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  • ItemOpen Access
    Population genetics prior to biological control: Ceutorhynchus weevils proposed for managing garlic mustard
    (Colorado State University. Libraries, 2009) Rauth, Steven J., author; Hufbauer, Ruth, advisor
    I studied the population genetic structure of three weevil species, Ceutorhynchus alliariae, C. roberti, and C. scrobicollis, being considered for the biological control of garlic mustard, Alliaria petiolata, in North America. My first objective was to develop a polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) assay which could be used to identify the morphologically indistinguishable larvae. This assay was developed for use in the analysis of population genetic structure of the three species and to aid scientists in evaluating host-specificity test results where larval development was incomplete or adults failed to emerge. The resulting assay provides a fast and inexpensive means of identifying otherwise indistinguishable larvae. My second objective was to study the population genetic structure of C. scrobicollis, to evaluate whether the areas where individuals were being collected for host-specificity testing consisted of one or more populations, to estimate the numbers of individuals needed during host-specificity testing and later introduction to adequately represent the diversity of the population, and to evaluate dispersal potential. Results suggest that C. scrobicollis in the area of Berlin, Germany constitute a network of subpopulations with low but significant differentiation among sites and movement of individuals between sites. I estimated that the number of individuals that would need to be sampled to capture 90% or 99% of the genetic diversity in the Berlin area was 10 and 27, respectively. The estimated average dispersal distance based on assignment tests for C. scrobicollis was 28 km. My third objective was to compare the differences in population genetic structure between C. alliariae and C. roberti to determine whether differences in genetic diversity or dispersal potential might aid in prioritizing one species over the other. These two species have similar life histories, distributions, and effects on garlic mustard. Results showed that, over a comparable region in central Europe, total gene diversity was significantly higher in C. roberti, though the difference between the two species was relatively small. Assignment tests suggest there is substantial gene flow among sites for both species. Overall, the results were similar for both species, and I recommend prioritizing based on biological or methodological attributes.
  • ItemOpen Access
    Molecular genetics of glyphosate resistance in Palmer amaranth (Amaranthus palmeri L.)
    (Colorado State University. Libraries, 2009) Gaines, Todd A., author; Westra, Philip, advisor; Leach, Jan, advisor
    Glyphosate resistant Palmer amaranth populations were identified in Georgia in 2004. Studies were undertaken to characterize inheritance, the molecular basis of resistance, and the potential for gene transfer to related Amaranthus species. Dose response results support rejecting a monogenic inheritance hypothesis in favor of an alternative polygenic, additive inheritance model. Apomixis in genetic populations used for inheritance studies is probably occurring and makes interpretation of inheritance difficult. Glyphosate resistance in Palmer amaranth appears to be incompletely dominant and may be polygenic. No target site mutations known to confer resistance were identified in resistant alleles of the 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) gene, the target of glyphosate. Estimation of gene copy numbers of EPSPS relative to acetolactate synthase (ALS) in gDNA by quantitative PCR (qPCR) suggested that resistant plant genomes contain 64 to 128 times more copies of EPSPS than susceptible plants. qPCR on cDNA revealed that EPSPS was expressed approximately 35 times higher in resistant plants. Elevated EPSPS copy number is heritable and correlates with expression level and resistance in F2 populations. The molecular basis of resistance is likely due to increased production of EPSPS due to gene amplification. This is the first documented occurrence of EPSPS gene amplification in a weed population under glyphosate selection pressure. The risk of resistance gene transfer was measured with field studies and hand crosses with A. hybridus, A. retroflexus, A. powellii, A. spinosus, and A. tuberculatus. Glyphosate application (0.4 kg ha-1) was used to screen for resistant progeny from the crosses. Hybridization with A. spinosus occurred in both years of the field study and in hand crosses, with average frequency ranging from <0.01% to 1.4%. Hybrids with A. spinosus were either monoecious or dioecious. Monoecious plants produced seed through self-pollination, and the F2 progeny were segregating for resistance. Hybridization occurred in the 2007 field study with A. hybridus (<0.01%) and A. tuberculatus (0.08% and 0.19% for two accessions), all of the hybrid plants were dioecious, and none produced seed. The highest risk for glyphosate resistance gene transfer from A. palmeri is to A. spinosus.
  • ItemOpen Access
    Iris yellow spot virus in Colorado onions: a survey of its spatial distribution and techniques to manage the pest
    (Colorado State University. Libraries, 2007) Fichtner, Scott M., author; Schwartz, Howard F., advisor; Hill, Joe, advisor
    The Iris yellow spot virus (IYSV) is a new, and at times devastating pathogen of alliums throughout the U.S. as well as many other countries. Since its discovery in Colorado in 2001, IYSV has been identified in nearly all of the major onion producing regions within the state. The severity of this virus disease appears to fluctuate from one year to the next but incidence continues to increase with newly infested fields identified each year. With the number of outbreaks on the rise and the inadequacy of current control strategies, new management techniques as well as novel chemistry pesticides have become a major focus for the management of this virus disease and its thrips vector. Our trials demonstrated the use of reflective materials such as straw or silver reflective mulch can result in a reduction in thrips populations by as much as 69% on onions and a reduction of nearly 9% in IYSV disease incidence. Additionally, Entrust (Spinosad) and Aza-Direct (Neem extract) were found to work as well as or better than conventional materials such as Warrior (Pyrethroid) and Lannate (Carbamate). To better understand the epidemiology of the IYSV pathogen, we also conducted an extensive survey at several locations along the Colorado Front Range and Western Slope. In our surveys, we collected information including thrips populations and incidence of IYSV using 0.2 ha grids developed using mapping software (MapInfo) creating several randomly chosen plots in each field. With data collected on several sampling dates, we attempted to identify a spatial correlation of within field spread of the virus during the growing season. The levels of positive spatial autocorrelation from our survey locations were minimal, this leads us to believe that secondary outbreaks of the disease are occurring in a random fashion across the field.
