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Title: Occurrence of transgenic feral alfalfa (Medicago sativa subsp. sativa L.) in alfalfa seed production areas in the United States

Author
item Greene, Stephanie
item KESOJU, SANDYA - Washington State University & Henan Agricultural University
item Martin, Ruth
item Kramer, Matthew

Submitted to: PLOS ONE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/3/2015
Publication Date: 12/23/2015
Citation: Greene, S.L., Kesoju, S., Martin, R.C., Kramer, M.H. 2015. Occurrence of transgenic feral alfalfa (Medicago sativa subsp. sativa L.) in alfalfa seed production areas in the United States. PLoS One. 10(12):e0143296. doi:10.1371/journal.pone.0143296.

Interpretive Summary: Genetically-engineered glyphosate-resistant alfalfa (Medicago sativa subsp. sativa) was commercialized in 2011. The potential risk of transgene dispersal into the environment is not clearly understood for alfalfa, a perennial crop that is cross-pollinated by insects. We gathered data on feral and transgenic feral alfalfa in major alfalfa seed production areas in the western United States and examined factors that may explain occurrence. Of 4632 sites surveyed, feral plants were observed at 404 sites. Twenty six percent of these sites had transgenic plants. Feral populations appeared to occur independently, and tended to cluster in seed and hay production areas, places where seed tended to drop. In some instances, feral plants appeared to colonize nearby locations. There was some evidence that populations were self-sustaining although further research is needed to confirm. Gene flow among feral populations was likely, since average nearest neighbor distance among feral sites was well within pollinator forage range. Locations of feral plant clusters were not well predicted by the environmental or production variables examined. However, the locations of transgenic feral populations were consistently found where seed escape was high; either adjacent to original GE seed fields or on roads used to transport seed to conditioning plants. Our study illustrates the challenge of preventing transgene dispersal into the environment.

Technical Abstract: Genetically-engineered glyphosate-resistant alfalfa (Medicago sativa subsp. sativa) was commercialized in 2011. The potential risk of transgene dispersal into the environment is not clearly understood for alfalfa, a perennial crop that is cross-pollinated by insects. We gathered data on feral and transgenic feral alfalfa in major alfalfa seed production areas in the western United States and examined factors that may explain occurrence. Road verges in California, Idaho and Washington were surveyed in 2011 and 2012 for feral plants and leaf and seed samples were tested for the CP4 EPSPS protein that conveys resistance to glyphosate. Demographic surveys of feral populations were conducted in 2013. Spatial statistics and generalized linear models were used to examine spatial patterns and influence of climate, topography, cropping pattern, roadside habitat and proximity to historic GE alfalfa hay and seed fields, on the occurrence of feral and transgenic feral plants. Of 4632 sites surveyed, feral plants were observed at 404 sites. Twenty six percent of these sites had transgenic plants. Spatial analysis suggested that feral populations started independently, and tended to cluster in seed and hay production areas, places where seed tended to drop. Significant but low spatial auto correlation suggested that in some instances, plants could colonize nearby locations. Nearly half the populations had mixed-aged cohorts, indicating some feral populations were self-sustaining. Gene flow among feral populations was likely, since average nearest neighbor distance among feral sites was well within pollinator forage range. Locations of feral plant clusters were not well predicted by the variables examined. However, the locations of transgenic feral populations were consistently found where seed escape was high; either adjacent to original GE seed fields or on roads used to transport seed to conditioning plants. Our study illustrates the challenge of preventing transgene dispersal into the environment.