Theses and Dissertations
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Browsing Theses and Dissertations by Author "Argueso, Cris, committee member"
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Item Open Access Detecting durable resistance to rice bacterial blight(Colorado State University. Libraries, 2016) Delorean, Emily Elizabeth, author; Leach, Jan, advisor; Verdier, Valerie, committee member; Argueso, Cris, committee member; Brick, Mark, committee memberThe productivity of rice, a staple crop worldwide, is limited by pathogens such as Xanthomonas oryzae pv oryzae (Xoo). Controlling yield loss to the resulting disease, bacterial blight, is most effective through growing genetically pathogen resistant rice varieties. However, widespread deployment of varieties containing single gene resistance to bacterial blight places an immense selection pressure on Xoo to evolve virulence. The major virulence factors employed by Xoo to drive infection are transcription activator like (TAL) effectors. TAL effectors are secreted into the host cells where they target the transcription of particular host susceptibility genes to favor infection. Previous TAL effector research indicates that not all TALs are created equal and some are crucial to the virulence of Xoo. By breeding for resistance genes targeting necessary TAL effectors we may find more durable resistance as selection pressure on the pathogen will result in loss of the TAL effector function and therefore a decrease in virulence and pathogen fitness. In the present study, we characterized a novel and widespread TAL effector through quantitative trait loci (QTL) mapping. We used the indica rice Multi-Parent Advanced Generation Inter-Cross (MAGIC) population to screen for resistance to the cloned TAL effector, TAL7b, and the Philippine race 6 Xoo strain PXO99A. Our results confirm that TAL7b is a virulence enhancing factor and that the MAGIC population contains six loci targeting resistance to TAL7b.We also identified another seven resistance QTL to the highly virulent Xoo strain, PXO99A.Item Open Access Information on emergent insect associated tree diseases including epidemiological studies of drippy blight disease of oak and thousand cankers disease of walnut(Colorado State University. Libraries, 2017) Sitz, Rachael A., author; Cranshaw, Whitney, advisor; Stewart, Jane, advisor; Argueso, Cris, committee member; Koski, Tony, committee memberTwo emergent disease complexes called drippy blight and thousand cankers have become injurious to hardwood trees in communities across the urban corridor of Colorado. In order to better understand these disease complexes, studies were initiated to identify the causal agents, symptomology, and epidemiology of drippy blight disease as well as determine if multiple fungi were involved in thousand cankers disease. Chapter I, published in the Journal of Arboriculture and Urban Forestry, provides information on the basic biology of drippy blight disease. This article explains the signs and symptoms of drippy blight, and shows that the bacterium Lonsdalea quercina subsp. quercina is able to cause the disease. Finally, it was noted that a kermes scale insect was abundant on all diseased oaks, but its role as a vector is unknown. Overall, this research documents the microbe and insect causal agents in this disease complex. These findings are biologically significant as the isolated bacterium was able to produce disease on several species of sapling red oaks. This, taken into consideration with other diseases caused by Lonsdalea quercina, implies that this bacterium has the potential to become widespread. Chapter II provides a detailed life history of Allokermes galliformis, the insect causal agent in drippy blight disease. Management decisions to mitigate the effects of insect damage are largely based on an understanding of the life cycle. This research documents periods when A. galliformis may be most exposed and vulnerable to controls and notes areas of the tree where it inflicts damage when feeding. Therefore, the information provided in this chapter can serve as a guide for more informed decisions when considering management of drippy blight-affected trees. Chapter III considers what insects may be involved in the dissemination of Lonsdalea quercina subsp. quercina from oaks with symptoms of drippy blight disease. Although kermes scales are the most consistent and abundant insects found in association with drippy blight disease, other more mobile insects are frequently observed on diseased trees and it was hypothesized that these may play a role in spreading the bacterial pathogen within trees and to new trees. After testing insects collected on diseased oak trees for bacterial contamination, various insects were documented to carry the bacterium, providing insight into ways the disease may move in a population of susceptible hosts. Chapter IV, published in Plant Disease, involves a tree disease characterized by an insect and fungal pathogen interaction, thousand cankers disease of walnut. This study investigates whether genetically distinct isolates of the fungal pathogen Geosmithia morbida vary in pathogenicity. Also examined was whether Fusarium solani, commonly found on diseased trees, may contribute to production of thousand cankers disease. A range of Geosmithia morbida isolates were tested alone and in combination with a Fusarium solani isolate to determine the relative contribution of each fungal pathogen to thousand cankers disease. Importantly, in Colorado Geosmithia morbida does not interact synergistically with F. solani. Overall, this research is the first to describe the emergent disease complex drippy blight and provides information to better understand the bacterial and insect causal agents. Furthermore, the investigations of drippy blight of red oak and thousand cankers disease of walnut, improve our understanding of the epidemiology of woody plant diseases that involve both arthropod and pathogen partners.Item Open Access Phenotypic plasticity in the response of sorghum to water stress and recovery indicates pre-flowering drought tolerance(Colorado State University. Libraries, 2018) Miller, Sarah Bethany, author; Jahn, Courtney, advisor; Argueso, Cris, committee member; Broeckling, Corey, committee member; Leach, Jan, committee memberTo view the abstract, please see the full text of the document.