Theses and Dissertations

Permanent URI for this collectionhttps://hdl.handle.net/10217/100454

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Understanding toxic elements in agricultural products: integrating insights from ionomics and arsenic speciation
(Colorado State University. Libraries, 2024) Jones, Rachel Rose, author; Prenni, Jessica, advisor; Chitwood-Brown, Jessica, committee member; Davis, Jessica, committee member; Rhodes, Davina, committee member
We humans are very unlikely to move through the world without encountering toxic elements. Throughout our history, we have viewed toxic elements through a variety of lenses: as medicines, poisons, plumbing material, pesticides, environmental threats. They are present in air, soil, water, and – as a result – food. Their geographic distribution is influenced by both natural geologic processes and our own actions, and the burden of exposure does not necessarily fall equitably across communities. Different toxic elements have different physiological effects, threshold concentrations of concern, and distributions in the food supply. Even a single toxic element can take on various chemical forms with varying toxicities. These elements continue to cause human suffering as they make their way into our diets, and we continue to learn about them. However, the large degree of chemical variation associated not only with toxic elements themselves, but also the food matrices they exist within, demand ongoing development of robust analytical methods. This dissertation assesses current availability and operationalization of data on toxic metals in the food supply and discusses a study of many different elements – including multiple toxic elements – in diverse foods. This study illustrates the importance of both understanding the large variation in toxic metal concentrations that can exist between different foods, and the co- occurrence of toxic and nutritive elements in foods. The second half of the dissertation focuses more specifically on arsenic, which is acutely toxic in some chemical forms, much less worrying in others, and of uncertain concern in others still. Understanding the distribution of these chemical forms in a high-arsenic matrix is critical for understanding the potential risk posed by the product. Analytical techniques capable of providing this data are known as speciation methods. After describing development of an arsenic speciation method in hemp, the dissertation concludes with a study applying the method to a panel of foods that may be high in total arsenic.
Open Access
Characterizing the link between cytoplasmic male sterility and PVY resistance in potato
(Colorado State University. Libraries, 2024) Yilmaz, Esra, author; Chitwood-Brown, Jessica, advisor; Rhodes, Davina, committee member; Nachappa, Punya, committee member; Chikh-Ali, Mohamad, committee member
Cytoplasmic male sterility (CMS) in potatoes is a common reproductive issue in Potato Virus Y (PVY) breeding programs, as resistant sources typically have a wild cytoplasmic background (W, D, or T). In the San Luis Valley breeding program, the cytoplasmic types and PVY resistant clones' density are unknown. Similarly, the effects of these cytoplasmic types and resistance genes on reproductive traits have not been determined. This study aimed to characterize the cytoplasm types and investigate cytoplasm types and resistance genes' effects on pollen viability, pollen quantity, and seed set. The presence of T and W cytoplasm types was determined among the seven clones, with W type being more prevalent. This finding indicates that PVY resistant genes are concentrated between only these two cytoplasmic types. While the analysis revealed an impact of the cytoplasm types and genes on pollen viability, no significant differences were found in pollen quantity or seed set. All clones exhibited absent or low pollen viability and produced either absent or minimal amounts of pollen, suggesting low male fertility levels. The observed differences in pollen viability and seed set are thought to stem from difficulties in crossing and the influence of the female clones used. Notably, no berries were obtained from clones carrying the Rysto gene with W type cytoplasm, indicating their complete male sterility. The characterization of these cytoplasm types and the male sterility status will influence breeders in designing efficient mating combinations and will contribute to sustainable seed production, which requires a substantial quantity of seeds per cross.