  • ItemOpen Access
    Functional characterization of germin family genes contributing to broad-spectrum, quantitative disease resistance in rice
    (Colorado State University. Libraries, 2009) Davidson, Rebecca M., author; Leach, Jan E., advisor
    Quantitative trait loci (QTL) are predicted to confer broad-spectrum and durable disease resistance. Application of disease resistance QTL in crop improvement programs has been hindered because we lack an understanding of (1) the genes contributing to the QTL-governed phenotype and (2) why certain alleles are more effective than others in conferring resistance. In this study, QTL-associated genes in the germin protein family, germin-like proteins (GLP) and oxalate oxidases (OXO), were identified in the rice genome and their functions were tested. Paralogous multi-gene families underlie the physical QTL regions, with twelve OsGLP members on chromosome (chr) 8 and four OsOXO members on chr 3. Based on shared motifs in 5' regulatory regions and/or protein sequence similarities to cereal orthologues, rice OsGLP genes belong to two germin subfamily groups (GER3 and GER4), and OsOXOs belong to the GER1 group. Conserved sequences for each gene family were used in RNA-interference gene silencing experiments. As more OsGLP genes were silenced, the more susceptible the plants were to two distinct fungal pathogens, Magnaporthe oryzae (Mo) and Rhizoctonia solani (Rs). Similarly, OsOXO-RNAi plants showed enhanced susceptibility to Mo, Rs and the broad host range pathogen, Sclerotinia sclerotiorum. OsGLP alleles were compared in resistant (+chr8 QTL) and susceptible (-chr8 QTL) parental rice lines. Cultivar-specific combinations of OsGLP genes were constitutively expressed and transiently induced by both wounding and Mo infection. In agreement with the silencing data, expression profiles suggest that GER4 subfamily members are involved in rice defense response. Transient induction occurred before fungal penetration of the plant cuticle, and differential expression between resistant and susceptible cultivars correlated with differential hydrogen peroxide accumulation after fungal infection and abiotic stresses. Gene silencing data confirms the roles of OsGLP and OsOXO as contributors to broad-spectrum, basal disease resistance in rice. Studies of allelic diversity among rice varieties suggest that regulation of OsGLPs may explain the effectiveness of resistant alleles compared to susceptible. Germin family proteins are encoded by developmentally regulated gene families in rice and across plant taxa. The germin subfamily members studied here have acquired functions in broad-spectrum defense responses and are important loci for crop improvement.
  • ItemOpen Access
    Dispersal of an invasive tumbleweed
    (Colorado State University. Libraries, 2007) Baker, Dirk V., author; Beck, K. George, advisor
    Dispersal is of critical importance for species conservation and reducing the spread of invasive species. I investigated the dispersal of the invasive tumbleweed, Centaurea diffusa. Tumbleweed dispersal is composed of three components; the plant stem must break free; wind must be sufficient to move plants; and seed must be retained in the plant with time and distance. Dispersal peaks were variable in space and time. Dispersal events correlated with wind gusts and variability in temperature. However, 18 and 78% of plants tumbled over 2 years at sites near Larkspur and Superior, CO, respectively. Weather did not fully explain the differences in dispersal magnitude. Raising plants from the sites in common garden revealed that Larkspur plants required 57% greater force to break than plants from the Superior site. In addition, plants under dry post-senescence soil conditions required four to six times greater force to break compared to plants under moderate to high soil moisture. Based on wind tunnel measurements, wind velocities necessary to break C diffusa stems ranged from 16 to 37 m/s. I developed a GIS-based model for the movement patterns of this plant based on topography, vegetation and wind patterns. Such modeling could provide information to help reduce the spread of this important invasive weed. However, model accuracy needs to be improved before it will be applicable to management. I conducted field and wind tunnel experiments to estimate seed dispersal with time and distance. The 95 percentile confidence limits for the half-life of seed retention in non-dispersed plants were 3 and 14 weeks suggesting that even late-dispersing plants have strong potential for longer distance dispersal of seeds. Seeds were commonly retained in plants for distances of 200 to 400 m and one still had seed in it after traveling over 1 km. Seed dispersal with distance seems linear, though exponential decay may better represent extreme dispersal events. Both models substantially overpredicted dispersal distances for field data collected during a drought year in the presence of biocontrol insects. This research has substantially increased knowledge of the dispersal of this plant and has highlighted future research needs.
  • ItemEmbargo
    Involvement of CYP72A219 in herbicide-resistant Palmer amaranth and the role of P450 reductase in the mechanism of metabolic resistance
    (Colorado State University. Libraries, 2023) Rigon, Carlos A. G., author; Gaines, Todd A., advisor; Dayan, Franck E., advisor; Beffa, Roland, committee member; Peebles, Christie, committee member
    Herbicide resistance in weeds poses a major challenge to modern agriculture worldwide, impacting effective weed control strategies. Metabolic resistance stands out as the major and more complex resistance mechanism due to its ability to metabolize a wide range of herbicides within weed species. Metabolic resistance involves herbicide metabolism through three key phases: activation, conjugation, and sequestration. These phases involve the action of important enzymes such as cytochrome P450 monooxygenases, glutathione S-transferases, and ABC transporters. Metabolic resistance mechanisms have gained prominence in the past decade, posing significant challenges to sustainable agriculture and weed management practices. Amaranthus palmeri (Palmer amaranth) one of the most troublesome weeds globally has evolved metabolic resistance to HPPD inhibitor tembotrione. Understanding and addressing the mechanism are crucial for developing effective strategies to combat herbicide resistance and ensure global crop production. In the present study, four upregulated P450 genes were identified in HPPD-resistant Palmer amaranth from Nebraska (NER), a troublesome weed species. Among these genes, CYP72A219_4284 demonstrated the ability to deactivate the herbicide tembotrione in a heterologous system. This gene was also upregulated in metabolic HPPD-resistant Palmer amaranth plants from different fields across the United States, indicating its involvement in conferring herbicide resistance. Our study also investigated the regulation of these resistance genes, including the promoter sequences and transcription factors involved. Additionally, quantitative trait loci associated with herbicide resistance were identified. This work represents the first identification and validation of genes responsible for herbicide metabolism in Palmer amaranth. Validation of the metabolic resistant gene and the exploration of regulatory mechanisms contribute to a better understanding of metabolic herbicide resistance in weeds, facilitating the development of effective weed management strategies. Cytochrome P450 reductase (CPR), an essential enzyme localized in the endoplasmic reticulum, provides electrons for P450 enzymes during monooxygenase reactions. The transfer of electrons from NADPH to the P450 active site occurs through a complex CPR:P450 interaction. Despite the numerous P450 genes in plant genomes, CPR genes are limited, typically consisting of two or three copies. In Arabidopsis, the two CPR genes, ATR1 and ATR2, have distinct roles in primary and inducible metabolism, respectively. Our study investigated the function of ATR1 and ATR2 in transgenic Arabidopsis plants overexpressing the CYP81A12, which is known to metabolize a wide range of herbicides. The hypothesis was that silencing these ATR1 or ATR2 genes would lead to a reduction of P450 activity involved in herbicide metabolism. ATR1 predominantly transfers electrons to CYP81A12, as knocking down ATR1 led to a significant reduction in herbicide resistance. Knockouts of the ATR2 gene also resulted in decreased herbicide resistance, although the effect was less pronounced. Variation in the number and function of CPR genes among different weed species suggests diverse genetic pressures and potential targets for herbicide resistance management. Inhibition of CPR activity could be a promising approach to restore herbicide effectiveness against metabolic herbicide-resistant weeds. This is the first study to our knowledge that explores the involvement of CPR genes in herbicide resistance in weeds, providing valuable insights into their crucial role. The findings significantly advance our understanding of the mechanisms underlying CPR-mediated herbicide resistance and offer potential targets for the development of effective weed management strategies.
