From 2000-2003 a range of Farm Scale Evaluation (FSE) trials were established in the UK to assess the effect of the release and management of herbicide tolerant (HT) crops on the abundance and diversity of farmland wildlife compared with their conventionally managed non-GM-equivalents. The objective of this research project was to investigate gene flow within the winter (WOSR) and spring oilseed rape (SOSR) FSE trials and to develop a statistical model for the prediction of cross-pollination frequency that can be used to evaluate current separation distance guidelines. Seed samples were collected from the non-GM half of the trial sites and were tested for evidence of cross-pollination from the GM HT halves using a quantitative PCR assay specific to the HT (bar) gene. Rates of cross-pollination were found to decrease rapidly with increasing distance from the GM source. The quantitative data were subjected to statistical analysis and a two-step model was found to provide the best fit for the data. Significant differences were found between the results for WOSR, SOSR and varietal association (VA) crops. The model predicted that the %GM content (including upper 95% confidence limits) of a sample taken at a distance of 50 m away from the GM source would be 0.04% (0.84%) for WOSR, 0.02% (0.39%) for SOSR, 0.77% (21.72%) for WOSR VA and 0.37% (5.18%) for SOSR VA. The data and models presented here are discussed in the context of necessary separation distances to meet various possible thresholds for adventitious presence of GM in OSR.

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