Theses and Dissertations

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The impact of rootstock on peach tree vigor, light environment, fruit quality, and metabolism
(Colorado State University. Libraries, 2024) Pieper, Jeffrey Ross, author; Minas, Ioannis, advisor; Bunning, Marisa, committee member; Caspari, Horst, committee member; Prenni, Jessica, committee member
The key to Colorado's successful peach industry is superb fruit quality. The fruit quality growers achieve allows for the highest premium 'farm-gate' price per pound in the nation. Fruit quality is created in the orchard via the interaction of several pre-harvest factors. One critical pre-harvest factor that has several knock-on effects for orchard management decisions is rootstock selection. Rootstock selection has the potential to impact the longevity, productivity, efficiency, and profitability of an orchard, and is dependent on climatic and edaphic environments as well as the soil microbiome. Rootstock selection may also allow growers to augment orchard design through vigor manipulation. In Colorado, growers are faced with relatively short growing seasons, sudden fall and spring frost events, and calcareous soils which limit the availability of certain nutrients. The unique growing environments coupled with the need for high quality fruit production makes rootstock selection limited. Identifying rootstocks suitable for production in Colorado and determining how they impact fruit quality is paramount. While previous studies have evaluated rootstocks for their performance and relationship to fruit quality, few have limited confounding factors such as crop load, canopy position, and or physiological maturity when assessing fruit. The following experiments evaluated twenty-one genetically diverse rootstocks for their phenotypic and agronomic performance and potential use in Colorado production systems. The nine-year performance review, in chapter one, details the productivity and suitability of seventeen genetically diverse peach rootstocks in Colorado growing conditions. The trial determined rootstock vigor strongly correlates with cumulative yield. However, vigor also showed an inverse relationship with internal fruit quality development measured as dry matter content (DMC) and soluble solids concentration (SSC). The trial showed interspecific peach and non-peach hybrids outperformed peach seedling rootstocks. One interspecific peach rootstock in particular, 'Krymsk® 86', performed exceptionally well and has since been widely adopted by industry. By controlling for several confounding factors, the rootstock vigor trial, chapter two, demonstrated the true impact of vigor and light availability on fruit quality enhancement and primary metabolite profiles. Fruit developing in reduced vigor canopy of the dwarfing rootstock 'Krymsk® 1' had increased light availability and enhanced internal fruit quality parameters (DMC and SSC) at harvest. Mesocarp metabolites relating to internal quality showed they are up and down accumulated by rootstock vigor and the light environment. Several metabolite classes including soluble sugars, cyclitols, flavanols, and chlorogenic acids were associated with 'Krymsk® 1', a low vigor rootstock that had high light availability and enhanced fruit quality profiles. 'Atlas™' and 'Bright's Hybrid® 5', both vigorous rootstocks, showed low light availability and reduced fruit quality. The vigorous rootstocks also showed an increase of amino and fatty acids compared to the standard and dwarfing rootstocks. The six-year physiological and agronomic performance of modern semi-dwarfing rootstocks trial, chapter three, reiterated the impact of vigor on yield, light availability, and fruit quality development. Furthermore, the trial showed increased vigor was related to an increase of gummosis incidence and severity. Also, intra-specific Prunus hybrids had increased rates of proleptic shoot formation, however, some showed they were susceptible to iron chlorosis. Overall, the rootstock trials identify key parameters of performance and suitability in Colorado production systems. The outcomes indicate that rootstocks with increased vigor resulted in higher yields per tree, however, lower light availability in the canopy decreased DMC and SSC. While rootstock genotype and vigor are influencing peach fruit development and quality, their effect on light availability may play a more significant role in achieving optimal yield and fruit quality and augmented metabolite profiles. Additionally, this work demonstrates the importance of controlling for confounding variables when evaluating preharvest factors for their impact on internal fruit quality and metabolite profiles.
Open Access
Bacteriomes of peaches and cover crops
(Colorado State University. Libraries, 2024) Newberger, Derek R., author; Vivanco, Jorge M., advisor; Minas, Ioannis, advisor; Paschke, Mark, committee member; Manter, Daniel, committee member
Replant syndrome (RS) of fruit and nut trees causes reduced tree vigor and crop productivity in orchard systems due to repeated plantings of closely related tree species. Although RS etiology has not been clearly defined, the causal agents are thought to be a complex of soil microorganisms combined with abiotic factors and susceptible tree genetics. Different soil disinfection techniques alleviate RS symptoms by reducing the loads of the deleterious microbiome; however, the positive effect on crop growth is temporary. Here, the current understanding of RS in orchards from a soil microbiome perspective is reviewed. The resolution to RS will require experts to outline explicit descriptions for its symptoms, determine its etiology, identify the primary phytopathogens, and fully explore sustainable treatments which alleviate RS. Two sustainable treatments of RS were selected to explore at a deeper level, soil disinfection and increasing crop diversity to observe what technique could help establish a healthy soil bacteriome. In a greenhouse study, soil disinfection via autoclave was then followed by cover cropping. It was found that soil disinfection increases plant biomass as compared to the control for only the first crop cycle while non-autoclaved soils with a history of cover cropping alleviated RS in RS-susceptible 'Lovell' peach seedlings. Although soil disinfection via autoclave was found to distinctly alter the peach soil bacteriome for the full duration of the study, this sustainable practice mimicking solarization failed to provide relief from RS for peach seedlings. Instead of long-term benefits, differential abundance comparisons displayed a loss of potentially beneficial bacteria due to soil disinfection. Paenibacillus castaneae and Bellilinea caldifistulae were beneficial bacterial species that uniquely colonized peach rhizosphere of non-autoclaved soils with a cover crop history. As a promising sustainable technique, a greater understanding of how inter-/intra-specific competition of cover crops can influence the bulk soil bacteriome was pursued. Alfalfa, brassica, and fescue were grown in 7 different plant combinations (1. alfalfa, 2. brassica, 3. fescue, 4. alfalfa-brassica, 5. alfalfa-fescue, 6. brassica-fescue, 7. alfalfa-brassica-fescue) across 3 density concentrations (low: 1–3 plants, medium: 24 plants, and high: 48 plants) for a greenhouse microcosm experiment. It was found that even in highly competitive conditions beneficial bacteria were enriched, however, there was an apparent trade-off where different plant combinations enriched distinct beneficial bacteria. As an example, even if a free-living nitrogen fixing bacteria such as an Azospirillum spp. was enriched in the bulk soil of alfalfa and brassica monocultures, it was not enriched in the bulk soil of an alfalfa-brassica plant mixture. Instead Pseudarthrobacter phenanthrenivorans, a phytohormone producer, was enriched in alfalfa-brassica plant mixtures. When zooming into the rhizosphere compartment of these microcosms, it was found that regardless of plant neighbor identity or density, a few rhizobacteria were highly correlated with a specific plant species. Meanwhile, certain plant species specific rhizobacteria were enriched only if specific conditions such as plant neighbor identity or density were met. Overall, our research found that growing diverse plant species plants prior to the re-establishment of a peach orchard could alleviate RS symptoms. Furthermore, cover crops can enrich different microbes when grown together as opposed to when grown separately. Lastly, although plants recruit a particular set of bacteria, this recruitment can shift depending on plant neighbor identity or density. Further study of cover crops may identify how they can alleviate RS in orchards worldwide.