  • ItemOpen Access
    Developing integrated pest management tactics for alfalfa mosaic virus and its aphid vector in chile peppers
    (Colorado State University. Libraries, 2023) Janecek, Taylor, author; Szczepaniec, Adrianna, advisor; Nachappa, Punya, committee member; Uchanski, Mark, committee member
    Alfalfa mosaic virus (AMV, Bromoviridae: Alfamovirus) is a virus transmitted to plants by aphids in a non-persistent manner. The virus was first identified in chile peppers Capsicum annuum L. (Solanales: Solanaceae) in Southern Colorado in 2019. The goal of this research was to explore management strategies to suppress the virus given its devastating impact on the yield and quality of chile peppers. The objectives were to: 1) determine whether chile peppers have innate resistance to AMV, 2) test the effectiveness of host plant resistance and planting date modifications to suppress the virus in the field, 3) determine whether AMV is seed transmissible, and 4) survey abundance and diversity of aphids (Hemiptera: Aphididae) that likely transmit AMV in the system. In the greenhouse experiment, I found significant differences among varieties of chile peppers in the severity of AMV symptoms and identified a variety suitable for a field experiment. In the field, I found that the susceptible variety, Joe Parker, which tended to have high AMV symptoms in the greenhouse, was also highly susceptible to AMV in the field. Conversely, Mira Sol, which appeared to have resistance to the virus in the greenhouse screening assay had low incidence of AMV symptoms and low AMV titers in the field as well. Planting date also played an important role in symptom severity, where late planted peppers (mid-June) had significantly lower severity of AMV symptoms than peppers planted at conventional and early planting dates (the middle and end of May). Despite this, the yield and quality of peppers planted early was significantly greater than that of peppers planted later in the season. In addition, there was evidence of seed transmission of AMV in chile peppers, with 10% for Mira Sol and 2% for Joe Parker, from seeds collected from infected peppers had AMV. Lastly, I found high diversity of aphid species within my experimental plots (14-16 species) and lower diversity in nearby alfalfa fields (4-5 species). Moreover, severity and titers of AMV were positively correlated with earlier planting date, which was likely related to higher aphid densities early in the season. This research contributed to formulating integrated tactics that chile pepper producers can implement in their production to suppress the impact of AMV on the crop. Finally, this is the first report of AMV transmission through seed in peppers and is the first study describing this pathosystems in Colorado.
  • ItemEmbargo
    Sweet surprise: the search for genes conferring beet curly top virus resistance
    (Colorado State University. Libraries, 2023) Withycombe, Jordan, author; Nachappa, Punya, advisor; Nalam, Vamsi, committee member; Nishimura, Marc, committee member; Dorn, Kevin, committee member
    Sugar beets (Beta vulgaris L.) are grown across the western United States and suffer economic loss annually to curly top disease. Curly top disease is caused by the beet curly top virus (BCTV) and is spread by the only known insect vector the beet leafhopper, Circulifer tenellus Baker (BLH). Current management strategies for BCTV include chemical control using neonicotinoid seed treatments and foliar insecticidal sprays, as well as the use of BCTV-resistant sugar beet varieties. However, the underlying genetic mechanism surrounding resistance in sugar beet is unknown. The overarching goal of this study was to identify the mechanism of resistance in sugar beet to BCTV and identify potential genes conferring resistance. The objectives for this study were: 1) classify the nature of BCTV resistance in a resistant (EL10) and susceptible (FC709-2) genotype of sugar beet using host suitability and host preference insect assays, as well as assess viral load within each genotype and 2) characterize the transcriptional response to BCTV infection using RNA-sequencing. To classify the nature of BCTV resistance in each genotype of sugar beet, host suitability and preference assays were conducted using virus infected and uninfected BLH. In host suitability assays, the percentage of surviving BLH adults and the number of nymphs produced when reared on a single plant of either genotype was determined over a 3-week period. There was no difference in adult survival, or the number of nymphs produced on either genotype for the virus infected or uninfected leafhoppers. Host preference assays were used to assess settling behavior of BLH over time when given a choice between the two genotypes. It was concluded that virus infected leafhoppers had a clear choice to settle on the susceptible genotype at all timepoints after 4 hours, while uninfected leafhoppers did not make as strong of a settling choice. Average viral load for each genotype across three timepoints was estimated using qPCR. The results showed that the average viral load increased in each genotype over time, yet there was no difference in the average viral load between the genotypes at any individual timepoint. The global transcriptional response to BCTV infection over time for a resistant and susceptible genotype of sugar beet was conducted using RNA-sequencing technology. Mock-inoculated and BCTV-inoculated plants from each genotype were sampled on day 1, 7 or 14 post inoculation resulting in the preparation of 36 mRNA sequencing libraries. Comparison between mock-inoculated and BCTV-inoculated plants of each genotype and timepoint were conducted separately to generate six list of differentially expressed transcripts (DETs). Each transcript was annotated with a description and further classified for its role in the plant biological, cellular or molecular processes. The results showed that both genotypes of sugar beet had a dynamic response to BCTV infection over time, although there was minimal overlap between the responses to one another. EL10, the resistant genotype, had DETs associated with phytohormone production including jasmonic acid and abscisic acid, along with proteins linked to stress reduction and the downregulation of plant primary metabolic processes. In contrast FC709-2, the susceptible genotype, was found to produce opposing phytohormones like salicylic acid and auxins, as well as the production of volatile organic compounds and an increase of primary plant metabolic processes. These opposing responses shed light on the differences in the transcriptional response of a resistant and susceptible genotype of sugar beet. Understanding and classifying the mechanisms of resistance or susceptibility to BCTV infection in sugar beet is beneficial to researchers and plant breeders as it provides a basis for further exploration of the host plant-virus-vector interactions.
