Coexistence in Maize: Efficacy of non-GM border rows in reducing pollen-mediated gene flow

A non-GM maize border directly at the edge of the field grown with GM maize has been considered as coexistence measure and already found its way into national coex­istence regulations of several EU member states. In large scale field experiments we tested the efficacy of 9 m and 18 m wide recipient maize borders in combination with different isolation distances. In 2008, we combined non-GM maize borders with an isolation distance of 51 m in three sites in Germany. We could not observe any effect up to 18 m wide non-GM maize borders on pollen-mediated gene flow. In a modified field trial conducted in 20 I O to 2012 the isolation distance between donor and recipient field was reduced to 6 m and 12 m, respectively, to assess the efficacy of border rows as coexistence measure for small structured agricultural landscapes. In these trials maize gene flow was investigated using a GM-free test system based on the trait kernel color. Results obtained point out that both, 9 m and 18 m wide recipient maize borders do not reliably reduce outcrossing rates in the whole field's harvest regardless of the tested isolation distance (6, 12, 51 m).