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Drought and salinity tolerance of cool-season turfgrasses
(Colorado State University. Libraries, 2024) Li, Jizhou, author; Qian, Yaling, advisor; Burcham, Daniel C., committee member; Ham, Jay, committee member; Zhang, Yao, committee member
Due to the water scarcity and increased use of recycled water/saline water for turfgrass irrigation in arid and semi-arid climates, there is an increasing demand for drought and salt tolerant turfgrass. Kentucky bluegrass (Poa pratensis L.), tall fescue (Festuca arundinacea Schreb.), and perennial ryegrass (Lolium perenne L.) are the most commonly used cool season turfgrass species in the northern regions of the United States. The thesis includes two separate studies evaluating entries in National Turfgrass Evaluation Program (NTEP) trials. These two trials were conducted to identify the most drought tolerant lines of Kentucky bluegrass and tall fescue grown in a field study, and the most salt tolerant lines of perennial ryegrass grown in a greenhouse study, respectively. The drought tolerance trial is presented in Chapter 1. In it, the drought tolerance of thirty-five cool-season turfgrasses, including 15 Kentucky bluegrass lines, 19 tall fescue lines, and 1 perennial ryegrass line were evaluated under three deficit irrigation treatments, 40%, 60% and 80% evapotranspiration (ETo) from 2018 to 2020. Overall turfgrass quality, minimum irrigation requirement for maintaining the acceptable quality, and length of time to maintain acceptable quality were determined for each entry. The amount of irrigation needed to maintain acceptable quality for tall fescue was 71% - 95% ETo, and for Kentucky bluegrass, it was 81% - 110% ETo under three-year deficit irrigation. Based on turf quality and irrigation requirement to maintain acceptable quality during the three-year deficit irrigation period, we have identified the most drought tolerant entries. Among Kentucky bluegrass entries, "PST-K13-141" has emerged as the top performer, demonstrating an 81% ETo rate to maintain acceptable quality. Among tall fescue lines, the most drought-tolerant entries include "PST-5SDS," "Kingdom," "DLFPS 321/3679," and "Thor," requiring 71%, 74%, 74%, and 72% ETo, respectively, to uphold satisfactory turf quality. The results of this study suggest that selecting species and entries that use less water while maintaining acceptable quality could mitigate irrigation demands. In Chapter 2, the salt tolerance of eighty-three perennial ryegrass lines was evaluated in two separate greenhouse experiments. Eighty-three lines were grown in cone-shaped containers that were soaked in increasingly saline nutrient solution for 1 hour per day. The solution began with an electrical conductivity (EC) of 6.0 dS·m-1 and was subsequently increased by 4.0 dS·m-1 (in Experiment I) or 6.0 dS·m-1 (in Experiment II) every 3 weeks until reaching the next targeted salinity level. The final targeted salinity level was 22 dS·m-1. Grasses were grown under each of the 4 or 5 targeted salinity levels for a period of 3 weeks. Clipping yield reduction, overall turf quality, leaf firing, and density were determined at each salinity level. Regression analysis was conducted to determine the relationship between clipping yield and salinity. The salinity level causing a 25% reduction in clipping yield was used as an indicator of salinity tolerance level in different entries. We found that entries "SGP4", "PPG-PR 667", "PVF-SGS5", "BAR LP 22262", "GO-RUS21", "PPG-PR 610", "DLF-PR 3727", and "PPG-PR 639" were the most salt-tolerant, evidenced by the best turfgrass quality and the highest salinity levels at which there was a 25% clipping yield reduction in two experiments. We observed that the salinity levels that caused a 25% clipping yield reduction ranged from 5.0-8.8 dS·m-1 in experiment I and 5.7-10.7 dS·m-1 in experiment II. The entries with better salt tolerance identified in this study would hold the potential to be utilized on sites with marginally elevated saline soil. Additionally, they could be beneficial for locations where irrigation involves waters with elevated salinity, such as recycled water.
