<em>Ex Ante</em> evaluation of gene flow in oilseed rape with cropping system models

Chapitre 4International audienceOilseed rape (OSR) genes can escape fields in space via pollen and seeds, and in time via volunteers resulting from seeds lost before or during oilseed rape harvest. When varieties co-exist, e.g. genetically-modified (GM) and non-GM varieties, this spatio-temporal gene flow can lead to the adventitious presence of GM seeds in non-GM harvests and thus cause financial losses for farmers and cooperatives. Gene flow depends on crop locations, succession, and management, as well as the location and management of semi-natural areas such as roadverges. The objective of this investigation was to present a simulation methodology using the spatially-explicit cropping system model GENESYS for proposing and evaluating prospective cropping systems.The simulation study evaluated pre-sowing OSR seed lot impurity, characteristics of OSR varieties, local management measures (buffer zones, harvest discarding), cropping system components (crop succession, tillage options, sowing datesetc) and landscape characteristics (field sizes and shapes, crop locationetc). These simulations can be used to determine regional co-existence measures such as isolation distances or crop proportion as a function of cropping system type, the accepted risk of field or batch loss, and the harvest impurity thresholds used by the decision-makers