Sowing and flowering delays can be an efficient strategy to improve coexistence of genetically modified and conventional Maize
The coexistence between genetically modified (GM) and non-GM maize (Zea mays L.) fields is subjected to regulation in several countries. A strategy to reduce cross-pollination from GM to non-GM fields was evaluated, on the basis of reducing the flowering coincidence by sowing at separate times. The trial included narrow plots in which transgenic maize was sown before, simultaneously, and after adjacent non-GM maize. A three-week delay between GM and non-GM sowing dates resulted in flowering delays below 5 d for early sowings, but up to 10 to 15 d for late sowings. Cross-pollination was monitored by xenia effect and validated by real-time PCR. The combined effect of flowering delay and distance from the pollen source was evaluated. Cross-pollination dramatically decreased with distance between pollen source and receptor. Flowering delay interacted with distance to the pollen donor source and further reduced GM pollen flow in all cases. Thus, it acted as a regulatory factor. A flowering delay of 92.9 growing degree units (GDU) (7 d in our experimental conditions) was enough to reduce the adventitious presence of GM kernels in non-GM maize plots down to residual values. This study illustrates the possibility of improving coexistence through temporal separation of flowering dates on the basis of appropriate delays in sowing dates.