Open Access
Investigation of flowering phenology, pollinator and invertebrate biodiversity value on urban green roofs and an evaluation of ornamental horticulture crops for pollinator value
(Colorado State University. Libraries, 2024) Guidi, Michael A., author; Bousselot, Jennifer, advisor; Hufbauer, Ruth, committee member; Krishnan, Sarada, committee member
Urban green space, green infrastructure, and horticultural installations are gaining recognition for their potential to foster biodiversity. Green roofs are challenging growing environments for plants, characterized by extreme substrate temperatures, high light intensity, limited moisture availability, and limited substrate depth. Plants have a variety of physiological responses to these unique conditions, but little is known about how green roof growing conditions affect ecological characteristics like plant flowering phenology. Similarly, studies are only just beginning to uncover the degree to which green roofs can provision habitat and support urban biodiversity. We evaluated the flowering phenology and made in-situ pollinator observations of 15 plant taxa growing both on green roof systems and at ground level at the Denver Botanic Gardens over two growing seasons. Using the same study sites, we sampled invertebrate diversity on green roof sites and ground level using pitfall traps. Finally, using a large citizen-science dataset, we evaluated differences in pollinator visitation with a specific focus on plant nativity, cultivated origin, growth form. We found that flowering phenology is substantially earlier on green roofs compared to ground level. We also observed a greater number of pollinators on green roofs early in the season, compared to ground level, presumably due to the availability of flora resources among the observed plant taxa. We observed significantly higher substrate temperatures along with wider diurnal temperature amplitude during the growing season that may contribute to this pattern. Invertebrate abundance was substantially higher at ground-level, species richness was similar between the intensive green roof and ground-level, and we observed substantially lower abundance and richness on the extensive green roof. Divergence in flowering phenology between individual plants of the same species on green roofs and plants at ground-level may have implications for organisms that rely on floral resources in urban environments. Earlier flower initiation on green roofs may provide pollinators with unique foraging opportunities and aid targeted conservation where early-season floral resources are limited. Similarly, results from invertebrate sampling suggest that green roofs, especially intensive roofs with high vegetation coverage, species richness, and habitat heterogeneity may offer invertebrate habitat on par with ground-level urban gardens and may even support unique groups of invertebrate taxa. Our results from our citizen science pollinator observations demonstrate that non-native plants showed similar visitation compared to native plants, but origin was important with selections and species having significantly higher pollinator visitation compared to hybrid plants. Shrubs and herbaceous perennials demonstrated high pollinator visitation compared to other plant growth forms.
Open Access
Characterizing smoke taint in hops (Humulus lupulus) and investigating the impact of defoliation stress on phytocannabinoid content in industrial hemp (Cannabis sativa)
(Colorado State University. Libraries, 2024) Sandoval, Brandon, author; Prenni, Jessica, advisor; Rhodes, Davina, committee member; Broeckling, Corey, committee member
The family Cannabaceae contains at least 10 genera, with Cannabis (hemp) and Humulus (hop) being two of the most economically important. Both genera have long been valued by humans for their chemical constituents and are used today for both medicinal and recreational purposes. However, adverse environmental factors may impact the chemical profile of these important crops, leading them away from a true-to-type quality. This thesis will explore the effects of an abiotic stress on the chemical profile of each crop: smoke-taint in hops and defoliative hail damage of hemp. The Pacific Northwest contains 97.5% of U.S. commercial hop acreage and has also seen an increase in the number and severity of wildfire events in recent years. While there is extensive research from the wine industry on the impact of smoke taint in grapes, our knowledge of smoke taint in hops is limited. Here, we aimed to characterize smoke taint in hops using laboratory simulated wildfires with distinct fuel types and non-targeted gas chromatography-mass spectrometry. Our results reveal an overall variation in the chemical profiles between smoked and control hops and across fuel types and the detection of known and novel smoke taint markers including guaiacol, 4-methylguaiacol, and xylopyranose. This research provides evidence to support the use of established smoke taint markers for hop analysis and lays the groundwork for future studies to investigate various fuel types and their impact on hop quality. The United States has seen an abrupt increase in commercial industrial hemp production since the Agricultural Improvement Act of 2018. However, the historical prohibition of this crop has resulted in a lack of basic physiological research to guide management practices. For example, abiotic stress can stimulate plants to increase production of secondary metabolites such as phytocannabinoids and this is of high importance to farmers as they as they must balance optimization of CBD yield (crop value) with regulatory requirements (THC < 0.3% by mass) that could lead to crop loss (mandated destruction). In this study we evaluated the impact of defoliation stress (to simulate hail damage) at three different growth stages. Our results indicate that defoliation stress during late flowering yielded no significant change in phytocannabinoid production. However, defoliation stress during vegetative and early flowering yielded a significant increase in phytocannabinoids, including total CBD and THC, at harvest.
Open Access
A guide for small-scale organic vegetable farmers in the Rocky Mountain region
(Colorado State University. Libraries, 2009) Stonaker, Frank, author; Stushnoff, Cecil, advisor; Davis, Jessica, advisor; Cranshaw, Whitley, advisor
The steady growth over the last twenty-five years in the organic agriculture sector has been paralleled by growth in the number of farmers' markets and community-supported agriculture (CSA) operations, reflecting increased consumer interest in "buying locally". Small organic farms represent the core of the local growers involved and invested in this trend in Colorado and yet have had little research to direct or support their forays into organic agriculture. Agricultural research focusing on organic systems and the challenges in soil fertility management, pest and disease management, and plant breeding appropriate for organic production has lagged. The research in organic production that has been done in the US has occurred largely on the east and west coasts and upper Midwest where climatic conditions are different from that of the arid, inter-mountain west. In 2002 the Horticulture and Landscape Architecture Department at Colorado State University initiated the Specialty Crops Program, and soon after the Rocky Mountain Small Organic Farm Project (RMSOFP) was established to address issues relevant to small-scale organic farmers in Colorado and the region. Within this context a prototypic small organic farm was developed on certified organic land at the Horticulture Field Research Center (HFRC) neat Ft. Collins, Colorado. A variety of research projects have been undertaken ranging from cultivar trials of vegetables, to evaluations of phytochemicals of vegetables grown on organic and conventional plots. This production guide for small-scale organic farmers provides a basis for future research, education, and outreach efforts that can be made available to farmers, extension workers, teachers and students. It is a comprehensive production guide for small-scale organic farmers in the climatic zones similar to those found in Colorado. Topics included are: soil fertility management, tillage, irrigation, and pest management. Detailed production recommendations for melons, tomatoes, spinach and lettuce are presented, with cultivar trial results of melons, tomatoes and spinach. Fifteen organic vegetable farmers from Colorado were interviewed about their production practices, and their comments are included.
