Browsing by Author "Ward, Sarah M., committee member"

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Open Access
A study of plant domestication and evolution through the taxonomic revision of wild North American Humulus, a phytochemical assay for stimulant alkaloids in Celastraceae, and a phylogeographic analysis of Catha edulis in areas of historic cultivation
(Colorado State University. Libraries, 2015) Tembrock, Luke Raymond, author; Simmons, Mark P., advisor; Angert, Amy L., committee member; Richards, Christopher M., committee member; Ward, Sarah M., committee member
The cultivation of plant species is essential to the survival of humans. The process of artificial selection that is used to modify wild individuals into improved cultivars results in genetic and morphological changes from wild progenitors. In order to understand the evolutionary patterns and processes involved with artificial selection both wild and cultivated populations must be thoroughly studied. Numerous methods are used to study the process of evolution under cultivation such as biology, chemistry, geography, history, linguistics and archeology. The understanding of evolution in a crop species is essential in current improvement programs to increase yield for a given crop. I employed methods from the fields of taxonomy, analytical chemistry and phylogeography to study the process of evolution in cultivated plant species and/or their wild relatives. From a review of taxonomic, genetic, and phytochemical literature, as well as examination of morphological features I revised the wild North American Humulus (Cannabacae) in a manner that properly delimits the diversity found among the North American species. Using GC–MS and a forensics based derivatization method I assayed for the stimulant alkaloids cathinone, cathine, and similar compounds across the Celastraceae plant family. It was found that that qat (Catha edulis) was the only species of those tested that biosynthesized cathinone and cathine. Using phylogeographic and population genetic techniques I inferred three wild regional origins, hybridization and numerous translocations out of the centers of origin for cultivated qat. From farmer interviews I examined what properties, genotype, phenotype, and/or geography explained the naming convention for qat cultivars among qat farmers. The character of stem color was found to highly plastic and thus genotype was not significantly correlated with the naming convention. Geographic patterns were confirmed for several cultivar names suggesting that anthropogenic factors are important in the naming conventions used among qat farmers. These four separate studies provide findings that not only clarify our understanding of evolutionary patterns among wild and cultivated species but provide a framework for breeding, conservation and forensic applications in the future.
Open Access
Effects of elevated plant selenium levels on reproduction and root-nematode interactions
(Colorado State University. Libraries, 2011) Prins, Christine N., author; Pilon-Smits, Elizabeth A. H., advisor; Ward, Sarah M., committee member; Bedinger, Patricia A., committee member
Selenium is an important element in soils throughout the western United States, and its presence has important consequences for the ecology of these seleniferous sites. Some plants in seleniferous areas have evolved mechanisms to hyperaccumulate Se to 0.1 - 1% of their dry weight. Other plants accumulate moderate Se levels between 0.01 - 0.1% of their dry weight. In the studies described in this thesis, facets of the evolution of Se accumulation and the associated ecology of Se hyperaccumulators are considered. First, I examined the effect of increasing Se on reproductive parameters of Se accumulators and hyperaccumulators. The reproductive parameters were measured through cross-pollinations of greenhouse-grown accumulator plants receiving different Se concentrations. In the accumulator Brassica juncea , increasing Se concentrations in plant tissues caused decreases in biomass, pollen germination, seed weight, seed production, and seed germination. In some cases, however, interactions of similar Se concentrations in both parents actually proved beneficial to reproduction. The hyperaccumulator Stanleya pinnata showed no effect of increased Se concentration on pollen germination. These data provide interesting insight into the potential reproductive cost of Se accumulation, and the apparent evolution of physiological tolerance mechanisms in hyperaccumulators to avoid these reproductive problems. To further investigate the effect of Se on reproduction, S. pinnata plants were taken to a field site with hives of the European honey bee (Apis mellifera) to examine the effect of Se in floral tissues on potential pollinators. The bees and other pollinators showed no preference for or against Se in the flower and foraged on both high- and low-Se plants equally. Because the bees showed