Transgene Movement in Commercial Alfalfa Seed Production: Implications for Seed Purity.

Alfalfa was the first perennial crop genetically engineered (GE) to resist glyphosate herbicide and was initially deregulated in 2006, and again in 2011. The potential for gene flow has been widely recognized since alfalfa is largely out-crossing and is insect-pollinated. The United States (especially western U.S.) is a major exporter of alfalfa seed and hay and the organic dairy industry is one of the fastest growing agricultural sectors. Because of this, many alfalfa producers are impacted by market sensitivity to adventitious presence (AP) of GE traits. Our objective was to quantify the extent of transgene movement from GE seed fields to conventional seed fields on a landscape level, to define GE pollen dispersion curves based on the spatial distribution of commercial seed fields, and to provide industry with information to support coexistence strategies.  In spring (2013), alfalfa seed and hay fields were mapped in the Touchet Valley, Walla Walla County, WA. GE seed fields (source fields) and 14 conventional seed fields (sink fields), located at various distances from GE sources, were identified. Sink fields were combine and hand harvested along field edges every 30 m and within fields for every 15 m. Parent seed lot and overall bulked samples of the 2013 harvest were obtained for sink fields for baseline and overall AP assessment. Distance from GE seed fields, distance from alkali bee bed, elevation, aspect, and slope were also obtained. A seedling germination assay was developed to quantify level of AP. AP (%) and baseline AP (%) were transformed to proportions and nonlinear regression was applied to the data. A significant negative relationship was found between GE seed fields and level of AP found in conventional seed fields. No relationship was found between alkali bee bed, elevation, slope, aspect, and level of AP in conventional fields. AP in conventional fields declined, as the source fields were located further from conventional fields. Pending completion of the analysis, further results will be presented.