Open Access
Drought stress and recovery in green ash (Fraxinus pennsylvanica Marsh.)
(Colorado State University. Libraries, 2009) Litus, Gregory, author; Klett, James, advisor
Throughout the Front Range of Colorado, municipalities have developed urban forest management plans that focus on preserving the health of landscape trees and promoting an increase in the canopy cover as an offset to carbon dioxide emissions through carbon sequestration. However, drought in recent years has prompted a concerted effort to conserve water used for landscape irrigation. The combined drought and reductions in irrigation have the potentials to increase water stress in shade trees and lessen the amount of carbon sequestered. To assess the effects of drought stress on growth, photosynthesis and long term health of established green ash (Fraxinus pennsylvanica Marsh.), a record dry 2005-2006 winter was exploited so that severe drought stress could be induced. Early season drought reduced spring leaf growth by 25 percent compared to controls. As drought progressed through the growing season, the stressed trees increased intrinsic water use efficiency by controlling stomatal conductance, based on threshold water potentials, while maintaining photosynthesis. After irrigation was applied in late summer, tree water potentials, stomatal conductance and photosynthesis recovered to near pre-drought levels. The decreased photosynthesis contributed to the reduction in tree growth for the season but did not alter total non-structural carbohydrates concentrations or produce a carbohydrate deficit that would dramatically hinder growth in subsequent years. The extended drought stress followed by irrigation did not affect dormancy and cold hardiness was maintained to -50 °C. Potted green ash trees were used to determine the extent of drought stress tolerated by green ash. At a predawn leaf water potential of -5.28 MPa, stomatal conductance and photosynthesis were reduced but still measurable. Established trees exposed to severe drought conditions did not experience predawn leaf water potentials below -3.14 MPa. Considering the range of drought stress tolerated by green ash and the unlikelihood of those conditions occurring in a managed landscape, negative effects of drought stress are minimized as long as late season irrigation can be applied. However, in green ash, the timing of drought stress can permanently restrict growth in any single year and significantly reduce the total carbon sequestered through photosynthesis.
Open Access
Study of bioactive proteins in the roots and root exudates of model plants
(Colorado State University. Libraries, 2007) De-la-Peña, Clelia, author; Vivanco, Jorge M., advisor
The plant root system serves many roles, including anchorage and uptake of nutrients and water. The ability of roots to release a wide range of organic and inorganic compounds into the rhizosphere to communicate with roots of other plants and other organisms has been the focus of recent studies. Among the compounds released into the rhizosphere, proteins comprise an important amount of energy secreted by roots but have not been studied in detail. In the present study, I conducted a proteomic and enzymatic analysis of Arabidopsis thaliana root exudation across a developmental gradient to track the changes that occur in the root-secreted proteins at different plant developmental stages. Further, I found that the secretion of proteins (including pathogenesis-related [PR] proteins, myrosinases, and enzymes related to protein refolding) was qualitatively and quantitatively related to the growth stage of the plant. For instance, the intensity and activity of PR proteins such as chitinases were higher at peak flowering times than at any other time during Arabidopsis development. I also studied the root secretion of proteins by two model plants (Medicago sativa and A. thaliana) during their interaction with the symbiont of one of these specks (Sinorhizobium meliloti) and with an opportunistic pathogen of A. thaliana (Pseudomonas syringae pv. tomato DC3000). I found that the early interactions between M.sativa and S. meliloti induced exudation of enzymes such as acid chitinases, thaumatin proteins, PR10 and PR1 proteins. However, these proteins were not induced when M. saliva was inoculated with P. syringae DC3000. In addition, I found that P. syringae DC3000 could differentially induce the secretion of proteins related to defense in A. thaliana, whereas S. meliloti did not provoke the same response. The final study of my dissertation focused on the activity of ribosome-inactivating proteins (RIPS, PC 3.2.2.22) in Arabidopsis thaliana. Based on amino acid sequencing, it was determined that the purified RIP had homology to the mature form of a pectin methylesterase (PME, At1g11580); this purified protein showed PME activity. Further the A. thaliana full-length and mature PMF forms were cloned into the expression vector PQE30 and both constructs were expressed in Escherichia coli.
Open Access
Heritability estimates, accession evaluation, and digital imaging in Distichlis spicata
(Colorado State University. Libraries, 2009) Christensen, Dana K., author; Koski, Anthony, advisor; Holm, David, advisor
Conserving water in the landscape is critical to inhabiting the arid portions of the western United States. Native accessions of the inland form of saltgrass [Distichlis spicata var stricta (Torr.) Beetle] remained green, while turfgrass lines of blue grama, buffalograss, crested wheatgrass, and bermudagrass went dormant from lack of rainfall during the drought of 2000 and 2001 in Colorado. Since saltgrass is non-domesticated, this research selected plants for four traits needing improvement to make saltgrass more turf like. Resistance to leaf rust (Puccinia aristidae Tracy), short height, high shoot density, and high seed yield were traits that made up a selection index which ranked all 158 accessions collected from the Front Range of Colorado, the Great Basin, South Dakota, and Nebraska. The top 14 females and 12 males of these were topcrossed, and progenies were evaluated. Response to selection was recorded for all four traits. Realized heritability, narrow sense heritability from half-sib analysis, narrow sense heritability from parent-offspring regression, and broad sense heritability were very high for height and shoot density. Broad sense heritability and narrow sense heritability from half-sib analysis were high for seed yield, but narrow sense heritability from parent-offspring regression and realized heritability were moderate. A major gene for rust resistance was inferred. Negative heterosis measured on the midparent for height and seed yield were noted. Positive heterosis occurred for shoot density.
