Digital Commons Network^™

Ammonium Chemotaxis In Chlamydomonas Reinhardtii, Gabela Nelson

LSU Doctoral Dissertations

Analysis of ammonium chemotaxis in Chlamydomonas reinhardtii is largely hindered, compared to that of phototaxis, despite equal importance on flagellated microalgal physiology. A major contribution of this shortfall is the lack of proper assay method. We developed a simple Petri dish assay method in which light is homogenously exposed while patterns of the cellular migration are tracked with a function of time. Using the method, new findings were revealed. First, this research presented that a strain lacking the eyespot organelle required for light gradient-sensing exhibits similar chemotactic behavior compared to a wild-type strain, suggesting Chlamydomonas sense an ammonium gradient not …

Genetic Dissection Of Alkalinity Tolerance In Rice (Oryza Sativa L.), Lovepreet Singh

LSU Doctoral Dissertations

Alkaline stress is a major threat to rice production globally. The resources for genetic improvement of alkalinity tolerance in rice are limited. We performed genome-wide association study (GWAS) and QTL mapping integrated with whole genome sequencing and expression analysis to identify and confirm QTLs and candidate genes. We developed a near-isogenic line (NIL) population to fine map the two important QTLs. In GWAS experiment, we genotyped and phenotyped a panel of indica and japonica genotypes for alkalinity tolerance and identified genomic regions and candidate genes conferring alkalinity tolerance. Principal component analysis revealed that alkalinity tolerance score, shoot dry weight, and …

The Characterization Of Selected Α- And Β-Carbonic Anhydrases Of Arabidopsis Thaliana, Hiruni Weerasooriya

LSU Doctoral Dissertations

Carbonic anhydrases (CAs) are zinc-metalloenzymes that interconvert two inorganic carbon (Ci) species, CO₂ and HCO₃^-. In Arabidopsis thaliana, there are eight αCA genes, six βCA genes, three γCA genes, and two γCA-like genes. The majority of CA research in plants has focused on finding a link between CA activity and photosynthesis rates. Since the CA genes are expressed in different plant tissues and multiple CA isoforms are distributed among various organelles of the plant cell, I hypothesize that CAs facilitate CO₂ diffusion among cell compartments and maintain Ci pools for carbon-requiring reactions by interconverting …

Evaluating The Pesticide-Induced Outbreak Of Soybean Looper, Chrysodeixis Includens (Walker) (Lepidoptera: Noctuidae), In Louisiana Soybean, Scott Lee

LSU Doctoral Dissertations

Soybean looper, Chrysodeixis includens (Walker), has established itself as the primary lepidopteran defoliator in Midsouth soybean agroecosystems. Pesticide-induced outbreak events associated with this pest have been observed by soybean producers. The insecticides believed to prompt these incidents are routinely used for the control of other co-occuring pests, such as stink bugs. Outbreak conditions present soybean producers with conflicting management decisions for pests. Laboratory, greenhouse, and field experiments were conducted to provide a better understanding of insecticide usage impact on populations of C. includens and the arthropod community. To discern the potential mechanisms behind C. includens outbreak, a baseline for the …

The Effects Of Tillage And Cover Crops On Crop Yield And Soil Properties In Wheat Double-Cropping Systems, Peters E. Egbedi

LSU Doctoral Dissertations

This three-year study was conducted on a commerce silt loam soil at the Northeast Research and Experiment Station near St. Joseph, Louisiana to evaluate the following objectives: 1) evaluate crop yield response to tillage, winter, and summer cover crops in wheat double-cropping systems. 2) evaluate the effects of tillage, winter and summer cover crops on soil properties under different cropping systems. 3) quantify the economic benefits of double-cropping, cover cropping and monoculture systems under conventional and no tillage practices. A winter cover crop (WCC) mix (winter wheat (Triticum aestivum and Austrian winter pea (Pisum sativum) and summer …

Spatiotemporal Transcriptome Diversity And Responses To Salinity Tolerance In The Extremophyte Schrenkiella Parvula, Chathura Wijesinghege

