Theses and Dissertations

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Open Access
Biochemical differentiation and hormonal regulation of the developing testes in Tenebrio molitor
(Colorado State University. Libraries, 1980) Alrubeai, Hussain Fadhil, author; Gorell, Thomas A. (Thomas Andrew), advisor; Seidel, George E., committee member
During differentiation, the testes of Tenebrio molitor have been found to exhibit increases in biosynthetic capacity reflected in alterations in testicular protein and RNA. This biochemical differentiation was influenced by endogenous and/or exogenous hormones. The testes underwent dramatic increases in size and weight during the prepupal stage that were continued through later developmental stages. Histological analysis revealed that the maturation process of the germ cells to produce spermatozoa proceeded from the distal end of the follicles and toward the basal region to form a "differentiation wave." Spermatozoa were found in the prepupal testes. The underlying biochemical machinery of the developmental process was found to be accelerated in manufacturing different elements for germ cell differentiation at certain stages and particularly when the endogenous level of ecdysterone rose during the late prepupal and at mid-pupal stages. Gradual increases in testicular protein and RNA content were observed during the prepupal stage. The observed increases were more dramatic for both protein and RNA content in the pupal stage. The testicular protein and RNA content reached their maximum levels between days 4 and 7 of the pupal stage as did the rate of 3H-leucine incorporation. During the adult stage, the biosynthetic processes for producing protein and RNA were apparently reduced following the first few days after adult emergence. The protein products of the mealworm testes were shown by gel electrophoresis to be many and diverse. The 27 protein products were of various molecular weights, ranging from 12,000 to 127,000 daltons. These products were present at different ages of development and persisted for various times indicating that some of these proteins may be necessary for the formation of specific germ cell types. In addition, a variety of these testicular protein components incorporated leucine at measurable levels throughout development, particularly during the pupal stage. It was ascertained that the rate of incorporation of radioactive leucine into TCA -precipitable testicular protein was not affected by the administration of exogenous juvenile hormone alone (JHI, 1 µg/animal) during the pupal stage. However, the administration of exogenous ecdysterone (0. 5 µg/animal) to pupal Tenebrio resulted in an increase in the rate of radioactive leucine incorporation into TCA -precipitable testicular proteins, particularly during the first six days after pupal ecdysis. The amount of ecdysterone injected appeared to stimulate the production of the same testicular protein components that were present during normal pupal development. Injection of a higher dose of ecdysterone (1.5 µg/animal) during some of the pupal ages appeared to alter the testicular differentiation program by enhancing the incorporation of leucine into not only the age -specific testicular protein components but also into new protein components which did not normally appear at these specific ages. Simultaneous administration of both JH and ecdysterone on mealworm pupae at specific ages indicated that there was no apparent interaction, synergistic nor antagonistic, between these two hormones. Furthermore, the incorporation rate of leucine closely resembled that rate obtained following injection of ecdysterone alone in all the pupal ages studied.
Open Access
Labeling of nonstructural carbohydrates in winter wheat stems
(Colorado State University. Libraries, 1983) Hogan, Mary Ellen, author
Fructans are polymers of fructose, which contain a terminal or subterminal glucose moiety. The biosynthetic pathway for the levan-type of fructan, found in wheat, has not been elucidated. These compounds are a significant component of the nonstructural carbohydrate fraction in winter wheat stems. They accumulate when photosynthetic production exceeds their utilization. Based on a study of the translocation of 14C-sucrose in winter wheat, Robinson (44) suggested that the fructose moiety of translocated sucrose might be used preferentially for biosynthesis of fructans. The present study tested this hypothesis. Six winter wheat plants were grown to anthesis, then labeled with 14C-glucosyl, 3H-fructosyl-sucrose for three hours. The plants were then dissected and extracted in boiling 80% ethanol for 48 hours. They were subsequently extracted with water (20°C) for 48 hours. Water extracts were hydrolyzed with 2 M trifluoroacetic acid. The hydrolyzed samples were chromatographed using one-way, descending paper chromatography. Chromatograms were cut into one cm strips and eluted with water (20°C). These eluates were analyzed using liquid scintillation spectroscopy. The same technique was used to analyze aliquots of both the original ethanol and water extracts directly. Results indicated that a greater amount of the 3H from the fructose moiety of the translocated sucrose appeared in the water extracts, than in the ethanol extracts. Ratios of 3H:14C in the water extracts were greater than those in the supplied sucrose, indicating that the fructose moiety of translocated sucrose was used preferentially in the biosynthesis of water soluble fructans. This suggests that hexoses derived from translocated sucrose were not as readily interconverted in wheat stems as in other plants. The differing 3H:14C ratios of labeled fructans along the stem may indicate the degree of tissue maturity. Older stem sections contained greater amounts of labeled fructans.