Open Access
Development and utilization of molecular tools to understand invasion biology in Centaurea maculosa (spotted knapweed)
(Colorado State University. Libraries, 2009) Broz, Amanda K., author; Vivanco, Jorge, advisor
My doctoral research at Colorado State University was designed to create and utilize molecular tools to help understand ecological phenomena in the invasive weed, spotted knapweed (Centaurea maculosa Lam.). In this dissertation, I first introduce the need for research at multiple scales and the potential benefits of collectively examining molecular, physiological and ecological phenomena in an invasive plant. I then give a brief overview of the life history characteristics of spotted knapweed and report on the development and characterization of a spotted knapweed gene library. By utilizing sequence information from the gene library, I determined that both ploidy (diploid or tetraploid) and origin (native or invasive) influence expression of genes that may be important for plant defense in spotted knapweed populations. I found that spotted knapweed can differentially respond to strong or weak competitors at the level of gene expression by using existing molecular tools from a model plant coupled with sequence information from the gene library. In addition, I found that plant neighbor identity, simulated herbivory and resource availability are all important factors that influence accumulation of biomass and secondary metabolites in both spotted knapweed and a native grass species. I utilized molecular tools to demonstrate that spotted knapweed infestation alters the composition of North American soil fungal communities; however, the ecological ramifications of this observation remain undetermined. The major goal of my research was to better understand spotted knapweed invasion biology by utilizing molecular tools. I believe this approach was successful in that it led to a variety of interesting results. However, more research is required to fully link these molecular findings with ecological and physiological aspects of spotted knapweed invasion biology. It is my hope that the chapters of this dissertation highlight both the opportunities and limitations associated with using molecular tools to understand invasion biology in this system.
Open Access
Relative total phenolics in potato (Solanum tuberosum L.) progeny from 15 families
(Colorado State University. Libraries, 2009) Al-Daej, Mohammed Ibrahim, author; Hughes, Harrison G., advisor
Potatoes are the fourth most important food crop by consumption in the world. Since antioxidants have been identified as having health benefits related to reducing free radicals, there is interest in increasing the levels of antioxidants in new potato cultivars. The objectives of this study were to: (1) Determine the total phenolics content (TPC) of progenies of 15 families derived from crosses of clones grown in the San Luis Valley (SLV), Colorado (CO). (2) Determine if pigment level as measured by MiniScan® XE Plus could be used as a method to identify high TPC tubers. (3) Study the correlation between TPC of all tubers and families' means harvested from the field with corresponding families' means and tubers harvested from the greenhouse (GH).
Open Access
Antioxidant properties of date palm (Phoenix dactylifera L.) cultivars
(Colorado State University. Libraries, 2008) Al-Turki, Saleh Mobarak, author; Stushnoff, Cecil, advisor
The fruit and pits of date palm (Phoenix dactylifera L.) cultivars from the United States (US) and Saudi Arabia (SA) were analyzed for their total phenolic contents and antioxidant activity for two years. The amount of total phenolic compounds and antioxidant activity in all date fruit and pit cultivars tested in this study, at the Tamar stage, were significantly different. Total phenolic contents of fruit ranged from 507.03 (Gur SA) to 225.02 (Medjool US) mg Gallic Acid Equivalents (GAE)/100g FW and antioxidant activities ranged from 1400.14 to 228.06 μmole TEAC/100g of fresh weight (ABTS) in Deglet Noor US and Khalasa US respectively. DPPH of fruit ranged from 117.75 to 165.42 μmole TEAC/100g of fresh weight in Deglet Noor (US) and Khalasa (US) respectively. The pit, which is about 12% of date fruit weight, ranged from 66.68 (Hilali US) to 14.51 (Amir Hajj US) mg GAE/g DW total phenolics. ABTS ranged from 679.01 to 45.83 µmole TEAC/1g of dry weight in Hilali US and Hayany (US) respectively. DPPH ranged from 15.94 to 3.92 μmole TEAC/g of dry weight in Sukari (SA) and Khalasa (SA) respectively. A significant association between the total phenolic content and antioxidant activities was found in both years with ABTS and DPPH. Moreover, there was a strong relationship between measurement of antioxidant capacity by ABTS and DPPH in both years in fruit and pits. Fruit of one cultivar, Khalasa, was available both years from the (US) and (SA). Phenolic content, ABTS and DPPH radical scavenging capacity of fruit and pits differed in their antioxidant activity due to different location and other environmental factors. Fruit or pit (SA) cultivar was significantly higher than the (US) cultivar over all treatments. Deglet Noor (US) fruit which makes up about 90% of California's date crop was found to be the best over all cultivars of those tested in this study. Hilali (US) was the best antioxidant source of date pit cultivars in (US), whereas, Sukari (SA) was the best antioxidant source of pits in (SA). Thus, this research demonstrates the potential of date fruit and pits as antioxidant functional food ingredients.