Open Access
Dynamic manipulation of far-red light and temperature for the production of microgreens in controlled environments
(Colorado State University. Libraries, 2024) Fulton, Oliver Wynne, author; Craver, Joshua, advisor; Bousselot, Jennifer, committee member; Johnson, Sarah, committee member
Microgreens are becoming increasingly popular for controlled environments due to their ease of production, profitability, and high concentration of nutrients. However, to date there is little information on how light spectra and temperature interactively affect plant growth and morphology to optimize the production of horticultural crops, including microgreens. Therefore, the objective of this study was to investigate the benefit of reducing air temperature as well as supplementing with far-red (700-750 nm) photons to enhance the morphology and phytochemical concentrations of three Brassica microgreen species. Seeds of mustard (Brassica juncea 'Garnet Giant'), kohlrabi (Brassica oleracea var. gongylodes), and red cabbage (Brassica oleracea var. capitata) were sown on rockwool substrate and grown in walk-in growth chambers using ebb and flow hydroponic systems at the CSU Spur campus. Upon germination, microgreens were grown under ambient air temperature of either 18 or 21 °C and subjected to the following lighting treatments: photosynthetic photon flux density (PPFD) of 165 μmol·m−2·s−1 (PAR165); PPFD of 200 μmol·m−2·s−1 (PAR200); and PPFD of 165 μmol·m−2·s−1 + 35 μmol·m−2·s−1 of far-red light (PAR165+FR35). Expected shade avoidance responses (e.g., increased hypocotyl elongation) due to a low R:FR value occurred in all three species under PAR165+FR35, regardless of temperature. Additionally, fresh weight of red cabbage and kohlrabi was greatest under PAR165+FR35 or similar between PAR165+FR35 and PAR200, respectively, at both temperatures. While an interaction with temperature was not observed, results support the role of far-red light in the manipulation of both microgreen quality and biomass accumulation. A follow-up experiment was conducted with red cabbage microgreens grown under the previous far-red lighting treatment (PAR165+FR35) to explore the dynamic manipulation of air temperature throughout production. While production under PAR165+FR35 should result in characteristic shade avoidance responses, including a potential decrease in pigmentation, we hypothesized that a reduction in air temperature during production could serve as a secondary stressor to increase phytochemical concentrations (e.g., anthocyanins). Using the same experimental setup described for the previous experiment, red cabbage microgreens were grown at an air temperature of 21 °C for 12 days (Control) or moved 6, 8, 10, or 11 days after sowing to an air temperature of 16 °C. Shade avoidance responses (e.g., hypocotyl elongation) and both fresh and dry weight were reduced for microgreens transferred to the air temperature of 16 °C on days 6 and 10 compared to all other treatments. Interestingly, microgreens transferred to the air temperature of 16 °C resulted in greater dry weight compared to Control. While results were not significant, an anticipated trend of increased relative anthocyanin content in response to longer durations at the 16 °C air temperature was observed. Although the dynamic manipulation of both far-red light and temperature could lead to microgreens with optimal yield, morphological characteristics, and phytochemical concentrations, future research is warranted to elucidate target environmental setpoints, durations, and possible interactions.
Open Access
Development of a high-throughput phenotyping method for measuring sorghum carotenoids
(Colorado State University. Libraries, 2024) Zapata Carvajal, Nelson David, author; Rhodes, Davina, advisor; Prenni, Jessica, committee member; Weir, Tiffany, committee member
Vitamin A deficiency is the leading cause of preventable blindness in young children, and also leads to infertility and decreased immune function. Humans cannot synthesize vitamin A, so it must be consumed in the diet, either as preformed vitamin A or as provitamin carotenoid (PVACs) in plant foods. Access to PVACs is limited in sub-Saharan Africa where many diets are less diverse and primarily consist of cereals, such as sorghum, with intrinsically low concentrations of PVACs. Therefore, biofortification breeding efforts aim to increase PVACs to biologically relevant levels to reduce global vitamin A deficiency. In order to select and breed high carotenoid varieties, thousands of progeny in a breeding program must be phenotyped. High-performance liquid chromatography (HPLC) is the gold standard carotenoid phenotyping method; however, it is expensive and time-consuming, making it impractical for large-scale screening. We hypothesized that a high-throughput phenotyping (HTP) method using UV-VIS spectrophotometry can identify high carotenoid sorghum lines for selection during breeding. In this study, a simple and rapid method for carotenoid extraction and UV-VIS spectrophotometric detection in a 96-well plate format was developed and validated. To develop the HTP method, we measured 60 samples using both HPLC and UV-VIS, identifying a strong correlation (R2=0.62, p-value<4.51x10-14) between total carotenoid concentrations measured with the HTP method and the gold standard HPLC method. To validate the HTP method, we measured carotenoids in 249 lines in a biparental breeding family, using both HPLC and UV-VIS, and again identified a strong correlation (R2=0.61, p-value<2.2x10-16). We also compared the predictability of the UV-VIS method to that of a simple visual inspection of grain color and found that the UV-VIS method performed significantly better. This promising HTP method will enable rapid screening of a large number of samples, helping breeders more efficiently make selections for carotenoid biofortification.
