Gene Flow from GE Seed Fields and Feral Plants: Implications for Genetic Purity in Conventional Seed Fields.

Genetically engineered traits provide alfalfa producers with new tools to support profitable production. But due to alfalfa’s propensity for gene flow and risk of adventitious presence (AP), these new tools need to be deployed carefully to preserve a grower’s ability to produce for AP-sensitive markets. Feral populations with population density have a great influence on pollen-mediated gene flow, with implications for genetic purity. The dependence on insects for pollination makes pollen-mediated gene flow a common phenomenon in this species. However, pollen is not the only source of gene flow as seed-mediated gene flow is also a concern. Our objective was to determine gene flow from GE seed fields and feral plants to conventional seed fields and to determine if the plants become established. Alfalfa feral populations and seed fields were mapped in the Fresno County, CA in spring 2013. GE seed fields and feral plants (source) and conventional seed fields (sink fields), located at various distances from GE sources, were identified. Conventional seed fields were combine and hand harvested along field edges every 30 m. Leaf samples (169 samples) were collected from all the 4 edges of conventional seed field nearby GE seed field (grown in 2005-2007). Original samples (seed used to plant the fields in 2013) were collected for initial assessment of AP and for determining baseline contamination if any. For fields where no original seed sample was produced, leaf samples were collected instead to determine baseline AP. Harvested samples were threshed, cleaned, scarified, and tested for the transgene using seedling germination assay. Distance from GE seed fields, distance from glyphosate-resistant feral plants, pollinator abundance, elevation, aspect, and slope were also obtained. The relationship between AP proportion and distance to GE source fields will be modeled using nonlinear models. No AP was observed in conventional seed fields located nearby glyphosate-resistant feral plants suggesting there is less likely for gene flow to occur. Out of 169 leaf samples collected from conventional seed field grown next to GE seed field (2005-2007), 3 samples showed transgene presence in 2013 suggesting that transgenic alfalfa can get established. Pending completion of the analysis, further results will be presented.