Embargo
The influence of genotype, environment, and storage time on the ascorbic acid content and retention in potato germplasm from the Colorado Potato Breeding and Selection Program
(Colorado State University. Libraries, 2023) Tikhonova, Olga, author; Holm, David G., advisor; Jayanty, Sastry, advisor; Heuberger, Adam, committee member; Weir, Tiffany, committee member
Potato is a globally consumed vegetable crop known to contain vitamin C, with its active form, ascorbic acid (AsA), serving as a potent antioxidant involved in numerous physiological processes within the human body. The oxidized form, dehydroascorbic acid (DHA) was not measured in this study. Thus, the focus of this thesis was to investigate ascorbic acid in potato germplasm in the Colorado Potato Breeding and Selection Program. However, even if a potato genotype contains a sufficiently large amount of AsA, immediately after harvesting, its content may significantly decrease during storage. Therefore, it is so important to focus not only on the initial AsA content but also on its retention in storage. An investigation was conducted to enhance our understanding of the potential to increase AsA content in potato tubers through traditional breeding. This study examined the variations in AsA levels due to genetic factors (assaying multiple genotypes), environmental conditions (different growing locations), and AsA retention (sampling during storage). This study was divided into 2 parts. In Part 1 (Year 1, 2021), AsA initial level and its retention during storage was investigated in 34 genotypes grown in the San Luis Valley, CO, USA. The initial AsA content ranged from 8.5 to 37.7 mg/100 g FW. All genotypes experienced some level of AsA loss during storage, with the mean loss across all 34 genotypes being 34.8%. Notably, there was considerable variation in both initial AsA levels and retention among the genotypes, with some even exhibiting a temporary increase in AsA content during storage. In Part 2 (Year 2, 2022), six cultivars (selected from 34 from last year) were grown in three different locations to investigate the effect of environmental conditions on the initial content of AsA and retention. Among the genotypes examined, three showed evidence of variation between AsA retention and growing location (time:environment, TxE interaction), indicated by varying slopes. Four genotypes demonstrated variation in initial AsA content over three different locations, representing a genotype:environment, (GxE) interaction. In conclusion, this investigation emphasizes the potential for improving potato tuber AsA content through traditional breeding, while also underscoring the significance of considering both the initial content and retention during storage to maximize nutritional benefits. This research highlights the complex interactions between genetics (genotype), environment (growing location), and storage time that influence AsA retention in this widely consumed vegetable.
Open Access
Investigation of substrate selection and finishing protocols for nursery container production of 13 plant taxa native to the southwestern United States
(Colorado State University. Libraries, 2023) Linfield, Allisa, author; Bousselot, Jennifer, advisor; Gu, Mengmeng, committee member; Davis, Jessica, committee member; Shonle, Irene, committee member
Nursery-produced native plant taxa are a tool for habitat restoration, and their use extends beyond wildlife areas as urban residents seek to create wildlife corridors. Water conservation concerns and understanding of pollinator decline further motivates use of native plants in cultivated and designed landscapes. Furthermore, increasing awareness around degradation of peatlands, drives consumer interest in sustainably produced plant material using peat-alternative substrates. Growers attempt to meet the demand for native plant material, but protocols for growing these taxa, which are not adapted to thrive in peat-based substrates, are limited. Without finishing protocols for sizing up propagules to retail size, growers, who are limited by time and resources, amend peat-based substrates using trial and error in hopes of achieving favorable growing outcomes. We identified grower practices through a survey of nationwide Plant Select® growers. Based on survey results, we evaluated survivability and plant growth in response to partially replacing peat-based substrate with sand, field soil, a microbial-inoculated compost (MIC), and a green waste compost (GWC). Our results indicated that plant growth response to these substrates is taxon specific. However, only one of the 13 taxa evaluated resulted in a significantly higher plant growth index (PGI) increase in the control group. Thus, our findings suggest that 12 of the investigated taxa may respond to peat-reduced substrates during the finishing period without significant negative impacts on PGI or dry weight.
Open Access
Addressing the threat of frost damage on peach floral buds through large-scale cold hardiness phenotyping, dynamic weather modeling and non-targeted metabolomic and proteomic analysis
(Colorado State University. Libraries, 2023) Sterle, David, author; Minas, Ioannis, advisor; Sharp, Julia, committee member; Prenni, Jessica, committee member; Caspari, Horst, committee member
Cold damage to reproductive tissues is the greatest threat to the profitability of peach (Prunus persica) growers worldwide. Cold hardiness is the extent to which peach floral buds super-freeze without suffering lethal damage. Although no changes are visible externally to floral buds for much of the dormant season, cold hardiness fluctuates as they acclimate, deacclimate and respond to abiotic stressors such as temperature or drought. A greater understanding of the mechanisms involved in these fluctuations involves accurate and frequent measurement of the extent to which cold hardiness is changing, and the ambient weather factors influencing the changes, at different stages of the dormant season. Warmer or more erratic temperature changes during the dormant season threatens peach floral buds to more frequently receive frost damage if cold hardiness becomes misaligned with the timing of lethally cold weather events. Statistical analysis of the trends and forces impacting the cold hardiness of floral buds can help identify significant patterns. These patterns can be used to better understand the physiological mechanisms affecting cold hardiness changes, and they can be used to help predict the impact of weather conditions on cold hardiness. In addition to their use in a practical sense by growers to aid in frost management decisions, accurate cold hardiness prediction models can be used to estimate what effects foreseeable climate effects can have on the outlook of future peach production. Metabolic changes are known to occur in dormant plants, although the effects of the metabolome in peaches on cold hardiness are unknown. Changes associated with cold hardiness likely follow several trends. One such trend is the fluctuations of metabolic abundances across the season, which are more associated with the endodormancy, and ecodormancy phases and the prebloom phase. These trends likely take place every dormant season as buds undergo a steady process of acclimating and deacclimating. Another trend is the response floral buds exhibit in response to acute cold events, in order to rapidly increase cold hardiness. The study of this response necessitates the monitoring of cold hardiness as well as the metabolic shift to the weather event. The response can be further elucidated by comparing cold hardiness and metabolic changes between genotypes that have different cold hardiness phenotypes. By exploring changes a cold hardy genotype undergoes, geneticists may be able to target certain metabolic expressions that may increase the frost tolerance of future cultivars. Since frost damage can be so destructive to peach production, it is necessary to understand the risks to the peach industry moving forward surrounding climate change, and it is also necessary to understand the extent to which frost tolerance can be improved in future cultivars. This study uses a multifaceted approach to cold hardiness which involves improved and large-scale cold hardiness phenotyping using differential thermal analysis, dynamic weather prediction models and associated metabolic regulation understanding.
