Definition and feasibility of isolation distances for transgenic maize cultivation

Abstract

A major concern related to the adoption of genetically modified (GM) crops in agricultural systems is the possibility of unwanted GM inputs into non-GM crop production systems. Given the increasing commercial cultivation of GM crops in the European Union (EU), there is an urgent need to define measures to prevent mixing of GM with non-GM products during crop production. Cross-fertilization is one of the various mechanisms that could lead to GM-inputs into non-GM crop systems. Isolation distances between GM and non-GM fields are widely accepted to be an effective measure to reduce these inputs. However, the question of adequate isolation distances between GM and non-GM maize is still subject of controversy both amongst scientists and regulators. As several European countries have proposed largely differing isolation distances for maize ranging from 25 to 800 m, there is a need for scientific criteria when using cross-fertilization data of maize to define isolation distances between GM and non-GM maize. We have reviewed existing cross-fertilization studies in maize, established relevant criteria for the evaluation of these studies and applied these criteria to define science-based isolation distances. To keep GM-inputs in the final product well below the 0.9% threshold defined by the EU, isolation distances of 20 m for silage and 50 m for grain maize, respectively, are proposed. An evaluation using statistical data on maize acreage and an aerial photographs assessment of a typical agricultural landscape by means of Geographic Information Systems (GIS) showed that spatial resources would allow applying the defined isolation distances for the cultivation of GM maize in the majority of the cases under actual Swiss agricultural conditions. The here developed approach, using defined criteria to consider the agricultural context of maize cultivation, may be of assistance for the analysis of cross-fertilization data in other countries.

Cross-fertilization between genetically modified and non-genetically modified maize crops in Uruguay

“…Studies on gene-flow by cross-fertilization were reviewed by Devos et al (2005) and Sanvido et al (2008). Many of them aimed to provide information to define the necessary isolation distances, so that the presence of transgenes in non-GM crops could be maintained below certain threshold levels.…”

Coexistence in the EU—return of the moratorium on GM crops?

“…In ex ante coexistence regulations, preventive on-farm measures are prescribed volume 26 number 11 november 2008 nature biotechnology the cropped area 5,10,11 . In these cases, it is highly probable that isolation perimeters would interfere with adjacent non-GM maize fields.…”

“…Because such situations might not often arise in practice, fixed isolation distances can be unnecessarily conservative. In real agricultural conditions, fields are planted with GM and non-GM maize varieties with different sowing or flowering dates, and agricultural landscapes comprise a mix of maize fields, other crops and physical and/or natural barriers 5,8,10 .…”

“…A key issue is that if non-GM crop products were admixed with GM crop products at levels above the EU tolerance threshold, such distance from the pollen source, spatially isolating GM maize from non-GM maize is an efficient measure to reduce the extent of cross-fertilization 4,5 . However, imposing wide and fixed isolation distances around GM maize fields entails four challenges to EU policymakers.…”

“…A challenge that faces member states is how to define appropriate and thus scientifically defensible isolation distances. Crossfertilization studies mimicking worst-case on-farm situations demonstrated that in many cases isolation distances exceeding 50 m are not necessary to comply with the tolerance threshold of 0.9% in grain maize [4][5][6][7] . Similar conclusions have been drawn from cross-fertilization studies performed under real agricultural situations in Spain 8 and from predictive vertical gene flow modeling at the landscape level in France 9 .…”