Open Access
Germination, emergence, and seed persistence of Panicum miliaceum L.
(Colorado State University. Libraries, 1984) Stump, William L. (William Loyd), author; Zimdahl, Robert L., advisor; Schweizer, E. E. (Edward E.), committee member; Stanwood, Phillip C., committee member
The effects of varying levels of temperature, moisture, and seed depth on wild proso millet (Panicum miliaceum L.) emergence were observed. The effects of depth and duration of seed burial and the effects of seed overwintering on the soil surface on modes of seed depletion and persistence were studied. Patterns of wild proso millet emergence in the field were studied under conditions of plus or minus intraspecific and corn competition, and with and without soil disturbance. Emergence occurred over a range of 10 to 40 C with percent and speed of emergence increasing with temperature. Under simulated drought conditions induced by polyethylene glycol, germination was reduced at both temperatures tested (25, 30 C) as moisture stress increased. The greatest moisture stress that germination occurred at was -14 bars (1 .5%) at 30 C and -10 bars (2%) at 25 C. Germination at 30 C was higher at all moisture levels than at 25 C. Emergence from soil moisture levels of 35 to 100% field capacity was greater than 87%. Emergence ceased below 25% field capacity. Fluctuations of soil moisture resulted in slightly higher emergence than at a constant soil moisture level. Emergence was equal from 1 to 8 cm of seed depth with 14 cm the maximum depth of emergence. After 21 months of seed burial loss was greatest at 5 cm, with only 23% viable seed remaining. Persistence increased with soil depth with 77 and 93% viable seed at 10 and 30 cm, respectively. The main mode of depletion was in situ germination which decreased with depth. Seed death was not a major factor of depletion and was not affected by depth. The majority of depletion occurred within the first 12 months with seed populations stabilizing from 12 to 21 months of burial. Seeds overwintering on the soil surface were not greatly affected with more than 96% remaining viable seed. With high soil moisture, emergence patterns were influenced by fluctuations in temperatures in late May when emergence began, to June. In July and early August when emergence ceased, soil moisture became the limiting factor. Total emergence was greatest when all competition was removed. Both intraspecific and corn competition reduced emergence in July and early August. Cultivation acted to remove competition resulting in greater total emergence than treatments with competition.
Open Access
Investigations into the nature of the potato psyllid toxin
(Colorado State University. Libraries, 1991) Abernathy, Rella L., author; Cranshaw, Whitney, advisor; Bjostad, Louis, advisor
The potato or tomato psyllid, Paratrioza cockerelli (Sulc) (Homoptera: Psyllidae) is a pest of many solanaceous crops in the western U.S. and causes a disease in potatoes and tomatoes known as "psyllid yellows". The disease is caused by a phytotoxin produced by the potato psyllid that is systemic and causes many morphological changes in the host plant which can lead to crop loss. The effects of potato psyllid feeding on the yield of several varieties of potato, tomato and pepper were investigated. Tissue cultured potatoes were studied under greenhouse conditions by infesting the plants with potato psyllids. Dramatic yield losses occurred in four cultivars of potato studied. Varietal responses showed that early maturing cultivars had less damage, as measured by loss of tuber yield, than later cultivars. Another effect caused by potato psyllid feeding was premature sprouting of newly harvested tubers. In this case, early maturing cultivars had a greater proportion of tubers sprouting than later maturing cultivars. Tomatoes and peppers were studied under field conditions and infested by naturally occurring psyllid populations. Of eight varieties of tomatoes evaluated, all sustained a loss in yield when infested with potato psyllids. A range of damage and different levels of infestation occurred within the varieties. Peppers, on the other hand did not show typical symptoms observed in tomatoes and potatoes. Of four varieties studied, only one showed a slight decrease in yield from potato psyllid infestation. Two other pepper varieties showed a gain in yield from potato psyllid feeding, though only one variety had a statistically significant increase in yield.