LSU Doctoral Dissertations

Schrenkiella parvula is an extremophyte model related to the most widely studied plant model, Arabidopsis thaliana and Brassica crops in the mustard family (Brassicaceae). It can thrive in highly saline environments where the soil is enriched in Na⁺, K⁺, Li⁺, borates, and chlorides. Understanding how this extremophyte can survive high salinity with genomic adaptations can provide insight into developing stress resilient crops in the future. Gene expression of S. parvula in response to salt has been investigated using shoot and root tissue from mature vegetative-phase plants. However, prior studies have not examined the transcript …

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 …

The Effects Of Drought And Shade On Bottomland Hardwood Regeneration, Charles Joseph Pell

LSU Doctoral Dissertations

Floodplain forests support a high diversity of tree species adapted to regenerate under fluctuating water and light availability. Regeneration regulates species composition, and shade and flood tolerance influence the likelihood of regeneration. Regeneration failure of shade-intolerant and flood-tolerant tree species commonly occurs in southcentral and southeastern floodplain forests of the United States, also known as bottomland hardwoods (BLHs). In many BLHs reduced flooding has resulted in a dryer floodplain. These changes in flooding are linked to recent shifts in species composition. The mechanisms controlling regeneration in BLHs and these composition shifts are poorly understood. In a controlled germination experiment, I …

Integration Of Remote Sensing Approaches For In-Season Nitrogen Management, Murilo De Santana Martins

LSU Doctoral Dissertations

Nitrogen (N) management is being conducted at flat rate in Louisiana due to practicality and convenience, but the price of N fertilizer and high breakeven costs are forcing producers to find ways to reduce costs and optimize N application. In this scenario, precision agriculture technologies, specifically the use of optical sensors on board of unmanned aerial systems (UAS) to variable rate N application on farm is showing a promising approach to save inputs and reduce environmental impacts. However, the general goal of this research was to develop and evaluate in-season N management approaches for N recommendation in corn (Zea …

Genetic Dissection And Qtl Pyramiding To Enhance Salinity Tolerance In Rice (Oryza Sativa L.), Sandeep Chapagain

LSU Doctoral Dissertations

Salinity is emerging as a major threat to rice production worldwide due to climate change and anthropogenic sources. We performed three different population development approaches using exotic salt tolerant donors in US rice backgrounds to identify the salt tolerant QTLs/genes and tolerant breeding lines. First approach involved development of a biparental introgression lines (ILs) population by utilizing a salinity tolerant donor ‘TCCP’ in an elite rice cultivar ‘Cheniere’ background and mapping of QTLs at germination, seedling, and reproductive stages A total of seven QTLs for five germination traits, 16 QTLs for seven seedling stage traits, and 30 QTLs for ten …

The Importance Of Co2 Recapture In The Co2 Concentrating Mechanism Of Chlamydomonas Reinhardtii, Ashwani Rai

LSU Doctoral Dissertations

The aim of this thesis is to investigate the CO₂ concentrating mechanism (CCM) of Chlamydomonas reinhardtii and to develop a quick method for estimating the activity of carbonic anhydrases (CAs). The first project demonstrates that there are two almost identical mitochondrial CAs in C. reinhardtii, CAH4 and CAH5, that help to maintain photosynthesis and minimize the leak of CO₂ generated by respiration and photorespiration. We used an RNAi approach to reduce the expression of CAH4 and CAH5 so that their physiological functions could be studied. RNAi mutants with low expression of CAH4 and CAH5 have impaired rates …

Sodium Mediates Developmentally Plastic Responses In Plants And Herbivores, Luis Santiago-Rosario

LSU Doctoral Dissertations

Sodium plays a crucial role in organismal performance, trophic-level interactions, and eco-evolutionary dynamics. For plants, sodium impacts osmoregulation, growth, and water uptake. For animals, sodium is essential influencing osmoregulatory processes, muscle and neural development, and blood regulation. My dissertation aims to disentangle why sodium mismatch affects resource-consumer interactions and its influence on morphological and behavioral plasticity. First, I identified how sodium impacts plant performance and sodium accumulation strategies. I initially focused my research on understanding how increasing substrate sodium affects plant growth and tissue sodium accumulation strategies in controlled settings using a systematic review approach. I found that saltier plants …