  • ItemEmbargo
    Integrated weed management: insights from a weed resistance survey and non-chemical weed seed control in the Central Great Plains
    (Colorado State University. Libraries, 2023) Simões Araujo, André Lucas, author; Gaines, Todd, advisor; Dayan, Franck, committee member; Fonte, Steven, committee member
    With the impending release of genetically engineered sugar beet varieties with resistance to glyphosate, dicamba, and glufosinate, significant changes are expected in weed management practices, particularly with regards to in-crop weed control. Glyphosate is used during fallow and in-crop periods, while dicamba is commonly employed in fallow applications, specifically targeting glyphosate-resistant weed species. This study provides insights into the resistance status and frequency of resistance in problematic weed species to the three active ingredients in sugar beet systems across Colorado, Nebraska, and Wyoming. While numerous studies have highlighted the widespread prevalence of glyphosate-resistant kochia and Palmer amaranth across the United States, there is limited research focusing on these species within the context of a sugar beet system. Additionally, our findings reveal the first occurrence of glyphosate-resistant and dicamba-resistant Palmer amaranth populations in Colorado, and dicamba-resistant kochia populations within a sugar beet system. Furthermore, we report that all dicamba-resistant kochia populations tested in Colorado lack a known target-site resistance mechanism, suggesting the involvement of a novel resistance mechanism. Surveys assessing glufosinate resistance in the sugar beet system have not been conducted until now, and we provide valuable baseline information on the resistance frequency for this herbicide prior to an anticipated increase in glufosinate use. To address the widespread issue of herbicide resistance in various crop systems, it is crucial to adopt alternative strategies that mitigate resistance evolution and maintain the long-term effectiveness of available herbicides. One promising approach is chaff lining, a harvest weed seed control method that has gained popularity in Australia due to its effectiveness in reducing populations of herbicide-resistant ryegrass, especially when combined with other weed control methods. However, the efficacy of chaff lining may be influenced by several factors, including crop and environmental factors, as reported in Australian literature. Scientific studies assessing the applicability and effectiveness of chaff lining in the United States are limited. Recognizing this research gap and aiming to explore the potential of chaff lining, our study investigated its applicability in field settings within the Central Great Plains region of the United States. Through our research, we provide insights into chaff lining efficacy of and highlight the potential inconsistencies that may arise in suppressing weed seeds using this method. Notably, we demonstrate that various factors, including location and environmental conditions, may be involved and impact the effectiveness of chaff lining as a weed management strategy. These findings underscore the importance of integrating chaff lining with other weed management methods to achieve effective and sustainable weed control. Chaff lining, like any other weed management strategy, should not be solely relied upon. Instead, it should be implemented as part of an integrated approach to ensure its long-term effectiveness.
  • ItemEmbargo
    Uncoupling plant growth and defense through phytohormone crosstalk modification
    (Colorado State University. Libraries, 2023) Johnston, Grace Allen, author; Argueso, Cris, advisor; Leach, Jan, committee member; Prasad, Ashok, committee member
    Phytohormones are essential regulators of development and response to biotic and abiotic stresses. Activation of the plant immune system by pathogen attack often results in changes in plant growth, frequently leading to smaller plants with reduced seed set. Previously, we discovered that cytokinin (CK), a hormone known for its role in the regulation of cell division and plant growth, also has an important role in the activation of defense against pathogens through a synergistic interaction with the defense hormone salicylic acid (SA). Here, we address whether these two phytohormones also regulate the negative effect of immune activation on plant growth. Differential gene expression analysis and physiological assays were used to characterize the crosstalk between CK and SA in growth and defense in Arabidopsis thaliana plants with altered states of immunity. We show that the interplay between the phytohormones CK and SA regulates both defense responses to pathogens and plant development. Endogenous levels of these two hormones were modulated in the snc1 ckx3 ckx5 (s35) triple mutant. The three mutations result in increased CK and SA content simultaneously and yields a novel reproductive growth phenotype. When challenged with pathogens from diverse lifestyles, the s35 mutant conserves an autoimmune phenotype. Transcriptome analysis of s35 reproductive tissue reveals differential regulation of genes associated with nitrogen response and regulation of redox status. Our data suggests that the increased content of both CK and SA hormones contributes to a rebalancing of redox homeostasis and perception of nutrient availability within the shoot apical meristem (SAM), resulting in the uncoupling of reproductive growth and pathogen defense. Further experimentation and investigation into the mechanistic interactions mediating the balance between plant growth and defense could lead to implementation of phytohormone crosstalk engineering to target specific advancements in crop species.
  • ItemOpen Access
    Phytoalexin deficient4 (PAD4): a plant defense regulatory gene with distinct alternative splicing patterns in tomato (Solanum lycopersicum) and soybean (Glycine max)
    (Colorado State University. Libraries, 2023) Schmidt, Rebecca, author; Nalam, Vamsi, advisor; Argueso, Cristiana, committee member; Reddy, Anireddy, committee member
    Alternative splicing is an important post-transcriptional regulatory mechanism that contributes to a plant's ability to perceive and respond to a variety of biotic and abiotic stressors. Alternative splicing has a documented role in plant immunity, as many R genes, which are important for plant defense against specialized pathogens, undergo alternative splicing in response to pathogen perception. Despite this, the role of alternative splicing in other components of plant defense responses is not well documented. As transcriptome data diversify to include more species and conditions, the extent of alternative splicing in plants has become apparent. PHYTOALEXIN DEFICIENT4 (PAD4), plays an integral role in plant defense signaling to biotic stressors, and in regulating responses to abiotic stresses. PAD4 undergoes alternative splicing in Soybean (Glycine max). Additionally, the expression pattern of Glycine max PAD4, GmPAD4, and its splice variant GmPAD4-AS1 are further characterized in early growth stages. We hypothesize PAD4 produces full-length and alternatively spliced transcripts in multiple species, and that PAD4 gene structure may influence the occurrence of alternatively spliced transcripts. Here we characterize alternative splicing of PAD4 in tomato (Solanum lycopersicum), identifying two splice variants. We also investigate the conservation of PAD4 intron-exon structure conservation across diverse species. PAD4 expression patterns are characterized using available expression data.