Embargo
Efficacy and impact of sanitizers in controlling pathogenic bacteria on irrigation water
(Colorado State University. Libraries, 2024) Santillan Oleas, Valeria Paola, author; Gutierrez-Rodriguez, Eduardo, advisor; Geornaras, Gina, committee member; Uchanski, Mark, committee member; Ma, Jianbing, committee member
Irrigation water quality is crucial for fresh produce. However, the absence of practical microbial water standards and EPA-registered sanitizers poses challenges for growers, impacting food security and increasing the risk of foodborne outbreaks. This study compared the effectiveness of commercial sanitizers (sodium hypochlorite - Chlo, peroxyacetic acid - PAA) and novel chemistries (sodium acid sulfate - SAS, potassium acid sulfate - KAS) at different concentrations for achieving a 3-log reduction of E. coli O157:H7 (EHEC), Salmonella (SM), or Listeria monocytogenes (LM). Additionally, the study examined their corrosive effects on aluminum and stainless steel, as well as their impact on plant and soil chemical and physical properties. Sanitizer evaluations were conducted under varying turbidities (0, 50, 100, 150 NTU), contact times (CT: 3 or 5 minutes), and bacterial concentrations of EHEC, SM, or LM at 6 and 3 log CFU/mL per EPA 2020 guidelines. Treatments that achieved a 3-log reduction of the selected organisms within a 5-minute contact time, with no viable cells after enrichment, were considered the most effective and exceeded EPA requirements. These treatments were then evaluated for their corrosion capacity on stainless steel (SS304, SS316) and aluminum (AL3004) coupons, as well as their effects on soil and plant health (romaine lettuce) under greenhouse conditions. Chlo at 60 ppm, SAS at 0.60%, and PAA at 30 ppm achieved a 3-log reduction, with no viable cells after enrichment, for all strains after a 5-minute contact time (P<0.05). The corrosion capacity for the most effective treatments was tested at 14-day intervals at 23°C and 73°C for stainless steel (SS304, SS316) and aluminum (AL3004) coupons submerged in each sanitizer solution. There was no significant difference in corrosion between SS304 and SS316 (P<0.05). AL3004 showed greater corrosion than SS, with the highest rate observed at 0.6% SAS (4.52E-02 cm/year). Greenhouse-grown romaine lettuce was spray-inoculated with a bacterial cocktail of LM/EHEC at 5 log CFU/mL. Bacterial recovery was performed at 0-, 4-, 8-, and 12-days post-inoculation using selective-differential media. Soil samples were collected from treated and non-treated samples to assess soil chemical and physical properties. Bacterial inactivation had a negative correlation with water turbidity and a positive correlation with contact time and sanitizer concentration (P<0.05). In the greenhouse trial PAA, Chlorine and SAS exhibited a higher bacterial reduction compared to a water-control, with marginal differences in reduction between sanitizers (P<0.05). The highest reduction was achieved by PAA (0.98 log CFU/gram-lettuce) reduction compared to the water control. SAS exhibited phytotoxicity in the lettuce leaves in the second greenhouse trial. All sanitizers caused marginal changes in the overall properties of soil physical and chemical properties, with sodium and electrical conductivity being the main factors affected by the constant application of each sanitizer.
