live Oak Trees Planted On The Louisiana State University Campus, Hamilton Crockett

LSU Master's Theses

Three Oomycetes genera, Phytophthora, Phytopythium and Pythium, contain many important plant pathogens. Historically, Phytophthora infestans, responsible for the great Irish potato famine, and Phytophthora ramorum, causal agent of sudden oak death disease, are the two better-known high impact pathogens. The LSU AgCenter Plant Diagnostic Center (PDC) has been isolating putative Phytophthora and related species from combined root and soil samples collected from various woody ornamentals and trees for over a decade. In August of 2016, Louisiana received torrential rains, which resulted in historic flooding in several southern parishes. During subsequent years, the PDC staff isolated a …

Population Genomic Characterization Of Cercospora Janseana On Rice In The Southern United States, Jacob Searight

LSU Master's Theses

Cercospora janseana is the causative agent of narrow brown leaf spot (NBLS). Effort had been undertaken since the 1940’s to control this disease through resistance breeding in the Southern United States. However, a severe epidemic of NBLS in 2006 inspired renewed focus on managing this disease. One tool for managing this disease has been identified among resistant cultivars, the CRSP-2.1 resistance locus to NBLS. One thing limiting the investment and deployment of CRSP-2.1, and other unknown resistance genes, is the historical observation that resistance to NBLS rapidly breaks-down in the field. Together, the rapid breakdown of resistance to NBLS …

Identification Of Quantitative Trait Loci (Qtls) For Resistance To Bacterial Leaf Streak: Xanthomonas Translucens Using Qtl And Association Mapping In Three Populations Of Soft Red Winter Wheat, Benjamin Tyler Meritt

LSU Doctoral Dissertations

Bacterial leaf streak (BLS) and black chaff, caused by Xanthomonas translucens pv. undulosa (Xtu), can be a very destructive disease of wheat, especially in the warmer, wetter areas of the Southeastern U.S. Yield losses of up to 40 percent have been recorded in some cases in southern wheat growing regions. With no effective agronomic or chemical method of disease control, identification of genetic resistance is seen as a promising solution. Three soft red winter wheat populations (GAWN, ARK-SNP, and AGS 2060- AGS 2035 DH) representative of soft red winter wheat germplasm in the southeastern U.S. developed by …

Comparative Genomics And Virulence Studies Of Streptomyces Soil Rot And Scab Pathogen Species, Natasha Soares

LSU Doctoral Dissertations

Comparative genomic analyses were performed to gain insights into the organization and content of the genome of Streptomyces ipomoeae, the soil rot pathogen that infects sweetpotatoes. Unlike Streptomyces scab pathogens, the thaxtomin phytotoxin gene cluster (txt) in S. ipomoeae does not appear to reside within a genomic island and has diverged from its scab pathogen counterparts. Increased usage of the rare TTA codon, particularly for the txt cluster, suggests greater translational control by the bldA tRNA in S. ipomoeae. Orthologous gene searches and secondary metabolite profiling yielded ortholog groups and metabolite gene clusters that were exclusive …

Effects Of Pesticides On Red Rot Of Sugarcane, Kezia Cristina Da Silva Reis

LSU Master's Theses

Red rot disease of sugarcane, caused by Colletotrichum falcatum, can be an important constraint to crop production. In Louisiana, red rot primarily affects seed-cane and is more severe when billets (stalk sections) are planted rather than whole-stalks. At planting application of seed-treatment chemicals, particularly a combination of fungicide and thiamethoxam insecticide, has improved stand establishment and increased yields in billet plantings in Louisiana. However, information has been lacking on the effect of the treatments on disease development. Greenhouse experiments were conducted in 2020 and 2021 to evaluate stalk rot symptom severity and initial plant growth for billets dip-treated with …

Screening Soybean Cultivars For Resistance To Aerial Blight Caused By Rhizoctonia Solani Ag1-Ia, Kensy D. Rodriguez-Herrera

LSU Master's Theses

Aerial blight, caused by the fungus Rhizoctonia solani AG1-IA, is an economically important soybean disease in the mid-South. The same pathogen also infects other crops commonly rotated with soybeans like rice, corn, and grain sorghum. Rhizoctonia solani AG1-IA is difficult to manage because of its soilborne nature and the production of long-term survival structures, sclerotia. Management has relied on fungicide applications during the season. Still, there is an increasing prevalence of resistance to commonly used strobilurin fungicides and an urgent need to identify soybean cultivars resistant to aerial blight. Since the patchy distribution of the pathogen complicates field cultivar screening, …

