Surveying of pollen-mediated crop-to-crop gene flow from a wheat field trial as a biosafety measure

Outcrosses from genetically modified (GM) to conventional crops by pollen-mediated gene flow (PMGF) are a concern when growing GM crops close to non-GM fields. This also applies to the experimental releases of GM plants in field trials. Therefore, biosafety measures such as isolation distances and surveying of PMGF are required by the regulatory authorities in Switzerland. For two and three years, respectively, we monitored crop-to-crop PMGF from GM wheat field trials in two locations in Switzerland. The pollen donors were two GM spring wheat lines with enhanced fungal resistance and a herbicide tolerance as a selection marker. Seeds from the experimental plots were sampled to test the detection method for outcrosses. Two outcrosses were found adjacent to a transgenic plot within the experimental area. For the survey of PMGF, pollen receptor plots of the conventional wheat variety Frisal used for transformation were planted in the border crop and around the experimental field up to a distance of 200 m. Although the environmental conditions were favorable and the donor and receptor plots flowered at the same time, only three outcrosses were found in approximately 185,000 tested seedlings from seeds collected outside the experimental area. All three hybrids were found in the border crop surrounding the experimental area, but none outside the field. We conclude that a pollen barrier (border crop) and an additional isolation distance of 5 m is a sufficient measure to reduce PMGF from a GM wheat field trial to cleistogamous varieties in commercial fields below a level that can be detected.