Open 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.
Open Access
Integrated pest management of tomato/potato psyllid, Paratrioza cockerelli (SULC) (Homoptera: Psyllidae) with emphasis on its importance in greenhouse grown tomatoes
(Colorado State University. Libraries, 1999) Al-Jabr, Ahmed Mohammad, author; Cranshaw, Whitney S., advisor; Bojstad, Louis B., committee member; Kondratieff, Boris C., committee member; Moore, Frank D., committee member
The tomato (potato) psyllid, Paratrioza cockerelli (Sulc), has developed into a key insect pest of greenhouse tomatoes of western North America and few options have been available for its management. A series of trials were thus conducted to identify techniques that could be used in establishing an integrated pest management (IPM) program for the insect. In studies investigating improvements in sampling methods for tomato psyllid, the effects of trap color, trap orientation and height in respect to the crop were evaluated. Greatest captures of adult psyllids occurred on neon-green, neon-orange and standard yellow colored traps. Traps hung near the top of tomato plants captured significantly more psyllids than traps placed near the base of plants. Traps that were shaded or not orientated to receive direct sunlight caught fewer adult psyllids than did sun-exposed traps. Screening of potential psyllid control products emphasized those that were efficacious but also compatible with other insects used in greenhouse tomato production (e.g., parasitoids for whitefly control, pollinators). Tested materials included insecticides of microbial origin (Beauveria bassiana, Verticillium lecanii, Metarhizium anisopliae), microbial-derived insecticides (spinosad), selective synthetic insecticides (acetamiprid, pymetrozine) and selective botanical products (neem) for tomato psyllid control. The capability of B. bassiana to infect tomato psyllid and produce high mortality is reported for the first time. Acetamiprid, spinosad and formulations of Beauveria bassiana were particularly effective for control of tomato psyllid, consistently providing in excess of 80 percent control. As the latter two also are reportedly compatible with beneficial insects used in greenhouse tomato production they appear to show greatest potential for use in an integrated pest management program on the crop. Also, in trials of various repellents (Azatin XL, Trilogy, SunSpray and Garlic Barrier) for deterring oviposition, SunSpray and Trilogy did result in significant reductions in oviposition on treated leaves. Two species of green lacewings, Chrysoperla carnea Stephens and C. rufilabris (Burmeister) were evaluated for potential use as biological controls of tomato psyllid. Both species were capable of completing their life cycle on tomato psyllid. Chrysoperla carnea larvae consumed approximately twice as many psyllids as did C. rufilabris, but development of the latter was 50% faster (8 days vs. 12 days). An outdoor field trial involving applications of C. carnea eggs to psyllid-infested potatoes did not produce reductions in psyllid numbers. As soil applications of imidacloprid had previously been found to be highly effective for tomato psyllid, and had registration for use on field grown tomatoes, investigations were conducted on possible non-target effects on pollinators, specifically the bumble bee Bombus terricola occidentalis (Greene). Indications of adverse effects from imidacloprid were observed during these trials, including reduced activity of bees within the hive, reduced visitation to flowers, and often, reduced survival.
Open 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.
Open 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.
Open 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.
Open 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.
Open 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.