Marker-Trait Association Mapping Of Sorghum Mosaic Virus Resistance In Sugarcane, Chenie Zamora

LSU Master's Theses

Mosaic is a potentially devastating disease of sugarcane that had severe economic impact on Louisiana’s sugarcane industry in the 1920’s and has caused periodic problems ever since. The disease is vectored by migrating aphids that transmit Sugarcane mosaic virus (SCMV) and Sorghum mosaic virus (SrMV) in a non-persistent manner. Mosaic in Louisiana is currently caused by strains of SrMV. Mosaic has been controlled primarily by developing resistant cultivars. Recently, mosaic was detected in some near-commercial clones in the cultivar selection program. This prompted extensive screening of breeding program parent populations that detected infiltration of susceptibility and revealed the need for …

Development Of Alternative Materials And Strategies For Enhancing Rice Health, Jobelle S. Bruno

LSU Master's Theses

Bacterial panicle blight (BPB) and sheath blight (ShB) are economically important diseases of rice (Oryza sativa) in Louisiana and other rice-growing regions around the world. However, there are challenges in the current disease management practices for these diseases. Thus, the main goal of this study is to identify new materials and their application methods that effectively suppress BPB and ShB. To achieve this goal, we evaluated the effect of various materials and application methods against the rice diseases. In 2020 and 2021, various materials, such as ascorbic acid (AA), N-acetylcysteine, chitosan, the avirulent strain of Burkholderia glumae 257sh-1 …

Genetic Characterization Of Resistance To Bacterial Panicle Blight And Sheath Blight In Rice Using Qtl Linkage Analysis And Qtl-Seq, John Christian E. Ontoy

LSU Master's Theses

Bacterial panicle blight (BPB) and sheath blight (SB) are major diseases of rice causing significant yield reduction in conducive conditions. Few cultivars have shown reliable resistance to these diseases. In this study, a recombinant inbred line (RIL) population derived from the U.S. cultivars Jupiter (moderately resistant) and Trenasse (susceptible) was investigated to identify genomic regions associated with BPB and SB resistance. Phenotypes in BPB and SB, as well as days to heading (DH), of the RIL population were evaluated in the field. DH was found to be correlated to BPB and SB diseases. BPB was also positively correlated to SB. …

A Rapid Species-Specific Diagnostic Assay For Xylaria Necrophora, The Pathogen Behind Taproot Decline Of Soybean In The Southern United States, Sophie Baron Sheffield

Honors Theses

No abstract provided.

Response Of Roseau Cane (Phragmites Australis) To Two Biotic Stresses: Hyalopterus Pruni And Bipolaris Yamadae, Heather E. Cizek

LSU Master's Theses

Roseau cane (Phragmites australis) is considered an invasive plant because of its ability to replace native plant species. However, in Louisiana it plays an important role protecting coastal infrastructure and being part of the marsh ecosystem in the lower Mississippi River Delta. In recent years, Roseau cane has been affected by a die-off, a problem that has also been reported in some European countries. Possible biotic and abiotic factors that have been associated with the die-off include scale insects, climate change, pollution, salinity levels, and pathogens.

In this research, the individual and combined effect of a foliar disease …

Using Uav Technology Paired With Multispectral Cameras To Assess Crown Rust Epidemics In Oats, Turner A. Graham

LSU Master's Theses

Crown rust, caused by Puccinia cornonata f. sp. avenae, is a common disease of oats (Avena sativa) found virtually everywhere oats are cultivated. This disease has caused yield losses of 10 to 40% worldwide. Early detection is important for effective management. A more recently utilized technology in agriculture is unmanned aerial vehicles (UAVs). UAVs, or drones, equipped with cameras are now being used as a resource to take images of fields to identify pests and other issues that may be occurring. Normalized differentiated vegetative index (NDVI) is a numerical indicator used to determine the vegetative health of …

Influence Of Planting Date, Maturity Group, Harvest Aids And Fungicide Application On Soybean (Glycine Max (L.) Seed Quality, Ana Priscila Campos

LSU Master's Theses

Field studies evaluated the influence of planting date, maturity group, and harvest timing on soybean yield and seed quality at the LSU AgCenter Northeast (NERS), Macon Ridge, and Dean Lee Research Stations in 2018-2020. In addition, the influence of harvest aid and fungicide application on seed quality impact from delayed harvest and environment was investigated at NERS in 2019 and 2020 in both field and environmentally controlled growth chambers. Soybean yield was maximized when maturity group IV and V soybean varieties were planted between Mid-April and Mid-May. Earlier and later planting dates did not result in maximized yield. Planting date …

