Graduate Thesis Or Dissertation
 

Gene flow from transgenic glyphosate-resistant creeping bentgrass (Agrostis stolonifera L.) at the landscape level

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  • Creeping bentgrass (Agrostis stolonifera L.) is an outcrossing, small- seeded, perennial grass that can establish outside of cultivation and has several compatible relatives. Glyphosate is a nonselective, broad spectrum, herbicide. Transgenic glyphosate-resistant (GR) creeping bentgrass (GRCB) was developed by The Scotts Company and Monsanto, but is still under USDA-APHIS regulated status. In 2002, 162 ha were planted to GRCB within a 4,500 ha control area north of Madras, OR, and produced seed in 2003. After a wind event moved swathed panicles off the GRCB fields, the fields were taken out of production and a mitigation program was initiated. The goal of this study was to assess the potential of gene flow from GRCB at the landscape level. A four-year survey was conducted in situ to determine the proportion of GR plants established outside of cultivation. Evidence of gene flow was found in all years. In 2006, despite the ongoing mitigation program, 62% of the 585 creeping bentgrass plants tested in situ were GR. Panicles were collected from Agrostis spp. and rabbitfoot grass (Polypogon monspeliensis (L.) Desfontaines) plants for the four years. Seedlings produced were screened in the greenhouse using glyphosate to assess the occurrence of pollen-mediated gene flow. Gene flow via pollen was found in all four years. A set of chloroplast microsatellite (cpSSR) markers and a matK indel marker were developed to aid in the identification of Agrostis spp. and potential hybrids. Chloroplast markers were used in combination with nuclear ITS sequence to confirm transgenic interspecific and intergeneric hybrids produced in situ. The effect of soaking time and water temperature on seed germination potential was studied to explore the potential of seeds-mediated gene flow in time and space. Creeping bentgrass seeds did not lose their germination after 17 wk in water at 20 C and germination was 46% after 17 wk at 4 C. Panicles were found to travel in an irrigation canal at an average rate of 19 ± 1 m min-1. Results of this study should be used in the decision making process for authorization of field trials and deregulation of transgenic crops, especially grasses.
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