Open Access
The mayflies (Ephemeroptera), stoneflies (Plecoptera), and caddisflies (Trichoptera) of the South Platte River Basin of Colorado, Nebraska, and Wyoming
(Colorado State University. Libraries, 2010) Heinold, Brian, author; Kondratieff, B.C. (Boris C.), advisor; Zuellig, Robert E., committee member; Cranshaw, Whitney, committee member; Loftis, Jim C., committee member
Nearly 5,000 mayfly (Ephemeroptera), stonefly (Plecoptera), and caddisfly (Trichoptera) (EPT) species records collected from the South Platte River Basin (SPRB) were compiled from literature, field surveys, and institutional and personal collections. From this effort, a total of 291 species (69 mayflies, 66 stoneflies, 156 caddisflies) representing 35 families and 134 genera are reported from 1,208 unique collection locations. The EPT fauna of the foothills transition zone appears to be the most diverse and best characterized physiographic province of the SPRB. Four caddisflies are reported from Colorado for the first time; Asynarchus circopa (Ross and Merkley), Orthotrichia cristata Morton, Leptocerus americanus Banks, and Helicopsyche n. sp. The mayflies Ephemera compar (Hagen) and Ephemerella apopsis McCafferty are apparently endemic to the South Platte River Basin; however, both species have not been reported since their original collections in 1873 and 1974, respectively. The microcaddisfly Ochrotrichia susanae Flint and Herrmann and the winter stonefly, Capnia Arapahoe Nelson and Kondratieff are currently under emergency petition in Colorado under the U.S. Endangered Species Act. Many other species were represented by few records and require further investigation to better understand their distributions.
Open Access
Evaluation of herbicides for control of Eurasian watermilfoil and sago pondweed
(Colorado State University. Libraries, 2010) Vassios, Joseph D. (Joseph Daniel), author; Nissen, Scott Jay, advisor; Ward, Sarah, committee member; Shaner, Dale L. (Dale Lester), committee member
The aquatic species Eurasian watermilfoil (Myriophyllum spicatum) and sago pondweed (Stuckenia pectinata) can act in an invasive manner, and when present can negatively impact wildlife habitat. Eurasian watermilfoil is a submersed perennial noxious weed species that is widespread across the United States. Sago pondweed is a submersed perennial species that is a native to all 50 states. Although sago pondweed is a native, it thrives and can become troublesome in irrigation canals. Experiments were conducted to evaluate herbicides to control both species. Imazamox is a newly registered aquatic herbicide that can be used to control Eurasian watermilfoil. Three laboratory experiments were conducted to examine the response of Eurasian watermilfoil to imazamox. 14C –imazamox was used to evaluate imazamox absorption rate, the influence of external imazamox concentration on absorption, imazamox desorption when plants were transferred to clean water, and imazamox absorption. Imazamox absorption by Eurasian watermilfoil was low. The weed absorbed only 0.5% of the herbicide applied 24 HAT, and reached a maximum of 0.97% 72 HAT. External concentration affected imazamox absorption, where plants absorbed 1.05 g per plant at a treatment concentration of 200 μg L-1, while at 800 μg L-1 absorption was 4.06 μg per plant. The percent of applied imazamox absorbed was the same regardless of the external concentration, indicating that absorption was the result of simple diffusion driven by a concentration gradient. Desorption after plants were placed in clean water was rapid, reaching equilibrium by 12 hours with 46% of absorbed imazamox having moved into the surrounding water. The metabolism study indicated that 144 HAT; 69.04% of absorbed 14C-imazamox was found in the bound fraction, 11.52% as soluble metabolites and 21.44% remained as imazamox. In addition to laboratory experiments, three whole lake treatments were applied and imazamox dissipation was monitored. Three greenhouse experiments on sago pondweed were conducted to evaluate herbicide control when applied pre-emergence to a soil surface simulating a dewatered irrigation canal treatment. Herbicides evaluated included imazamox, imazapyr, fluridone, penoxsulam, flumioxazin, pyroxasulfone, dimethenamid, and metolachlor. In addition to herbicide control, the effect of incorporation using simulated rainfall was evaluated. Rainfall incorporation did not have a significant effect, and all treatments resulted in a biomass reduction on 70% or greater when compared to the untreated control. In addition to greenhouse studies, four field studies were conducted. Herbicide residues were quantified in canal sediments and canal water for all sites.