Understanding The Etiology Of Taproot Decline Of Soybean Caused By Xylaria Necrophora, José E. Ortiz Solórzano

LSU Master's Theses

Taproot decline (TRD) of soybean is caused by Xylaria necrophora. However, the mechanisms by which it infects soybean and produces symptoms are unknown. Symptoms of TRD include foliar interveinal chlorosis and necrosis and root necrosis, yet X. necrophora appears to be restricted to the roots. While Xylaria species are predominantly wood decomposers, a few are pathogens. More importantly, they produce secondary metabolites (SMs) with multiple bioactivities, including phytotoxicity and antimicrobial activity. Preliminary experiments suggested that X. necrophora was producing SMs responsible for TRD symptoms. We evaluated cell-free culture filtrates (CFs) for phytotoxicity on soybeans, testing for changes in chlorophyll …

Isolation Of Foliar Fungi From Roseau Cane (Phragmites Australis) In Coastal Louisiana, David M. Galo Espinal

LSU Master's Theses

Roseau cane (Phragmites australis) is a wild plant with an extensive root system that is useful in areas vulnerable to soil erosion. In Louisiana, this plant plays an important role protecting the coastal infrastructure of the lower Mississippi River delta (MRD). Currently, P. australis growing in the MRD is being affected by a die-off, which has been associated with several biotic and abiotic factors.

Plant pathogenic fungi is a biotic factor that negatively affect plant growth. Therefore, foliar fungi were isolated from plants growing in one die-off affected area (MRD) and two non-affected areas (Pecan Island and Manchac) …

Resistance To Aflatoxin Accumulation In Maize Mediated By Host-Induced Gene Silencing Of Aspergillus Flavus Alkaline Protease And O-Methyltransferase-A Genes, Olanike Omotola Omolehin

LSU Doctoral Dissertations

Aspergillus flavus is a soil-borne fungal pathogen that infects maize and produces aflatoxins. In the current study, portions of the alkaline protease (alk) and the O-methyl transferase (omtA) genes, which are key in A. flavus virulence and aflatoxin biosynthesis, respectively, were targeted for suppression through an RNAi (RNA interference) approach known as Host-Induced Gene Silencing (HIGS). Separate RNAi vectors were designed to carry regions of the alk and omtA gene fragments (Alk-RNAi and OmtA-RNAi) and introduced into B104 maize zygotic embryos. Eight and six transformation events were positive for the alk and omtA transgene, respectively. …

Boxwood Dieback: Molecular Detection, In-Vitro Fungicide Efficacy, And Host Susceptibility For Managing A New Emerging Disease Caused By Colletotrichum Theobromicola, Harleen Kaur

LSU Master's Theses

Boxwood (Buxus spp. L) is one of the most common and widely planted perennial ornamentals in both home gardens and commercial landscapes. Grown for its evergreen, dark green foliage, boxwood cultivation dates back to 4000 BC in Egypt. Although considered hardy, boxwood is susceptible to several plant pathogens. Recently reported boxwood dieback, a fungal disease caused by Colletotrichum theobromicola, has been spreading at an alarming rate within the United States. Boxwood dieback consists of symptoms that resemble to those caused by Phytophthora root rot, Volutella blight, and some abiotic disorders and can be easily misdiagnosed in nurseries and …

Dsrna As A Potential Tool For Cercospora Leaf Blight Management And Elucidation Of A Factors That Contribute To Late Disease Onset In The Reproductive Growth Stage Of Soybean, Marija Zivanovic

LSU Doctoral Dissertations

Cercospora leaf blight (CLB) of soybean (Glycine max L. Merr.), an important disease in Louisiana, is primarily caused by Cercospora cf. flagellaris. The pathogen produces cercosporin, a toxin necessary for fungal virulence. So far, there are few commercial cultivars of soybean with CLB resistance and few effective fungicides to manage this disease. Consequently, alternative management approaches are needed. With that in mind, the first objective was to develop a screening method to compare the effectiveness of bacterially-expressed double stranded (ds) RNAs corresponding to genes associated with cercosporin accumulation (Avr4, CTB1, CTB8, AY-1 and HN-2 …

Phenotypic And Genotypic Characterization Of Aroma And Cercospora Janseana Resistance In U.S. Rice, Christopher Keith Addison