no preference, the honey of bees in seleniferous sites was analyzed for the presence of Se, and there were small amounts (up to 2 mg kg-1 FW) of Se found in this honey. These findings are important for bee keepers in seleniferous areas, as they show no evidence of toxic Se levels in their honey and they may even market their honey as Se-enriched and beneficial for human health. The finding that bees do not discriminate between high and low-Se plants does warrant further studies on the potential health effects of the ingested Se on the pollinators and the movement of Se into the food chain. Next, to further investigate the ecology of Se hyperaccumulators, I examined the interactions of hyperaccumulator roots with root-associated nematodes. Selenium hyperaccumulators S. pinnata and Astragalus bisulcatus growing in the field have root Se concentrations between 100 and 1,500 mg Se kg-1 DW, a toxic concentration to most above-ground herbivores. Therefore, it was expected that with increasing root Se concentrations, there would be reduced levels of nematodes associated with plants. There was no significant negative correlation with increasing Se concentration, and even roots containing >1,000 mg Se kg-1 Se harbored nematode herbivores. However, when nematodes extracted from field-harvested plants were used to inoculate greenhouse-grown S. pinnata , plants treated with Se did harbor significantly fewer nematodes several months later. These findings are of significance, both because they suggest the presence of Se-tolerant and potentially Se-specialist nematodes in seleniferous sites, and for the possible use of Se as a pesticide for nematodes in non-seleniferous sites. Furthermore, the roots of hyperaccumulators were examined for the spatial distribution and speciation of Se using X-ray Absorption Spectroscopy (XAS). The majority of the Se was found in the cortex and epidermis of the root, with lower levels in the wood. Organic Se of the C-Se-C type (Se bonded to two carbon atoms, similar to methyl-selenocysteine) was the predominant form of Se in the hyperaccumulator roots, together with a small fraction of inorganic selenite. The findings presented in this thesis may also have relevance for hyperaccumulators of other elements, such as arsenic, cadmium, nickel or zinc, as these metals may also protect roots from nematodes and other root herbivores, and may have similar effects on reproduction. Further investigations may reveal other herbivores that are deterred by root hyperaccumulation, as well as more evidence of specialist herbivores that have evolved tolerance in response to the hyperaccumulator's elemental defense. Beyond insight into the ecological and co-evolutionary relationships between roots and herbivores, the results presented here also have applications in agriculture. Since Se is both a nutrient and a toxin, depending on its concentration, Se could be used as an alternative to organic pesticides in controlling root nematode and herbivore levels in organic and subsistence farming. With careful monitoring, the resulting plants may be considered Se-fortified food with enhanced nutritional value. Finally, the findings presented here provide a framework for follow-up studies investigating the evolution of plant Se hyperaccumulation and the associated effects of (hyper)accumulated plant Se on ecological interactions in seleniferous habitats.
Open Access
Examining the unpredictable nature of yellow toadflax
(Colorado State University. Libraries, 2011) Krick, Nicholas Jon, author; Beck, Kenneth George, advisor; Nissen, Scott Jay, committee member; Ward, Sarah M., committee member; Meiman, Paul J., committee member
Yellow toadflax (Linaria vulgaris Mill.) is an aggressive creeping perennial forb that was introduced to North America in the 1600's. It is now naturalized throughout the United States and Canada and is a serious weed in the Intermountain West. This plant threatens cropping systems, rangelands, and natural areas. Colorado State University Weed Science has conducted research on yellow toadflax control for more than 20 years yielding variable and inconsistent results. Short term success has been achieved; however, recommendations for acceptable long term control are unavailable. Dramatic site-to-site variation has been observed, but the source of that variation has not been determined. Yellow toadflax is an obligate outcrossing species that exhibits much genetic and phenotypic variation and may inhabit a wide range of ecosystems. The success of managing yellow toadflax might hinge on application timing; therefore, an observational study of root bud phenology was conducted for 2 years at two sites in Colorado. This study showed that yellow toadflax exhibited a pattern of root bud development and that pattern had an important relationship to flowering. Root buds were present throughout the growing season, but their numbers fluctuated. Following bud emergence in the spring, bud