Open Access
Role of Oryza sativa chitinases in disease resistance
(Colorado State University. Libraries, 2010) Snelling, Jacob Wayne, author; Leach, Jan, advisor; Lapitan, Nora Lyssa V., committee member; Chisholm, Stephen Thomas, 1972-, committee member
Plant chitinases have long been implicated in defense responses against invading pests and pathogens. In Oryza sativa cv. Nipponbare (rice), chitinases have been shown to co-localize with disease resistance QTL, and are thought to contribute to a multigenic basal defense response. Previous work has shown that overexpression of several O. sativa class I chitinases resulted in heightened resistance to the fungal pathogens Rhizoctonia solani and Magnaporthe oryzae pv. oryzae. Here, I examined the responses of several O. sativa chitinase classes to the RNAi silencing of two transcriptionally active rice chitinase genes LOC_Os02g39330 and LOC_Os04g41620. Silencing of these genes results in a reduction of expression in several additional rice chitinases, and also shows an increased susceptibility phenotype to fungal rice pathogens R. solani, M. oryzae pv. oryzae, and bacterial rice pathogen Xanthomonas oryzae pv oryzae. The relative amounts of silencing of the individual genes LOC_Os02g39330 or LOC_Os04g41620 were not significantly correlated with disease phenotype. Thus, we conclude that silencing of these target genes altered the expression of other chitinases, and perhaps other defense response genes that were not assayed, and that the combination of altered expression profiles contributed to increased susceptibility to the various pathogens.
Open 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.
Open 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.
Open Access
Examining the unpredictable nature of yellow toadflax
(Colorado State University. Libraries, 2011) Krick, Nicholas Jon, author; Beck, Kenneth George, advisor; Nissen, Scott Jay, committee member; Ward, Sarah M., committee member; Meiman, Paul J., committee member
Yellow toadflax (Linaria vulgaris Mill.) is an aggressive creeping perennial forb that was introduced to North America in the 1600's. It is now naturalized throughout the United States and Canada and is a serious weed in the Intermountain West. This plant threatens cropping systems, rangelands, and natural areas. Colorado State University Weed Science has conducted research on yellow toadflax control for more than 20 years yielding variable and inconsistent results. Short term success has been achieved; however, recommendations for acceptable long term control are unavailable. Dramatic site-to-site variation has been observed, but the source of that variation has not been determined. Yellow toadflax is an obligate outcrossing species that exhibits much genetic and phenotypic variation and may inhabit a wide range of ecosystems. The success of managing yellow toadflax might hinge on application timing; therefore, an observational study of root bud phenology was conducted for 2 years at two sites in Colorado. This study showed that yellow toadflax exhibited a pattern of root bud development and that pattern had an important relationship to flowering. Root buds were present throughout the growing season, but their numbers fluctuated. Following bud emergence in the spring, bud numbers declined until they reached their lowest counts around the full bloom/seed set growth stage. Following this growth stage, bud numbers increased suggesting the root system was a demanding carbohydrate sink. This observational study supported results from herbicide field trials. Identical herbicide efficacy trials were conducted at five separate locations in Colorado where four rates of chlorsulfuron and imazapyr were each applied in September 2008. Plants were harvested from these same sites and were subjected to a common garden experiment and an ALS enzyme bioassay. Analysis of field experiments 1 year after treatment (1 YAT) showed site variation using low herbicide rates (40 g ae ha-1 chlorsulfuron and 127 g ae ha-1 imazapyr), but most variation was overcome by increasing herbicide rates. Chlorsulfuron applied at 94 g ae ha-1 controlled more than 76% of yellow toadflax at all sites; whereas, 380 g ae ha-1 of imazapyr was necessary to overcome site to site variation, but control was ≥73% at four of five sites. Evaluations 2 YAT showed that yellow toadflax recovered at two sites. The common garden study and ALS enzyme bioassay revealed that these populations were susceptible to herbicides on a whole plant level and on a mechanistic level; confirming that herbicide resistance is not responsible for spatial variation. It appears that yellow toadflax recovery was largely driven by length of growing season and the growth stage of a population at which applications occurred. Lower elevation sites had a higher percentage of shoots flowering at the time of application and were more difficult to control. Comparing results from the field experiments to the pattern of root bud development, applications at the lower elevation sites occurred when bud numbers were decreasing or at their lowest counts. Higher elevation sites were in a more advanced growth stage, which resulted in better control likely based on the phenology of root bud development. It is likely that more buds present or developing on a plant resulted in better control because bud are strong sinks and herbicides were likely translocated to those tissues and had a greater negative effect on their root systems. Managers can utilize what has been learned though these experiments to improve their programs and management success. Management can be improved by increasing herbicide rate, but more importantly by targeting populations at their most susceptible growth stage. Although a rate increase of herbicide is necessary to overcome site variation, this should result in less overall herbicide use (decrease due to fewer tank mixes, fewer application events, and elimination of high rates of ineffective compounds), reduced costs for managers, and will decrease environmental exposure to herbicides.