  • ItemOpen Access
    Factors affecting potato early dying in the San Luis Valley, Colorado
    (Colorado State University. Libraries, 1994) Davidson, Robert Day, author; Harrison, Monty D., committee member; Knutson, Kenneth W., committee member; McIntyre, Gary, committee member; Schwartz, Howard, committee member
    A three year comparison of Russet Burbank potatoes field grown in microplots containing combinations of Verticillium (V), Erwinia carotovora subsp. carotovora (Ecc) and E. c. subsp. atroseptica (Eca) inoculated into the seed and, in the case of Ecc, also applied in the irrigation water was conducted. Three levels of irrigation were used for all treatments. Verticillium appeared to have minimal impact. Plant stand, height and tuber numbers were not significantly different among treatments. Verticillium wilt or potato early dying (PED) progress was, in general, significantly greater than normal maturity in controls. Yield was significantly depressed in only one of three years. In the two warmest years, yields increased as irrigation increased. In the coolest year, the reverse was true with yields increasing as irrigation decreased. Greenhouse studies completed in 1989 showed that air temperature can play a major role in PED symptom development. Specialized chambers were held at three different air temperatures 15, 25 and 30°C with treatments similar to those used in the field studies. PED symptom progression was fastest under the highest temperature (30°C), but did not reach the same level of severity as found under lower temperatures. PED was greatest under the 25°C temperature, while almost non-existent at 15°C. Soil fumigation with BusanR resulted in reductions in Verticillium microsclerotial counts which were maintained for at least two further growing seasons. However, unfumigated soil also showed similar reductions in microsclerotial counts during the same time period. Ecc and Eca appeared to be the primary pathogens causing disease in the PED complex in the San Luis Valley, while V. dahliae appeared to have a secondary role. Synergistic V + Erwinia interactions were found. Progress of PED in V + Erwinia seed treatments was similar to or sometimes significantly greater than PED progress in plants exposed to either Erwinia or Verticillium alone. Yields were significantly lower than the control or either pathogen alone in three of the V + Erwinia seed treatments. Under pathogen combination treatments there was an obvious trend toward reduced yields and, as irrigation increased, toward increased PED severity, disease progress and yield loss. Erwinia carotovora treatments had significant reductions in stand in two of three years with Erwinia seed treatments, but not when Ecc was introduced through irrigation water. Overall, as irrigation and Erwinia inoculum density increased, stand loss increased. Tuber numbers and yields were, in general, depressed significantly under Erwinia seed treatments. In 1990 the high Ecc irrigation treatment under optimum moisture also significantly decreased yields. Erwinia infection of daughter tubers was greatest in the two cooler seasons. Overall, the higher the inoculum level used or the greater the water stress, the higher the infection rate.
  • ItemOpen Access
    Soil microbial communities associated with forest root diseases and Rocky Mountain forests
    (Colorado State University. Libraries, 2022) Lalande, Bradley, author; Stewart, Jane, advisor; Stromberger, Mary, committee member; Tinkham, Wade, committee member; Trivedi, Pankaj, committee member
    To view the abstract, please see the full text of the document.
  • ItemOpen Access
    Developing integrated pest management (IPM) strategies for hemp russet mite (Aculops cannabicola Farkas) on hemp (Cannabis sativa L.)
    (Colorado State University. Libraries, 2022) Hayes, Christopher, author; Nachappa, Punya, advisor; Cranshaw, Whitney, advisor; Prenni, Jessica, committee member
    Cannabis sativa L. is a plant that is rapidly becoming a crop of global agricultural importance. However, because of the historical peculiar regulatory status of this crop little has been developed on the pests and pest management needs of the crop. Among the more serious pests that have become established with this plant is hemp russet mite (HRM) Aculops cannabicola Farkas (Acari: Eriophyidae). In order to assess the efficacy of various IPM approaches to mitigating HRM infestations, a series of field and lab experiments were conducted including: 1) evaluation of the effects of sprays of sulfur on control of hemp russet mite, yield, and cannabinoid produduction; 2) evaluation of the efficacy of field release of the phytoseiid mites Amblyseius andersoni, A. swirskii, Neoseiulus fallacis, and N. californicus on HRM-infested hemp plants; and 3) evaluation of hot water immersion as a potential disinfestation method for HRM-infested cuttings used in propagation. The results of the sulfur sprays in field trials showed excellent ability to suppress HRM by up to 98%. Yields of treated plants improved by up to 33% and there was a further increase in the percentage of phytocannabinoids by up to 45% relative to untreated plants. Greatest effects were seen in all trials with plants receiving two applications, one during the vegetative period in July and the second at the initiation of flower production in August. Mass releases of N. fallacis and A. swirskii, but not N. californicus and A. amblysieus, did produce a significant reduction in HRM populations, but no treatments significantly affected yield or percentage of phytocannabinoids, relative to untreated plants. No reproduction was observed of any of the released mites on HRM-infested plants. Immersion treatments to disinfest cuttings included use of a water bath at temperatures of 106°F or 109°F for 10 or 15 minutes, and dips in room temperature surfactant solution of Dr. Bonner's Pure-Castile lavender soap at 1.0% and 0.1% concentrations. All treatments were able to cause significant reduction of HRM on infested hemp cuttings, although none caused complete elimination. No phytotoxicity, as evidenced by effects on subsequent rooting, were observed with any treatment. This study provides novel effective approaches to mitigating HRM at multiple stages in hemp production operations. Outcomes of this research may provide hemp producers and other stakeholders with key pest management strategies needed to produce hemp plants that are free of HRM.
  • ItemOpen Access
    The role of chemical canopy sprays and irrigation methods on the incidence of the perennial canker, Cytospora plurivora in western Colorado peach orchards
    (Colorado State University. Libraries, 2022) Wright, Sean, author; Stewart, Jane E., advisor; Charkowski, Amy, committee member; Uchanski, Mark, committee member
    Cytospora plurivora is a secondary pathogen that has reached near epidemic levels in peach orchards on the western slope of Colorado. C. plurivora is responsible for Cytospora canker disease and is a limiting factor in peach production in the Grand Valley. Peach growers have limited management methods available to combat this disease, which prompted an investigation into irrigation practices as well as prophylactic chemical sprays following freeze events. In late 2020, the western slope received a freeze event that caused severe damage to peach shoots, buds, and twigs. Freeze damage provides infection courts within tree tissues that C. plurivora can infect. This freeze event prompted growers to apply prophylactic chemical sprays of Captan, lime sulfur, and lime sulfur with the addition of NuFilm. An efficacy threshold of three-months post chemical spray was determined for both Captan and lime sulfur treatments. Lime sulfur with the addition of NuFilm showed a loss of efficacy at two-months post spray. Additionally, an investigation into the movement of C. plurivora conidia under differing irrigation techniques was conducted. Both drip and micro-sprinkler treatments had positive detections for C. plurivora over the course of the study. In these studies, conidia traveled much greater distances than previously shown, traveling up to 135m from the closest canker. Understanding how chemical canopy sprays and different watering practices affect the incidence of Cytospora canker disease will assist in preserving the peach industry on the western slope of Colorado.
