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Browsing by Author "Gaines, Todd A., author"

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    Assessing genetic diversity and phenotypic plasticity in Cirsium arvense: evaluation with greenhouse trials and ISSR
    (Colorado State University. Libraries, 2004) Gaines, Todd A., author; Brown, Cynthia S., author; Hufbauer, Ruth A., author
    Invasive plant species cause damage to ecosystems and economic loss to land managers. One particularly invasive plant species is Canada thistle (Cirsium arvense). This plant is very difficult to control and is a successful invader in many diverse ecosystems, including cropping systems and non-cultivated lands. If C. arvense is successful because it has adapted genetically to new environments, then these differences may be quantified using experimental observations. The objective of this project is to quantify genetic diversity and site-specific genetic differentiation based on phenotypic responses in common garden trials. Canada thistle specimens from crop and non-crop habitats in two different biogeographic regions of Colorado were used. A second objective is to correlate data from genetic markers with phenotypic data to further quantify genetic diversity in specimens from crop and non-crop habitats in three different regions of Colorado. The greenhouse experiments compared the phenotypic responses of the collected plants to variations in soil fertility and water stress. Leaf tissue DNA collected from the sites was amplified with the inter-simple sequence repeat (ISSR) method and the resulting banding patterns were analyzed for genetic variation. Data from the greenhouse trials indicate a greater response to treatments only in Larimer County non-crop populations. Data from genetic analyses indicate a high level of diversity in the sampled genomes. These data are consistent with the invasive characteristics of C. arvense but indicate that Colorado populations have not genetically differentiated within the sampled ecosystems. More study is warranted to further investigate this question.
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    Molecular genetics of glyphosate resistance in Palmer amaranth (Amaranthus palmeri L.)
    (Colorado State University. Libraries, 2009) Gaines, Todd A., author; Westra, Philip, advisor; Leach, Jan, advisor
    Glyphosate resistant Palmer amaranth populations were identified in Georgia in 2004. Studies were undertaken to characterize inheritance, the molecular basis of resistance, and the potential for gene transfer to related Amaranthus species. Dose response results support rejecting a monogenic inheritance hypothesis in favor of an alternative polygenic, additive inheritance model. Apomixis in genetic populations used for inheritance studies is probably occurring and makes interpretation of inheritance difficult. Glyphosate resistance in Palmer amaranth appears to be incompletely dominant and may be polygenic. No target site mutations known to confer resistance were identified in resistant alleles of the 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) gene, the target of glyphosate. Estimation of gene copy numbers of EPSPS relative to acetolactate synthase (ALS) in gDNA by quantitative PCR (qPCR) suggested that resistant plant genomes contain 64 to 128 times more copies of EPSPS than susceptible plants. qPCR on cDNA revealed that EPSPS was expressed approximately 35 times higher in resistant plants. Elevated EPSPS copy number is heritable and correlates with expression level and resistance in F2 populations. The molecular basis of resistance is likely due to increased production of EPSPS due to gene amplification. This is the first documented occurrence of EPSPS gene amplification in a weed population under glyphosate selection pressure. The risk of resistance gene transfer was measured with field studies and hand crosses with A. hybridus, A. retroflexus, A. powellii, A. spinosus, and A. tuberculatus. Glyphosate application (0.4 kg ha-1) was used to screen for resistant progeny from the crosses. Hybridization with A. spinosus occurred in both years of the field study and in hand crosses, with average frequency ranging from <0.01% to 1.4%. Hybrids with A. spinosus were either monoecious or dioecious. Monoecious plants produced seed through self-pollination, and the F2 progeny were segregating for resistance. Hybridization occurred in the 2007 field study with A. hybridus (<0.01%) and A. tuberculatus (0.08% and 0.19% for two accessions), all of the hybrid plants were dioecious, and none produced seed. The highest risk for glyphosate resistance gene transfer from A. palmeri is to A. spinosus.