Open Access
Spatial dynamics of weeds in irrigated corn
(Colorado State University. Libraries, 2011) O'Meara, Scott, author; Westra, Phil, advisor; Khosla, Rajiv, advisor; Brown, Cynthia, committee member; Reich, Robin, committee member
To view the abstract, please see the full text of the document.
Open Access
Defense response signaling for disease resistance in rice
(Colorado State University. Libraries, 2011) Bruce, Myron Anthony, author; Leach, Jan E., advisor; Chisholm, Stephen, committee member; Ranu, Rajinder, committee member; Bush, Daniel R., committee member
Plant disease resistance is often associated with a type of programmed cell death (PCD) called the hypersensitive response (HR). Upon recognition of pathogen proteins or their activity, the affected cell and surrounding cells commit to the HR to limit pathogen spread throughout the plant. This mechanism of plant disease resistance renders a pathogen avirulent on the host plant. Lesion mimics (LM) are a class of mutant or transgenic plants that spontaneously show lesions resembling the HR in the absence of biotic stress. Based on the association of the LM phenotype to cell death and its similarity to disease symptoms and the HR, this phenotype is a useful tool to dissect and understand the plant defense response. To identify genes that when mutated result in the LM phenotype in rice, we used a microarray approach. By hybridizing labeled genomic DNA from an allelic series of deletion mutants to an oligonucleotide microarray, we identified candidate genes and genic regions that were deleted in a set of mutants. For one mutant, spl1, mutations in a cytochrome P450 gene were confirmed to confer the LM phenotype. A genome browser developed to handle these microarray data is a community resource that enables researchers to rapidly identify untagged deletion mutations in rice. Members of the 14-3-3 protein family were recently shown to be positive regulators of cell death and the HR in Arabidopsis. In contrast, the work herein shows that a rice 14-3-3 protein is a negative regulator of cell death and resistance. Transgenic plants carrying a construct that silences the rice 14-3-3 gene GF14e exhibit a LM phenotype and enhanced resistance to two distinct rice pathogens, Xanthomonas oryzae pv. oryzae and Rhizoctonia solani. These GF14e-silenced plants also showed enhanced expression of genes associated with salicylic acid (SA) mediated defense responses, including members of the peroxidase gene family. The GF14e-silenced plants did not show enhanced expression of marker genes associated with the ethylene response pathway, indicating that GF14e may negatively regulate SA mediated defense responses, but does not affect ethylene regulated responses. Silencing GF14e results in the up regulation of several defense responsive peroxidases. cDNA from GF14e silenced plants was used in quantitative PCR (qPCR) to assay expression of four peroxidase genes. Of these, three showed significant upregulation in 2 weeks after sowing (WAS) and 5 WAS GF14e-silenced plants. The promoters of the three upregulated genes (PO-C1, Pox8.1, Pox22.3) contain at least one W-box element. In contrast, the peroxidase (Pox5.1) that did not show upregulation and is not upregulated in R gene mediated responses had no W-box elements. W-box elements are binding sites for the WRKY class of transcription factors. This result, coupled with bioinformatic predictions of potential rice 14-3-3 clients, and the observation that some WRKY genes are upregulated in GF14e silenced lines indicates that GF14e may negatively regulate WRKY transcription factors related to cell death and defense responses. Based on the implication that one 14-3-3 protein negatively regulates defense responses related cell death, provides a framework to develop a model for how this protein might function in the plant disease resistance response.