Weed Management With Pro-Herbicides Benzobicylon And Florpyrauxifen-Benzyl In Louisiana Rice Production, William Bradley Greer

LSU Doctoral Dissertations

Field studies were conducted in 2020 and 2021 to evaluate benzobicyclon tolerance to 71 weedy rice accessions collected from Louisiana and southern Arkansas. Benzobicyclon was applied at 373 g ai ha^-1 as a postflood application on 3- to 4-leaf rice. At 28 DAT, less than 15% control was observed on 70% of the accessions and 80% or better control was observed on 3% of accessions. Inconsistent weedy rice control can be attributed to the presence or absence of a functional HIS1 allele. The functional HIS1 allele was present in 96% of accessions when treated with benzobicyclon control was less …

Impact Of New Technologies On Weed Control In Louisiana Rice Production, David C. Walker

LSU Doctoral Dissertations

Field studies were conducted in 2018-2021 at the LSU Agricultural Center’s H.R. Caffey Rice Research Station (RRS) near Crowley, LA, and the Dean Lee Research and Extension Center (DLREC) near Alexandria, LA to evaluate off-target florpyrauxifen movement on soybean. Soybean was treated with florpyrauxifen at the V4-V5 or R1-R2 growth stages. Soybean injury was evaluated at 1, 7, 14, and 28 days after treatment (DAT) and soybean plant height (cm) was recorded at 7, 14, and 28 DAT. At soybean maturity, yield and individual yield components were subjected to regression analysis to describe the relationship between florpyrauxifen rate and soybean …

Multi-Year Data Analysis And Genomic Selection To Improve The Efficiency Of A Rice Breeding Program, Tommaso Cerioli

LSU Doctoral Dissertations

Plant breeding dramatically improved crops performances during human history and will play a pivotal role in shaping the future of agriculture. However, this activity requires large amount of time and resources. The availability of multi-year datasets and abundant DNA information enables new analyses and breeding approaches that can increase the productivity and efficiency of a breeding program. In recent years, the LSU Rice Breeding Program has implemented marker assisted selection (MAS) and genomic selection (GS) to predict performance of rice genotypes before field testing. The goal of this project was to conduct analyses and test molecular approaches to increase the …

Investigation Of Arabidopsis Extremophyte Relatives, Schrenkiella Parvula And Eutrema Salsugineum Reveals Different Roads Leading To Salt Stress Tolerance, Kieu-Nga Thi Tran

LSU Doctoral Dissertations

How plants adapt to salt stress has been a central question in plant biology for decades. Yet we have not been able to fully understand the molecular networks and genetic mechanisms underlying this complex trait. Most of the genetic work on salinity stress has focused on understanding salt stress responses in the leading, yet a salt-sensitive model Arabidopsis thaliana. With the recent availability of genomes for wild-relatives of A. thaliana, we can now investigate how naturally salt adapted plants may have evolved modified or novel molecular networks to adapt to salt stress. Therefore, my research utilizes a comparative …

Insights Into Abscisic Acid And Phosphatidic Acid Signal Transduction Dynamics In Arabidopsis Thaliana, Ruth Wanjiru Ndathe

LSU Doctoral Dissertations

Abscisic acid (ABA) is a plant hormone that triggers a signaling transduction in response to drought, salinity, and cold. The core components in the ABA signaling pathway that lead to downstream ABA responses have been identified.