Open Access
Bridging the gap between biofortification and consumption: evaluating sorghum grain carotenoid degradation
(Colorado State University. Libraries, 2023) Lepard, Ariel, author; Rhodes, Davina, advisor; Van Buiten, Charlene, committee member; Prenni, Jessica, committee member; Scanlin, Laurie, committee member
Sorghum (Sorghum bicolor) is a major staple cereal crop consumed in sub-Saharan Africa and Southeast Asia, where some of the highest rates of vitamin A deficiency (VAD) are found. As with most cereals, sorghum has low concentrations of provitamin A carotenoids, which are converted to vitamin A in the body. Biofortification provides an opportunity to address VAD through the nutritional improvement of sorghum grain using a non-transgenic breeding approach to increase grain carotenoids. Though vitamin A biofortification in sorghum is possible, it is unknown if breeding for high carotenoids in the grain negatively affects carotenoid pathway functions in other tissues. Additionally, it is unknown if degradation during postharvest processing occurs to a significant degree in biofortified grain. To establish how breeding for high carotenoids in the grain affects the carotenoid pathway in other plant tissues, expression of ten genes in the carotenoid precursor, biosynthesis, or degradation pathways were evaluated in the grain, leaf, and root tissues. A correlation in the gene expression within the plant tissue, but not between the plant tissues, was found for most genes, which suggests that several of the carotenoid precursor, biosynthesis, and degradation genes are controlled by tissue-specific regulation. Correlation of carotenoid concentrations and gene expression was also found to be tissue specific, which further suggests tissue-specific regulation. The selection of genes with tissue-specific regulation for marker-assisted breeding reduces the chances of grain biofortification negatively affecting other tissues. Once carotenoids have been increased in the grain, it must be noted that vitamin A is not stable in most storage, processing, and cooking environments due to oxidative stress from light, heat, and oxygen. The degradation of the nutritional quality through post-harvest processing was evaluated by sampling carotenoid grain throughout harvest, drying, storage, processing, and cooking. Individual processing steps did not cause significant degradation but added up to significant degradation by the final cooking step, with ~39% of β-carotene loss. No significant difference between the loss in the different storage temperatures or cooking styles was seen. An increase in the target value from 4 μg β-carotene/g of sorghum to 5.6 μg/g will be needed to account for processing loss in order to provide 50% of the estimated average requirement (EAR) of vitamin A. Overall, both the information on tissue specific gene expression, and post-harvest degradation will further advance the development of carotenoid biofortified sorghum lines.
Open Access
Impact of various factors on partial least squares model robustness for nondestructive peach fruit quality assessment
(Colorado State University. Libraries, 2023) Pott, Jakob, author; Minas, Ioannis, advisor; Eakes, Joe, committee member; Koslovsky, Matt, committee member
Given declining fruit consumption due to poor fruit quality and large amounts of waste, peach growers have continuously suffered from financial loss and the industry has seen a sharp decline in recent decades. Due to the time consuming and destructive nature of conventional fruit quality assessment, many peach growers prioritize fruit characteristics conducive to shipping and storage over characteristics which correlate with consumer acceptance. This prioritization has resulted in the poor-quality fruit which consumers have grown to associate with fresh peaches and contributed to large annual waste. A potential solution is the use of near-infrared spectroscopy (Vis-NIRS) paired with partial least squares (PLS) modeling, as a field deployable method that can be used to measure preharvest internal fruit quality to produce information quickly and non-destructively. These qualities offer an answer to declining fruit quality and waste. Although promising, the technology is only as good as the data used to train the models. Quality data is hard to collect as it requires the consideration of many factors including the temperature of the sample and the inclusion of biological variability impacted by seasonal changes, cultivar differences, fruit maturity, and many management factors such as crop load, rootstocks, irrigation regimes, and training systems to capture the relationships needed for good model performance. In tree fruit research, handheld Vis-NIRS devices have been used to predict internal quality parameters such as sweetness (dry matter content, DMC; soluble solids concentration, SSC) and fruit physiological maturity related to chlorophyll content (index of absorbance difference, IAD). Although accurate, the statistical models used to make such predictions often struggle with robustness across cultivars and growing seasons and regions due to a lack of biological variability, or a lack of representative data from factors like temperature. These challenges have led to slow industry adoption. To address this issue, models for 13 distinct peach cultivars were constructed by combining data from two seasons (2016 and 2021) followed by external validation with data from a third season (2022). The data from 2016 was collected over a range of preharvest factors, fruit development stages and temperatures, and the inclusion of 2021 data added additional biological variability. External validation produced error rates of 0.36 - 0.42%, 0.59 - 0.63%, and 0.05 - 0.04 for DMC, SSC and IAD, respectively, across the 13 peach cultivars indicating the models trained in 2021 were robust and performing at an acceptable level to impact grower decision making. It was observed that the additional inclusion of data from different cultivars and growing environments, as well as a third growing season (2017) did not significantly impact model performance. The lack of improvement suggests that the data from each year contain enough covariate variability to cover a broad range of measurements (i.e. input values) that growers and researchers are likely to observe when collecting data to predict peach quality in different orchards or seasons. This insensitivity to various environmental and growing conditions, generally referred to as external factors, due to the variability captured in the data used to build model is characteristic of a robust model.