  • ItemOpen Access
    TALE-bound QTL: a computational investigation of bacterial effector association with resistance quantitative trait loci in Oryza sativa
    (Colorado State University. Libraries, 2022) Sharkey, Jacob Emmett, author; Leach, Jan E., advisor; Huerta, Alejandra I., committee member; Nishimura, Marc, committee member; Roberts, Robyn, committee member
    Durable resistance to Xanthomonas oryzae pathovars oryzae (Xoo) and oryzicola (Xoc), which cause bacterial blight and bacterial leaf streak, respectively, is highly sought after in rice (Oryza sativa) due to the pathogens ability to impact maximum attainable yields. Regions of the rice genome associated with quantitative resistance to multiple strains of Xoo and Xoc, known as quantitative trait loci (QTL), were previously identified using a multi-parent advanced generation intercross (MAGIC) rice population and a combination of genome wide association studies and interval mapping. These QTL have been associated with decreased lesion lengths by Xoc and Xoo on rice. What remains unknown is the molecular basis for the induction of genes under these QTL during pathogen infection. Considering our biological question "what is the molecular basis for regulation of resistance QTL associated with Xoo and Xoc?", we predicted that part of the answer could be found by investigating the bacteria's direct interaction with the O. sativa genome. Upon infection, Xoo and Xoc injects the host with DNA-binding TALE (transcription activator-like effector) proteins. These effectors, when bound to their target plant gene promoter, induce gene transcription. We hypothesize that differential interactions of TALE with promoters of rice genes under the QTL lead to the resistant/susceptible phenotypes exhibited across varieties. To test this, we designed a pipeline that predicts TALE-regulated candidate genes involved in quantitative resistance. This pipeline identifies genes that meet three criteria: (1) the presence of a binding site for an X. oryzae TALE in the gene's promoter, a strong correlation between binding site presence, and disease phenotypes and overlap of the gene with a resistance QTL. We used this pipeline with genomic and phenotypic data for the eight MAGIC founders to identify candidate genes involved in resistance against seven Xoo and Xoc strains. Candidate genes identified include ones encoding a patatin-like phospholipase and multiple NB-ARC containing proteins such as the Mla1 protein. Here, we exploit the abundant genomic data for the rice-X. oryzae systems and the ability to predict direct associations between bacterial proteins and plant genomes, to propose a method that could streamline the identification of genes involved in quantitative resistance to TALE- harboring Xanthomonas.
  • ItemOpen Access
    Pavement, pests, & parasitoids, oh my! Elm herbivores and their natural enemies in the urban forest
    (Colorado State University. Libraries, 2022) Buenrostro, Jacqueline, author; Hufbauer, Ruth, advisor; Cranshaw, Whitney, committee member; Redmond, Miranda, committee member; Stewart, Jane, committee member
    Urban areas are the fastest growing habitat type in the world, and an increasing proportion of the United States and global population lives in urban areas. Urban forests provide essential ecosystem services to rapidly expanding urban populations, but their health is threatened by damaging herbivory from non-native, invasive insects. To address this problem, my masters research investigated two critical questions that limit our ability to sustainably manage invasive insects in urban forest ecosystems: (1) How do urban environments impact the density of invasive herbivores in the urban forest? and (2) Are predator and parasitoid natural enemies present, and, if so, what is the level of parasitism? I investigated these questions in the context of the elm-herbivore study system, analyzing a globally distributed host tree and its complex of invasive insect pests in Colorado, USA. In my first chapter, I address the first question and explore how a variety of environmental factors that vary across urban habitats influence the density of several invasive insects. Specifically, I evaluate how vegetational complexity, distance to buildings, impervious surface, canopy temperature, host availability, and density of co-occurring herbivores impact three invasive pests of elm trees: the elm leaf beetle Xanthogaleruca luteola Müller (Coleoptera: Chrysomelidae), the European elm flea weevil Orchestes steppensis Korotyaev (Coleoptera: Curculionidae), and the elm leafminer Fenusa ulmi Sundevall (Hymenoptera: Tenthredinidae). I found that insect responses to these factors were species-specific, and all environmental factors were associated with density of at least one pest species except for distance to buildings. Elm leafminer density decreased with higher temperatures and was influenced by an interaction between vegetational complexity and impervious surface. Elm flea weevil density increased with greater host availability, and elm leaf beetle density increased with higher temperatures. Both elm leaf beetle and elm flea weevil density decreased with greater leafminer density, suggesting that insect density is mediated by species interactions. Results of this study can be used to inform future tree planting efforts through the selection of "safe sites", or locations where trees will be less likely to experience damaging outbreaks of insect pests. Additionally, these results can be used to strategize preventative management on trees that are located in outbreak "hotspots", or locations where environmental conditions make trees predisposed to insect outbreaks. Finally, results of this study contribute to our knowledge of the dynamic ways in which multiple invasive insects interact in urban environments. This information will be especially valuable as non-native insect introductions continue to increase into the future. In my second chapter, I narrow my focus to two historically important and particularly damaging pests of elm, the elm leaf beetle and elm flea weevil, to address the second question listed above and explore the complex of natural enemies attacking these two pests. In many areas of these insects' invaded range, outbreaks severely damage elm hosts. Natural enemies are thought to be important in regulating elm leaf beetle and elm flea weevil populations in other regions, but whether natural enemies are present in Colorado is largely unknown. As such, the aim of chapter 2 was to identify which predators and parasitoids of these pests are present in Colorado, a state with frequent pest outbreaks and where the natural enemy community is almost entirely undescribed. In June – August 2021, I identified predators through field observations and laboratory feeding trials, finding seven species of predators from six arthropod orders that fed on elm leaf beetle or elm flea weevil. Additionally, I reared 58 elm leaf beetle egg clusters, 539 elm leaf beetle larvae, and 435 elm flea weevil mines to detect parasitoids. Two parasitoids of elm leaf beetle, the egg parasitoid Oomyzus gallerucae and the larval-adult parasitoid Erynniopsis antennata, are present in Colorado, representing novel records of these species in the state. However, combined parasitism of elm leaf beetle eggs and larvae was low at <3% across the season, with parasitoids nearly absent early in the season and peak parasitism occurring in late summer. I found five families of parasitoid wasps that emerged from leaves containing weevil mines: Chalcididae, Encyrtidae, Eulophidae, Euplemidae, and Pteromalidae. Parasitoids emerged from <20% of leaves containing weevil mines with almost no parasitism early in the season. Given the low parasitism rates and few predators observed in our study, it seems unlikely that predator and parasitoid natural enemies exert effective control over elm leaf beetle and elm flea weevil in Colorado. This finding challenges the assumption that natural enemies are a driving force of elm leaf beetle and elm flea weevil control in Colorado. Additional research is needed to confirm species identifications for parasitoids of the elm flea weevil, disentangle elm leaf beetle and elm flea weevil population dynamics, and establish effective and sustainable control methods amidst frequent pest outbreaks. Together, these two research projects enhance our knowledge of what triggers outbreaks of the elm leaf beetle Xanthogaleruca luteola, the elm flea weevil Orchestes steppensis, and the elm leafminer Fenusa ulmi in urban areas while also laying the groundwork for a renewed interest in biological control of elm leaf beetle and elm flea weevil. It is my hope that this work can be applied to other invasive insect pests in urban forest ecosystems and make urban forests more resilient in an era when they are increasingly vulnerable to insect attack.
