Gene Flow from GE to Conventional Maize in Real Situations of Coexistence

maize fields coexisted with other crops. Both regions are characterized by small size of the fields (0.5-5 ha, with a mean of about 2 ha). In both regions, two areas were defined: the central area in which conventional fields were selected for sampling; and the surrounding area that may influence rate of pollen-mediated gene flow. The total surface area studied in Térmens was 300 ha, with a central area of 43 ha; whereas in Pla de Foixà the area was 400 ha, with a central area of 100 ha. An aerial view of some fields from Foixà area is shown in Figure l. The different crops (cereals, fruit trees, maize, etc.) were identified during the cropping season, and data on maize cultivar, sowing and flowering dates, and wind speed and orientation were recorded. All of these data were used to choose the non-transgenic fields for sampling. At harvest, samples were collected and analyzed by real-time quantification system-polymerase chain reaction (RTQ-PCR) as described in Pla et al., 2006. Five conventional fields in the Térmens area and seven in the Foixà area were chosen to detect and quantify the rate of cross- fertilization. In the Térmens area, fields were analyzed for both Mon810 and Bt176 events; whereas, in the Foixà area, analysis was performed for the Mon810 event only, because neither the fields of the selected zone nor the fields of the surrounding zone had been sown with Bt176 maize. A stratified sampling system was applied by dividing fields into different zones according to the distance from the borders. The number of sampling points for each border depended on the size and particular shape of the field. In total 488 analyses were performed.