Open Access
Plant growth under photovoltaic arrays of varying transparencies – a study of plant response to light and shadow in agrivoltaic systems
(Colorado State University. Libraries, 2023) Hickey, Thomas, author; Bousselot, Jennifer, advisor; Uchanski, Mark, advisor; Harrow, Del, committee member
Amidst the rising global pressures put on the interdependent systems in the food, energy, and water nexus, this document highlights the potential for systems-based solutions at the intersection of food cultivation, ecosystem services, and energy production in urban and rural environments. Agrivoltaics (APV) is a land-use model that enables simultaneous cultivation of food crops and electricity generation on the same plot of land. Agrivoltaic systems integrate solar photovoltaic (PV) energy generation with agricultural operations, maximizing the utilization of solar energy. This approach has gained significant research interest in the United States with scalable implementation is on the horizon. Research efforts at Colorado State University (CSU) aim to advance the understanding of plant responses to various shade conditions under PV arrays, benefiting stakeholders in agriculture, solar energy industries, policymakers, and governmental agencies. In particular, agrivoltaic research conducted at CSU's Horticulture and Landscape Architecture (HLA) department has focused on open field specialty crops and native pollinator plant species while documenting the overarching light and temperature growing environment. A replicated 2-year crop trial was conducted at the open field test site, comparing crop yield and growing conditions under three different PV module types with varying transparencies to traditional full sun production. Statistical analysis revealed a reduction in squash yield directly under the PV panels while no significant differences in yield for bell peppers, jalapeno peppers, lettuce and tomatoes growing north and south of the arrays. In a separate study, a simulated green roof structure was constructed around an existing PV array at CSU's Foothills Campus to explore the feasibility of rooftop agrivoltaics. A one-year study of six native pollinator plant species was conducted to assess differences in establishment, survivability, growth index, and growing conditions between full sun and PV shade environments. Overall, there were no statistically significant differences in mean Plant Growth Index (PGI) throughout the establishment season, however, notable variations in overwinter survivability were observed. In both studies the PV modules moderated the environment, resulting in lower maximum daytime ambient temperatures and even greater reduction in soil temperature throughout the growing season. Light levels are reduced under all PV module types with the least reduction under semi-transparent modules. Variations in growing conditions in these APV systems indicate the need for further research to optimize PV systems in order to maximize energy production and plant vitality.
Open Access
Quantitative analysis of runoff in green roof structures in the Colorado Front Range
(Colorado State University. Libraries, 2023) Salerno, Amanda, author; Bousselot, Jennifer, advisor; Choi, Jane, committee member; Sharvelle, Sybil, committee member
The green roof capacity of retaining rainwater extends the runoff duration further than the actual rain event, releasing part of it slowly into the drainage system and positively impacting it. However, the volumes will depend on the size of the rainfall event and the green roof design. Therefore, specific attention should be paid when designing a new green roof project, like geographic locations, materials peculiarities, and the project's needs, including biotic and abiotic design components. The need for more local data regarding this analysis in Western North America is still significant. Therefore, this study aims to analyze the impact of three different green roof systems on Colorado's climate by reduction of runoff, retention volume, and runoff coefficient. Moreover, we aim to analyze plant health and substrate moisture retention and components for better water capture. To achieve the goals outlined, three different green roofs technologies, with different retention and detention layers technologies, and a control roof, a conventional low slope roof for comparison, are placed at Colorado State University in Fort Collins, Colorado, United States; the systems include a Sempergreen Purple Roof, a Sempergreen Sponge Roof, and a Green Roof Technology with an Extenduct Drainage System; all were vegetated with Sedum mats, base slopes of 1% toward the rooftop drain, and measuring 1m x 2m. The drainage systems in each green roof were designed to test performance under steady, low-intensity, high-intensity, short-duration, and long-duration rainfall conditions and simulated rain events. All the systems have the same drain system connected to a v-notch weir. Volume, speed, and time were measured to quantify the runoff from all roof systems. Our data suggests that green roof volume capture varies with preexisting substrate moisture conditions, frequency and size of storms, and drainage layer components. Green Roof Technology with an Extenduct Drainage System and Sponge Roof had the best volume retention in less intense, more frequent, and back-to-back rainfall events. On the other hand, Purple Roof performed better for larger rain events that might lead to flooding and urban drainage concerns in cities. Ultimately, the Colorado-specific data from this study will enable the intentional design of green roofs to optimize plant health and water management.
Open Access
Nitrogen fertilizer impacts on soil microbiome and tomato plant development
(Colorado State University. Libraries, 2023) Rohrbaugh, Carley, author; Vivanco, Jorge, advisor; Delgado, Jorge, committee member; Fonte, Steven, committee member; Manter, Daniel, committee member
Nitrogen (N) fertilization largely supports agricultural production. Urea is a common N amendment used in agriculture and when overapplied it has negative consequences in the environment due to its highly labile and reactive form. Alternative fertilizers, such as controlled release fertilizers (CRF) have been designed to diminish the harmful effects of applied N. This thesis investigates and makes comparisons regarding N fertilizer types and their effects on microbial community composition and plant development. Both research questions were addressed by growing tomato (Solanum lycopersicum 'Rutgers') plants as the test crop, which serve as a good model crop for indoor greenhouse production and were grown to the vegetative stage in both studies covered in this thesis. The fertilizer types considered are urea, a quick releasing form of N fertilizer and Environmentally Smart Nitrogen (ESN), a controlled release fertilizer. The soil used in these studies was from a low N plot (5.2 mg/L NO3) from the Agricultural Research, Development and Education Center (ARDEC) in Fort Collins, Colorado. The first research question addressed in Chapter 2 examines how different types of N fertilizers compare under different soil conditions and fertilizer rates. Altering the soil microbiome through sterilization (via autoclave processing) allows us to understand how urea and a controlled release fertilizer compare in their impact on microbial community composition and N assimilation by a tomato crop. It was found in this study that the use of ESN promoted plant performance and enhanced soil nitrate concentration. The soil microbiome findings from this first experiment showed that high rates of nitrogen fertilization led to higher relative abundances of nitrifying bacteria species. The second research question addressed in Chapter 3 follows a developmental study to track how N fertilizer impacts tomato plant performance, rhizosphere microbiome assembly, and plant nutrient uptake by sampling weekly for eight weeks. It was found in this study that ESN enhanced nitrogen use efficiency and plant nitrogen uptake. The soil microbiome results indicated a shift in community structure at the middle stage of the rhizosphere development. By studying the plant growth and rhizosphere microbiome response to urea and a controlled release fertilizer applied soil, we can improve our understanding on N release rates and bacteria that are responsive to these agents. This is the first research to our knowledge examining N fertilization's impact on rhizosphere development during early to vegetative growth using, especially using a weekly sampling resolution.