Phosphatidic acid (PA) is a membrane phospholipid that is involved in the signaling pathway for ABA-induced stomatal closure. We tested whether PA is involved in the signaling pathway for ABA-induced gene expression as well, using model plant Arabidopsis thaliana. We selected the RD29A gene which is a canonical drought gene that is induced by ABA. We found that PA is not involved in …

Investigating Plant Tolerance For The Management Of Insect Pests In Rice, James Michael Villegas

LSU Doctoral Dissertations

The rice water weevil, Lissorhoptrus oryzophilus Kuschel (Coleoptera: Curculionidae), is the most destructive and widespread insect pest of rice (Oryza sativa L., Poaceae) in the USA. This insect poses a global threat to rice production, having invaded rice-producing regions of Asia and Europe. Moreover, lepidopteran stemborers, particularly the invasive Mexican rice borer, Eoreuma loftini (Dyar) (Lepidoptera: Crambidae), are increasingly becoming problematic in Louisiana rice. Although insecticidal seed treatments have been widely used against weevils and stemborers, alternative management strategies are needed. Plants possess defense-related traits that both reduce injury from herbivores (resistance) and the amount of yield loss per …

Integrated Nutrient Management And Cover Cropping Practices In Louisiana Sugarcane Production Systems, Daniel Erneso Forestieri

LSU Doctoral Dissertations

Integrating effective fertilizer management with conservation practices is essential to improve farm income and promote environment friendly sugarcane production systems. A study was conducted in multiple to document the impact of nitrogen (N) source and cover cropping on sugarcane yield and quality components. The treatment consisted of different N sources: urea, knife-in urea ammonium nitrate (UAN) solution, calcium nitrate-CaNO3, ammonium sulfate-NH4SO4, and knife-in UAN. + foliar N, applied at 90 kg ha-1 and control (0 N). The cover crops included: crimson clover (Trifolium incarnatum), hairy vetch (Vicia villosa), and oilseed radish (Raphanus sativus L.) planted at 13, 17, and 1 …

Palynology And Paleoclimatology Of The Chicxulub Impact Crater In The Early Paleogene, Vann Smith

LSU Doctoral Dissertations

At the end of the Cretaceous Period, a large bolide impacted the Earth and formed the Chicxulub impact crater in the Yucatán Peninsula, Mexico. In 2016, International Ocean Discovery Program (IODP) Expedition 364 Site M0077 drilled into the buried peak ring of the crater, recovering a marine Paleocene to early Eocene post-impact section deposited on top of the impact breccia. Palynological analysis of 195 samples from the post-impact section has yielded the first pre-Holocene vegetational record from inside the Chicxulub impact crater and the first palynological record of the recovery of life following the end-Cretaceous mass extinction from inside the …

Understanding Potassium Toxicity Stress Responses Of The Extremophyte Schrenkiella Parvula Using Systems Biology Approaches, Pramod Pantha

LSU Doctoral Dissertations

Schrenkiella parvula is an extremophyte model closely related to Arabidopsis thaliana and Brassica crops. Its natural habitat includes shores of saline lakes in the Irano-Turanian region. It has adapted to grow in soils rich in multiple salts including Na⁺ and K⁺. I have investigated the genetic basis for high K⁺ tolerance in plants using S. parvula as a stress tolerant model compared to the premier plant model, Arabidopsis thaliana which is highly sensitive to salt stresses using physiological, ionomic, transcriptomic, and metabolomic approaches. Under high K⁺ stress, root system architecture changes significantly compared to control …

The Effect Of Fallow Season Cover Crops On Nutrient Cycling And Soil Health In Row Crop Production In The Mid-South, Kritsanee Iamjud

LSU Doctoral Dissertations

The reliance on conventional cropping has profoundly impacted agricultural sustainability and resulted in soil degradation. Winter cover crops can preserve the soil surface, recycle soil nutrients, and improve soil health. Hence, the role of cover crops in Louisiana row-crop production was examined in small-scale plots and large-scale on-farm studies at three sites in Northeast Louisiana from 2017 to 2020. Additionally, mixed cover crops degradation and nutrient release were evaluated at Macon Ridge and Dean Lee sites to determine the optimum time of nutrient availability after cover crop termination. The small-scale results showed that integrating cover crops for corn (Zea …

Silicate-Solubilizing Bacteria In Louisiana Soils: Identification, Profiling, And Functions In Crop Production, Jayvee A. Cruz