Open Access
Characterizing controls of sorghum carotenoid bioaccessibility for vitamin A biofortification
(Colorado State University. Libraries, 2024) McDowell, Rae, author; Rhodes, Davina, advisor; Morris, Geoff, committee member; Chaparro, Jacqueline, committee member
Vitamin A deficiency is one of the leading causes of preventable blindness globally and can lead to decreased immune function and mortality. Sorghum bicolor is consumed in areas that are affected by vitamin A deficiency, where biofortification of sorghum may be a way to address these nutritional deficiencies. However, sorghum breeders do not know the target breeding value for provitamin A carotenoids or the best breeding strategy for carotenoid biofortification. Bioaccessibility—the amount of a nutrient available to be absorbed in the gut—can be reduced by a variety of factors, and needs to be determined in order to define a biologically relevant target value of provitamin A carotenoids. Additionally, genetic controls of grain bioaccessibility need to be determined in order to develop breeding tools. This research sought to develop biofortification breeding strategies by characterizing the environmental and genetic controls of carotenoid bioaccessibility through genomic mapping and multi-environment trials. We hypothesized that 1) genotype has a greater impact on variation in carotenoid bioaccessibility than genotype by environment interactions, and 2) carotenoid bioaccessibility is an oligogenic trait. To test these hypotheses, twelve sorghum genotypes were grown across three climates (semi-arid, humid-subtropical, and humid-continental) for two years. Results suggest there is a strong environmental and genotype by environment interaction in the regulation of bioaccessibility of sorghum carotenoids. One environmental factor that may contribute to variation in bioaccessibility is iron and zinc content, which was found to have a significant negative correlation with carotenoid bioaccessibility traits. Next, genome-wide association studies (GWAS) in a diverse population and linkage mapping in a F5.6 recombinant inbred family identified a handful of genes or regions underlying variation in carotenoid bioaccessibility and carotenoid content, supporting the hypothesis that there are oligogenic controls. GWAS revealed two significant marker trait associations (MTAs) underlying relative bioaccessibility of ɑ-cryptoxanthin and cis-β-carotene on chromosomes five and one respectively. Furthermore, in the inbred family, there were observations of transgressive segregation, in which a portion of the progeny exceeded parental means for both carotenoid content and bioaccessibility. Additionally, linkage analysis identified six unique regions for carotenoid content and three unique regions for carotenoid bioaccessibility, further supporting the oligogenic hypothesis for genetic architecture. Linkage analysis also revealed colocalization of regions between carotenoid content and carotenoid bioaccessibility, either suggesting co-regulation or linkage between traits. Interestingly, several a priori candidate genes in proximity to identified MTAs and linkage regions were broadly involved in carbohydrate, lipid, and carotenoid metabolism. These results will help refine the carotenoid biofortification target value and lead to the development of molecular breeding tools that can be used to increase carotenoid content and bioaccessibility, as well as to maintain favorable alleles, in sorghum breeding germplasm.
Open Access
Evaluating leafy green production in a Colorado rooftop agrivoltaic system
(Colorado State University. Libraries, 2024) Villa-Ignacio, Armando, author; Bousselot, Jennifer, advisor; Uchanski, Mark, committee member; Sampath, Walajabad, committee member
Combining green roofs with solar modules can protect plants and produce energy in cities. Growing crops in this system is called rooftop agrivoltaics (RAV) and can complement current urban agriculture efforts. We evaluated a group of five leafy green crops (arugula, kale, lettuce, spinach, and Swiss chard) under different solar modules over two years at two locations. Data measurements were taken for fresh and dry weight (FW, DW) stomatal conductance (SC), plant size at harvest (PSH), and microclimate data. At the Colorado State University Foothills Campus, the treatments included a polycrystalline opaque silicon module, a cadmium telluride (CdTe) frameless opaque module, and a 40% semi-transparent CdTe module. At CSU Spur, there was an opaque module and a bifacial module. Both sites included a full sun control plot. At the Foothills campus, for of the five leafy greens produced higher FW and DW under the 40% semi-transparent modules compared to other treatments and the full sun control, except spinach. Most species also produced larger PSH under the PV module treatments compared to the full sun control. Leafy greens under the module treatments resulted in lower SC, however, lettuce and Swiss chard grown under the semi-transparent module treatment produced higher SC compared to all other treatments. At CSU Spur, plant responses were also species specific with arugula, kale, and lettuce yielding higher FW and DW in full sun. Most leafy greens resulted in lower SC, except for lettuce, which had a higher SC under solar module treatments. Spinach had no difference in FW but lower DW in the opaque treatment compared to the full sun control, and lower SC under both treatments. There was a lower FW between the bifacial treatment and the full sun control in Swiss chard. This research shows that incorporating photovoltaics on rooftop gardens influences the yield and stomatal conductance of select leafy green crops. While FW and DW mostly decreased under the deep shade treatments (opaque module, frameless module, and bifacial module) SC decreased, possibly due to less solar radiation on the leafy greens, reducing water use. Understanding the growth characteristics and growing environment of high value crops like leafy greens will increase understanding of what food crops are suitable for RAV systems.
Embargo
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.
Embargo
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.
Open Access
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.