  • ItemOpen Access
    Russian wheat aphid, Diuraphis noxia (Kurdjomov), ecology and reproduction on five noncultivated grass hosts in high elevation environments
    (Colorado State University. Libraries, 2010) Pucherelli, Sherri F., author; Peairs, Frank B., advisor; Cranshaw, Whitney, committee member; Hansen, Neil, committee member
    Russian wheat aphid ecology, occurrence, movement, and reproduction on five noncultivated grass hosts was examined in high elevation environments. The objectives of the first study were to: 1) identify Russian wheat aphid occurrence and abundance on five common grass hosts at elevations between 1,829- 2,743 m during June-October; 2) monitor Russian wheat aphid movement and flight patterns between 1,524- 2,743 m, with the use of suction traps; 3) describe the predator and competitor assemblages encountered by the Russian wheat aphid in high elevation environments; and 4) confirm Russian wheat aphid holocycly in North America by collecting sexual forms and eggs. Weekly aphid and predator collections were made from crested wheatgrass, intermediate wheatgrass, slender wheatgrass, western wheatgrass, and foxtail barley at 23 sites, between 1,829-2,743 min the Cache La Poudre River canyon, Larimer County, Colorado. Four suction traps were installed at 1,655, 1,992, 2,206, and 2,372 m to collect alate aphids. Russian wheat aphids were collected from all five grass hosts sampled. Russian wheat aphids were most prevalent in July and most commonly collected from crested wheatgrass. Other cereal aphid species were collected, including Diuraphis frequens, Sipha elegans, Rhopalosiphum padi, Sitobion avenae, and Schizaphis graminum. Sipha elegans was the most abundant aphid collected. The most Russian wheat aphids were collected in June in the trap at 1,655 m, coinciding with peak captures in nearby wheat production. Trap captures declined with increasing elevation. Russian wheat aphid populations in the Cache La Poudre canyon are likely maintained by both immigrant aphids and from local metapopulations within the canyon. Environmental conditions in high elevation environments could prompt the production of novel biotypes. The second study determined Russian wheat aphid biotype R W A2 reproductive and development rates on the same five noncultivated grass hosts to gain information about host quality, potential refuges and sources of selection pressure. Russian wheat aphid reproductive and development rates were measured at 18-24°C, on the five grass hosts sampled in the first study, and at 24-29°C, and 13-18°C on intermediate and crested wheatgrass. The intrinsic rates of increase for all five hosts were lower than those reported for susceptible and resistant wheats. Aphids feeding on crested and intermediate wheatgrass at the 13-18°C temperature had lower fecundity, fewer nymph production days, longer generational times, and lower intrinsic rate of increase than aphids feeding at the 18-24 °C temperature regime. Poor hosts pose greater selection pressures. The five noncultivated hosts tested were poor hosts in comparison to wheat, and their greater selection pressure might promote Russian wheat aphid genetic variability.
  • ItemOpen Access
    Mountain pine beetle-caused lodgepole pine mortality from the 1980's and subsequent fire occurrence in Colorado
    (Colorado State University. Libraries, 2010) West, Daniel R., author; William Jacob, advisor; Negron, Jose, advisor; Veblen, Thomas, committee member; Rocca, Monique, committee member
    A need for understanding the interaction between post-epidemic bark beetle forest stands and subsequent fire occurrence has escalated due to recent (1999-2010) unprecedented epidemic mountain pine beetle in lodgepole pine (Pinus contorta) forests of Colorado. Outbreaks of mountain pine beetle (Dendroctonus ponderosae Hopkins) populations in the early 1980' s resulted in substantial tree mortality across Colorado and provide a means to study past outbreak areas and subsequent fire occurrence. Beetle outbreaks on the Arapaho National Forest (NF) (1980-1987) and the White River National Forest (1981-1987), delineated by the USDA Forest Service Aerial Detection Survey (ADS), indicated approximately 76,900 ha were affected, with approximately 450,000 trees killed per forest. Mountain pine beetle-caused tree mortality is generally thought to increase subsequent fire occurrence and intensity but little scientific research supports this hypothesis. Thus, my objectives were to 1) determine whether there were differences in fire occurrences between lodgepole pine forests in Colorado, impacted or not impacted by previous outbreaks of D. ponderosae and 2) determine if fire occurrences in areas with mountain pine beetle-caused lodgepole pine mortality were related to topographic attributes, ignition type, and meteorological conditions. We used historic USDA Forest Service Aerial Detection Survey maps (1980 - 1990) in conjunction with USDA Forest Service digital fire location records to look for mountain pine beetle and ignition relationships. Sixty eight maps were scanned to spatially identify D. ponderosae-caused mortality in lodgepole pine forests over the Arapaho NF and White River NF. Using a GIS, the spatial relationship between mountain pine beetle caused mortality areas and subsequent fire occurrence was identified. During the summer of 2008, 57 ignition points were field assessed on the Arapaho NF and White River NF to verify the presence of mountain pine beetle-caused mortality prior to the fire as well as confirm the location of the recorded fire. Two of the 57 ignition points had evidence of trees killed by mountain pine beetle prior to the ignition. Tests for independence of fire occurrence and mountain pine beetle-caused mortality were conducted for the Arapaho NF and White River NF. Combined human and lightning-caused fire densities did not differ (a=0.05) between areas with and without mountain pine beetle-caused mortality on the Arapaho NF, however, there were more fires in areas with mortality from the mountain pine beetle than non-impacted areas on the White River NF. Densities of lightning-caused fires alone did not differ between nonbuffered and 50 m buffered mountain pine beetle-caused mortality areas and areas outside the mortality on the Arapaho NF or White River NF. Logistic regression was used to model the probability of an ignition occurring within the area of the 1980's mountain pine beetle-caused lodgepole pine mortality on each forest. Elevation of fire occurrence was the most significant variable explaining the cooccurrence of fire with mountain pine beetle-caused mortality. Spatial autocorrelation was significant within human and lightning-caused fires but not lightning-caused fires alone. Thus, lightning-caused fires were used to eliminate the non-random nature of human-caused fires. Probability density functions were created using elevation ranges of mountain pine beetle-caused lodgepole pine mortality, lightning-caused fires prior to 1980, and elevations of fire occurrences intersecting aerially detected mountain pine beetle-caused mortality post-1980 through 2005 ( during and post-outbreaks) to identify areas of highest probability independent of one another. Maximum probabilities for the occurrence of a lightning fire in a 1980' s mountain pine beetle-caused mortality area within the Arapaho NF was between 2710 m and 2815m while on the White River NF the highest probability was between 2600 m and 2900 m. Probability density functions for a lightning fire occurring in an area with mountain pine beetle-caused mortality were applied across each National Forest using a GIS. Our analysis suggests that 1980's mountain pine beetle-caused lodgepole pine mortality has not contributed to an increase in fire frequency over the subsequent twenty five years. The variability in fire occurrence and the homogeneity of mountain pine beetle outbreak-caused mortality, past and present, between the Arapaho NF and White River NF demonstrates the limited nature of comparability of this study to other locations.