LSU Doctoral Dissertations

Rice is a staple food for over one-third of the world’s population. With the increasing population, plant breeders must continue to breed for improved varieties. The utilization of markers to applied breeding program can increase the efficiency of selection for key traits. The targeted traits for this research include grain aroma and resistance to the fungal disease narrow brown leaf spot (Cercospora janseana). Our objective was to characterize SNP diversity across the BADH2 gene in publicly available sequence data of a collection of 2,932 rice varieties was characterized to determine the number of gene haplotypes in O. sativa. …

Transgenic Control Of Aflatoxin Contamination In Maize Through Host-Induced Gene Silencing Targeting Aspergillus Flavus Genes Encoding Polygalacturonase (P2c) And Versicolorin Dehydrogenase (Aflm), Yenjit Raruang

LSU Doctoral Dissertations

Maize (Zea mays L.) is susceptible to Aspergillus flavus infection and subsequent contamination with aflatoxins, the most potent naturally produced carcinogenic secondary metabolites. Here, the A. flavus gene aflM encoding the versicolorin dehydrogenase in aflatoxin biosynthesis and the p2c gene encoding the polygalacturonase that is involved in infection were selected as targets for suppression through host induced gene silencing (HIGS). A HIGS vector targeting these genes was constructed and introduced into immature B104 maize embryos. Thirteen out of fifteen p2c transformation events and six out of seven aflM events were confirmed positive by PCR. Kernels containing the p2c gene …

Developing Management Strategies For Taproot Decline, Xylaria Sp., In Soybean, Myra Purvis

LSU Master's Theses

Soybean (Glycine max) is one of the most important oilseed crops in the world. Taproot decline is a recently discovered disease caused by Xylaria sp., a novel species located within the Xylaria arbuscula aggregate. Foliar symptoms include interveinal chlorosis and necrosis, and upon further investigation, there are often dead plants adjacent within the row. Many other soybean diseases have similar foliar symptoms; therefore, more examination is usually required for proper identification. Soybean debris from previous years is suspected to be the primary source of inoculum. Plants may be infected at any point during the growing season, often …

Development Of Biological Tools To Promote Rice Health And Growth, Ateet Maharjan

LSU Master's Theses

Sheath blight (ShB - caused by Rhizoctonia solani) and bacterial panicle blight (BPB - caused by Burkholderia glumae) are economically important rice diseases in Louisiana and other rice-growing regions. Fungicides and oxolinic acid are used to manage ShB and BPB, respectively, but these chemical methods are not sustainable economically and ecologically. Besides diseases, plant utilizable nitrogen (N) in the soil is inadequate for optimum crop yield, leading to the use of inorganic fertilizers and making agriculture less sustainable. To develop alternative biological control methods for protecting rice plants from diseases, rice-associated bacteria were screened based on their antagonistic …

Effects Of Silicon And Beneficial Bacteria On Sheath Blight Of Rice And The Microbial Community Of Rice Rhizosphere, Jhonson Leonard

LSU Master's Theses

Sheath blight (ShB), caused by Rhizoctonia solani Kühn, is an economically important soil-borne disease of rice (Oryza sativa) that can cause up to 50 % yield losses. Application of fungicides is the most effective and commonly used method for managing sheath blight. However, the pathogen can develop new resistant strains upon continuous exposure to a fungicide. Moreover, the use of inorganic fungicides is not eco-friendly. The utilization biological control agents (BCAs) can be a more sustainable and safe means of managing ShB. To develop alternate strategies for ShB management, I am exploring the effect of the silicon (Si) …

Characterization Of The Integrated Signaling Network Of Burkholderia Glumae For The Regulation Of Virulence-Related Function In The Bacterial Pathogenesis Of Rice Plants, Tiago De Paula Lelis

LSU Doctoral Dissertations

Bacterial panicle blight of rice (BPB) caused by Burkholderia glumaeis a major bacterial disease of rice in many rice-producing areas worldwide. Managing the disease is still very difficult due to the lack of effective methods. B. glumaestrains show phenotypic and genomic variations; however, little variation was detected in the known virulence-related genes. In the present study, the complete genome of B. glumae257sh-1, a natural avirulent strain, was sequenced and analyzed. Several spontaneous mutations in the regulatory genes of these avirulent strains were identified. Presumably, the accumulation of these mutations can have a negative effect on the normal …

The Tripartite Interaction Between Arbuscular Mycorrhizal Fungi, Rice, And Insects, Lina Bernaola Alvarado