numbers declined until they reached their lowest counts around the full bloom/seed set growth stage. Following this growth stage, bud numbers increased suggesting the root system was a demanding carbohydrate sink. This observational study supported results from herbicide field trials. Identical herbicide efficacy trials were conducted at five separate locations in Colorado where four rates of chlorsulfuron and imazapyr were each applied in September 2008. Plants were harvested from these same sites and were subjected to a common garden experiment and an ALS enzyme bioassay. Analysis of field experiments 1 year after treatment (1 YAT) showed site variation using low herbicide rates (40 g ae ha-1 chlorsulfuron and 127 g ae ha-1 imazapyr), but most variation was overcome by increasing herbicide rates. Chlorsulfuron applied at 94 g ae ha-1 controlled more than 76% of yellow toadflax at all sites; whereas, 380 g ae ha-1 of imazapyr was necessary to overcome site to site variation, but control was ≥73% at four of five sites. Evaluations 2 YAT showed that yellow toadflax recovered at two sites. The common garden study and ALS enzyme bioassay revealed that these populations were susceptible to herbicides on a whole plant level and on a mechanistic level; confirming that herbicide resistance is not responsible for spatial variation. It appears that yellow toadflax recovery was largely driven by length of growing season and the growth stage of a population at which applications occurred. Lower elevation sites had a higher percentage of shoots flowering at the time of application and were more difficult to control. Comparing results from the field experiments to the pattern of root bud development, applications at the lower elevation sites occurred when bud numbers were decreasing or at their lowest counts. Higher elevation sites were in a more advanced growth stage, which resulted in better control likely based on the phenology of root bud development. It is likely that more buds present or developing on a plant resulted in better control because bud are strong sinks and herbicides were likely translocated to those tissues and had a greater negative effect on their root systems. Managers can utilize what has been learned though these experiments to improve their programs and management success. Management can be improved by increasing herbicide rate, but more importantly by targeting populations at their most susceptible growth stage. Although a rate increase of herbicide is necessary to overcome site variation, this should result in less overall herbicide use (decrease due to fewer tank mixes, fewer application events, and elimination of high rates of ineffective compounds), reduced costs for managers, and will decrease environmental exposure to herbicides.
Open Access
Genetic variation among inland and coastal populations of Distichlis spicata sensu lato (poaceae) in the western United States
(Colorado State University. Libraries, 2010) Harrington, Judith Eileen, author; Brick, Mark A., advisor; Black, William C., IV, committee member; Panella, Leonard W., committee member; Ward, Sarah M., committee member
The taxonomic status of the North American endemic grass Distichlis spicata subsp. striata has been in flux for more than a century. Distichlis spicata hosts the larval stage of a federally endangered butterfly and is being investigated for use in restoration and recreation, so the relationship between the species and its subspecies merits clarification. Although the subspecies stricta was once recognized as a species {Distichlis stricta), most current treatments either consider it an inland subspecies within Distichlis spicata or decline to recognize it at all. Two recent studies did not find genetic or morphological evidence differentiating the subspecies stricta from Distichlis spicata. Genetic variation among 13 coastal and inland populations of Distichlis spicata sensu lato was characterized using chromosome counts, chloroplast DNA segments, microsatellite alleles, RAPD bands, and DNA C-values. Plants grown in a common garden were evaluated for date of first flowering. The results suggest the existence of two genetically segregated lineages that differ for chromosome number, molecular sequences in cpDNA and nuclear DNA, DNA C-value, and flowering time. One lineage has a somatic chromosome number of 2n = 40 and encompasses plants from the West Coast and several inland locations in Nevada, Utah, and southern New Mexico. The other lineage has a somatic chromosome number of 2n = 38 and consists of plants distributed only inland among the populations surveyed. Genetic distances among populations were closer within each lineage than between the two lineages, even when different lineages occurred in geographic proximity. The 38-chromosome lineage should be recognized as a distinct species corresponding to the previously recognized Distichlis stricta. The 40- chromosome lineage is Distichlis spicata.