LSU Doctoral Dissertations

Studies were conducted to determine the potential of silicate-solubilizing bacteria (SSB) as biostimulant in Louisiana rice (Oryza sativa L.) production systems. Isolation and profiling of SSB in Louisiana soils; evaluation on its effects on the silicon (Si) uptake and productivity of rice using various carriers derived from slag, rice hull, and sugarcane (Officinarum spp.) bagasse; and development of a feasible approach of incorporating SSB to the rice production system were conducted. Results showed that numerous bacteria isolated from Louisiana soils can solubilize silicate and produce multiple plant growth-promoting compounds. These potential SSBs were identified into four genera: Aeromonas, …

Zein And Lignin-Based Nanoparticles As Delivery Systems: Pesticide Release And Nanoparticle Health Impact On Soybean Plants, Fallon Polette Salinas Gonzalez

LSU Doctoral Dissertations

This research examined the effect of biodegradable, polymeric, lignin-based nanoparticles (LNPs, 113.8±3.4, negatively charged) and zein nanoparticles (ZNP, 141.6±3.9, positively charged) on soybean plant health. The LNPs were synthesized from lignin, covalently linked to poly(lactic-co-glycolic) acid by emulsion evaporation. ZNPs were synthesized by nanoprecipitation. Soybeans grown hydroponically were treated with three concentrations (0.02, 0.2, and 2 mg/ml) of NPs at 28 days after germination. The effect of ZNPs and LNPs on plant health was determined through analysis of root and stem length, chlorophyll concentration, dry biomass of roots and stem, as well as carbon, nitrogen, and micronutrient absorption after 1, …

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. …

Identification Of Blda As A Major Regulator Of Virulence In The Sweetpotato Soil Rot Pathogen Streptomyces Ipomoeae And Characterization Of Distinct Clostridium Sweetpotato Soft Rot Isolates, Kuei-Ting Yang

LSU Doctoral Dissertations

Streptomyces ipomoeae is the causative agent of Streptomyces soil rot on sweetpotato, a disease characterized by extensive necrosis of both adventitious and storage roots. While Streptomyces potato scab pathogens produce a phytotoxin (thaxtomin A), which is induced in the presence of cellobiose and suberin, S. ipomoeae produces a less-modified, phytotoxin (thaxtomin C), whose inducer has not been identified. To investigate transcriptional regulation of thaxtomin C production, we inserted a promoter involved in thaxtomin C synthesis upstream of the gusA reporter in an S. ipomoeae strain. Reporter gene expression was significantly upregulated in the presence of size-fractionated sweetpotato extract (SPE). The …

Molecular Mechanisms Of Boron Toxicity Tolerance In Plants, Guannan Wang

LSU Doctoral Dissertations

Boron toxicity is a worldwide agricultural problem that limits crop productivity and quality. However, our understanding on the genetic responses and adaption mechanisms to boron toxicity in plants is very limited. To address this gap in our knowledge, I compared boron stress-sensitive model, Arabidopsis thaliana and its stress-adapted relative Schrenkiella parvula to study how plants respond and adapt to excess boron at physiological, genomic, transcriptomic, and metabolic levels.

The overall project goal involved integration of multi-omics datasets to develop genome to phenome interpretations. To achieve this, I developed a python package, GOMCL, to facilitate the extraction of biologically meaningful information …

Floodplain Forest Regeneration Dynamics In The Lower Mississippi River Alluvial Valley, Whitney Anne Kroschel

LSU Doctoral Dissertations

Floodplain forest species diversity is driven, in part, by variation in disturbance regime. Flood patterns create heterogeneity in microsite quality from small differences in elevation across a floodplain which, in turn, influence flood timing and duration. Differences in species’ regeneration niches in relation to hydrologic patterns can account for long-term coexistence of various species. In the past century floodplain forests have exhibited a wide range of changes in stand development and species composition as a result of altered hydrology in rivers and floodplains. I evaluated the role of regeneration in floodplain forest systems of the Lower Mississippi River Alluvial Valley …

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 …