LSU Doctoral Dissertations

Losses caused by pests remain an important limitation to achieving high rice yields in the United States. Arbuscular mycorrhizal fungi (AM fungi) are able to modify plant physiology by increasing plant growth or inducing defense responses against insect herbivores. However, studies of the role of AM fungi in agroecological factors, including natural occurrence, plant resistance, soil dependency, and plant tolerance, with specific regards to pests that feed on rice plants have not been conducted before. A three-year study revealed natural occurring colonization by AM fungi on rice roots sampled in four rice-producing areas in the southern United States. Overall, rice-AM …

Development Of Sheath Blight-Resistant Breeding Lines For Southern U.S. Environments And Morphological And Genetic Survey Of Giant Salvinia Populations In Louisiana And Texas, Dominique Clark Galam

LSU Doctoral Dissertations

The southern US environment is a very conducive environment for agriculture and fisheries. Rice farming, shrimping and water related activities help drive the local economy. However, there are several factors that impede the success of these activities. Sheath blight (SB) disease caused by Rhizoctonia solani is one of the major biotic constraints to high grain yield and quality for most commercial U.S. rice varieties. Although different breeding lines with high levels of "partial resistance" have been developed none has been used directly as a commercial variety. The first research objective of this research was to identify and develop advanced breeding …

Investigations Into Aspergillus Flavus Infection Of Corn And Regulation Of Aflatoxin Production By Volatiles And Biocontrol Strains, Rebecca R. Sweany

LSU Doctoral Dissertations

Aspergillus flavus is an ascomycete fungus impacting agriculture, public and environmental health due to production of acutely-toxic, carcinogenic aflatoxins in oil seed crops, especially corn in Louisiana, and lung infections of immunocompromised patients resulting in a leading cause of AIDS patients’ deaths globally. The most effective aflatoxin mitigation strategy, biocontrol by atoxigenic A. flavus presents several concerns including: dissemination of a human pathogen, possible sexual reproduction and reliance on precise environmental conditions. Several aspects of A. flavus biology were investigated to potentially improve treatments. Studies investigated how genotypically diverse members within the A. flavus population interact with other population members …

Distribution And Incidence Of Mosaic And Evaluation Of Susceptibility In Louisiana's Current Sugarcane Germplasm, Jancee Rice

LSU Master's Theses

Mosaic is a viral disease of sugarcane caused primarily by Sorghum mosaic virus (SrMV) in Louisiana. Low mosaic incidence has resulted from successful breeding for resistance. However, mosaic was detected in breeding program experimental clones and a new cultivar, HoCP 09-804.Therefore, multiple research approaches were undertaken to assess the current status of mosaic in Louisiana sugarcane and prevent it from re-emerging as an important problem. Field surveys conducted during 2016-2018 of breeding program yield trials and experimental clone seed-cane increases determined disease incidence and distribution. Mosaic was detected in three of five sugarcane production areas and incidence ranged from 0 …

Occurrence Of Putative Endornaviruses In Non-Cultivated Plant Species And Characterization Of A Novel Endornavirus In Geranium Carolinianum, Rachel Herschlag

LSU Master's Theses

Endornaviruses are RNA viruses, which can infect plants yet cause no apparent symptoms. To date, most descriptions of endornaviruses infecting plants have been in cultivated species. A survey for endornaviruses in non-cultivated plants was initiated in 2015 and continued through 2017 in Baton Rouge, Louisiana. Two hundred and seven plant species were tested for distinctive dsRNA profiles by selective extraction and gel electrophoresis, of which seven contained endornavirus-like dsRNA. RT-PCR amplification of an endornavirus-specific sequence supported the endornavirus nature of six of the seven samples. Of the six host species, one species, Geranium carolinianum was confirmed as being infected with …

Distinguishing Isolates Of Rotylenchulus Reniformis Endemic In Louisiana On The Basis Of Root-Associated Females And Egg Masses, Benjamin Mcinnes

LSU Master's Theses

The reniform nematode Rotylenchulus reniformis is a major pathogen of soybean and cotton in Louisiana. Previous studies have shown that populations of reniform nematode throughout the southern United States vary in reproduction and pathogenicity. Limited studies have been conducted to evaluate the reproduction and pathogenicity of populations of R. reniformis endemic in Louisiana. Studies with isolates of the nematode from eight cotton-producing parishes focused solely on reproduction of the root-associated infective and swollen female life stages with and without attached egg masses on the cotton genotypes MT2468 Ren3, M713 Ren5, and Stoneville 4946GLB2 and the soybean genotypes PI 548316, PI …