Assessing the value of imperfect biocontainment nationally: rapeseed in theUnitedKingdom as an exemplar

Summary Paternal biocontainment methods ( PBM s) act by preventing pollen‐mediated transgene flow. They are compromised by transgene escape via the crop‐maternal line. We therefore assess the efficacy of PBM s for transgenic rapeseed ( B rassica napus ) biocontainment across the U nited K ingdom by estimating crop‐maternal hybridization with its two progenitor species. We used remote sensing, field surveys, agricultural statistics, and meta‐analysis to determine the extent of sympatry between the crop and populations of riparian and weedy B . rapa and B . oleracea . We then estimated the incidence of crop‐maternal hybridization across all settings to predict the efficacy of PBM s. Evidence of crop chloroplast capture by the progenitors was expanded to a national scale, revealing that crop‐maternal gene flow occurs at widely variable rates and is dependent on both the recipient and setting. We use these data to explore the value that this kind of biocontainment can bring to genetic modification ( GM ) risk management in terms of reducing the impact that hybrids have on the environment rather than preventing or reducing hybrid abundance per se .