The first study on cross-fertilization between Bt and conventional maize in real situations of co-existence in two regions of Spain has been published in the Plant Biotechnology Journal. The authors recommend the establishment of isolation distances of 20 metres and the planting of varieties with different flowering times.
The research work, which was presented already at the European conference on co-existence in Vienna in spring, shows similar findings to previous field trials and simulations. The least surprising result was the rapid decrease of cross-fertilisation in the conventional field in the direction of its centre. The actual frequency of out-crossing was determined largely by two factors: the temporal distance between the flowering times of the GM and the conventional maize varieties, and the isolation distances between the fields of both agricultural systems.
In contrast to the draft of the upcoming Spanish law on co-existence, which requires isolation distances of 220 metres, the study considers distances of 20 metres sufficient to ensure that the GM share in the harvest of the total conventional field remain below the labelling threshold of 0.9 percent. If the conventional and the GM maize varieties flower at different times, even smaller isolation distances may be used.
Evaluating a real situation in which several GM and conventional fields interact with each other, this co-existence study was the first to be conducted under real conditions.