Open Access
Two entomological studies: 1, The potential of Methyl jasmonate applications as a pest management method on cruciferous crops. 2, Contributions to the biology of Disholcaspis quercusmamma (Walsh) (Hymenoptera: Cynipidae)
(Colorado State University. Libraries, 2011) McEwen, Crystal Lee, author; Cranshaw, Whitney, advisor; Kondratieff, B.C. (Boris C.), committee member; Stonaker, Frank H., 1958-, committee member
Methyl jasmonate (MeJA) is known for the many physiological roles in plants, including induced resistance to herbivores. Treating plants with exogenous applications of MeJA has been shown to have various effects on the behavior of herbivores. This study sought out to quantify the effects of MeJA applications on field grown cruciferous crops in both pest response and crop response. The suitability of MeJA as a pest management tool depends on the tradeoff of costs and benefits of jasmonate-induced resistance. MeJA applications were shown to reduce flea beetle (Phyllotreta spp.) feeding in a greenhouse setting. Feeding was reduced as early as the same day of treatment and feeding was further reduced over a period of 4 days. When applied in a field setting MeJA was effective at reducing the numbers of flea beetles, at least briefly, on broccoli, Chinese cabbage, Brussels sprouts, and rutabaga. MeJA applications can affect lepidopterous pests by changing oviposition preferences or by affecting development. Brussels sprouts showed a reduction in Pieris rapae (Linnaeus) and Trichoplusia ni (Hübner) eggs found on MeJA treated foliage. Conversely multiple applications of MeJA on cabbage resulted in an increase in P. rapae eggs found on foliage. Trials where larvae were reared on field grown MeJA treated food showed that P. rapae larvae developed in the same amount of time as those larvae that were reared on untreated food and that they weighed approximately the same. In that same trial, T. ni showed that male pupal periods were longer and pupae of both sexes weighed more when they were reared on MeJA treated food. MeJA applications reduced plant size in broccoli, Chinese cabbage, and Brussels sprouts. Yield was also reduced in Chinese cabbage and rutabaga. During 2009 and 2010 MeJA applications were found to have no effect on yield in broccoli. MeJA treated broccoli showed a delay in maturity during both seasons. Protein levels on MeJA treated plants were only affected in rutabaga where there was a decrease in the protein levels in the roots of plants that were treated with both MeJA and insecticides. Studies were done to clarify the biology of the cynipid gall wasp Disholcaspis quercusmamma (Walsh). This wasp was previously known only from its asexually reproducing females that develop inside conspicuous twig galls and the sexually reproducing generation has remained unidentified. Spring bud galls were identified and sexual generation adults were reared from these galls. A morphological description was developed for the sexual generation wasps and their galls. The identity of the sexual generation of D. quercusmamma was confirmed by rearing trials ad DNA analysis. The sexual generation galls were found on both of the hosts that support the asexual generation; Quercus macrocarpa Michx. and Quercus bicolor Willd. While some trees were noted to be resistant to the formation of the asexual generation gall, those same trees were found to contain the sexual generation twig galls. The sexual generation galls develop in buds and become visible in the spring after bud break. The sexual generation wasps emerge in the spring and oviposit in newly developing twigs. Parasitoids reared from the sexual generation galls that are shared with the asexual generation are Torymus denticulatus (Breland) (Torymidae) and Sycophila dubia (Walsh) (Eurytomidae). Parasitoids that appear to be unique to the sexual generation are the pteromalid species Lyrcus nr. nigroaeneus (Ashmead), and the unidentified males of Pteromalus sp. and Mesopolobus sp. New records for the parasitoids associated with the asexual generation in northern Colorado include Eurytoma querciglobuli (Fitch), T. denticulatus, and Baryscapus racemariae (Ashmead).