  • ItemOpen Access
    Xenobiotics translocate in aquatic plants: a case study using three aquatic herbicides
    (Colorado State University. Libraries, 2022) Ortiz, Mirella F., author; Dayan, Franck, advisor; Nissen, Scott, advisor; Bedinger, Patricia, committee member; Heilman, Mark, committee member
    When invasive aquatic weeds dominate aquatic ecosystems there are numerous negative impacts. Milfoil (Myriophyllum spp.) and hydrilla [Hydrilla verticillata (L.f.) Royle] are the most costly aquatic plants to manage in the U.S. per year. These invasive plants form extensive surface canopies that negatively affect water quality and native plant communities, and can also impact recreational uses such as swimming, fishing, and boating. Synthetic auxins, such as 2,4-dichlorophenoxyacetic acid (2,4-D), have been widely used for selective control of milfoil since 1959. Since then, several populations of hybrid watermilfoil (M. sibiricum x M. spicatum; HWM) have showed lower sensitivity to this herbicide. In 2015, a HWM population with lower sensitivity to 2,4-D was found in Idaho, USA. Using the same 2,4-D-resistant population and a known susceptible Eurasian watermilfoil (M. spicatum; EWM) population from Colorado, the mechanism of 2,4-D resistance was examined by conducting 14C-2,4-D absorption, translocation, desorption, and metabolism experiments. 2,4-D resistance in HWM is not due to non-target-site resistance as no differences in herbicide absorption, translocation, desorption and/or metabolism were identified; therefore, target-site resistance is the most likely resistance mechanism. More research is needed to identify the molecular basis for the 2,4-D-resistant trait in HWM. Herbicide combinations are widely recommended to alleviate the evolution of herbicide resistance. The aquatic herbicide endothall is often used in combination with 2,4-D for HWM management as an effective control option and a resistance management strategy, but it is still unknown how combining herbicides might impact the behavior of each herbicide. Experiments combining radiolabeled with non-radiolabeled herbicides were conducted to evaluate herbicide absorption, accumulation, and translocation from shoots to roots in HWM. Endothall accumulation was not impacted when these herbicides were applied in combination, but its translocation from shoots to roots was reduced by 50% when applied in combination with 2,4-D. When 2,4-D, was applied in combination with endothall shoot absorption increased by 80%; however, 2,4-D movement from shoots to roots was reduced from 24.8% ± 2.6 to only 3.93% ± 0.4 when in the presence of endothall. The overreliance on a single mode of action resulted in evolved fluridone resistance in hydrilla in the late 1990s. 2,4-D is not effective for hydrilla control at label rates, but the most recently registered auxinic herbicide, florpyrauxifen-benzyl, is highly active against hydrilla. Where fluridone-resistant hydrilla is present, endothall is being used in combination with florpyrauxifen-benzyl for its control. In order to test experiments combining radiolabeled and non-radiolabeled endothall and florpyrauxifen-benzyl were conducted to evaluate herbicide absorption, accumulation, and translocation in two hydrilla biotypes, monoecious (MHV) and dioecious (DHV). Herbicide accumulation in both biotypes was not impacted when these herbicides were applied in combination. Endothall translocation from shoots to roots in DHV did not appear to be impacted (alone = 18.7% ± 1.4; combination = 23.2% ± 2.2); however, endothall shoot-to-root translocation in MHV was reduced from 16.2% ± 1.3 to 2.2% ± 0.1 when applied in combination with florpyrauxifen-benzyl. Florpyrauxifen-benzyl shoot-to-root translocation was reduced by 16 and 6 times in DHV and MHV when applied in combination with endothall, respectively. These data highlight differences in herbicide behavior when herbicides are applied in combination. Future research is needed to determine if these differences negatively impact the operational effectiveness when herbicides are applied in combination. Lastly, endothall and 2,4-D have been used to control aquatic weeds for more than 60 years, and still there is very little information available about the in planta behavior of these herbicides in aquatic weed species. 2,4-D is purportedly systemic in aquatic plants based almost entirely on its behavior in terrestrial plants. It was demonstrated in this dissertation that radioactive 2,4-D and endothall can translocate from shoots to root systems; however, it was not determined if the radioactivity in the roots was parent herbicide or a metabolite(s). Therefore, the last chapter of this dissertation used multiple analytical methods to answer the question if 2,4-D and endothall are truly systemic in aquatic plants. The intact 2,4-D detected in HWM shoots was 1.31 µg g-1 dry weight (DW) and 0.11 µg g-1 DW was detected in the roots. For endothall, 1.08 and 0.12 µg g-1 DW was detected in DHV shoots and roots, respectively. We therefore conclude that 2,4-D and endothall have similar in planta behavior, with about 8-10% of absorbed intact active ingredient translocating to the roots of these aquatic plants.