The farm scale evaluations of gene flow from GM to other crops carried out in Britain during the past few years have once more confirmed for fodder maize that coexistence between GM and non-GM cultivation presents few problems in preventing significant GM gene content in possible recipients.

One particular study was carried out by the Central Science Laboratory in York and the Centre for Ecology and Hydrology at Winfrith, U.K. using crop-to-crop gene flow based on the farm scale study sites of fodder maize. The objective was to explore the extent of pollen-mediated gene flow and to assess whether or not the distances recommended by the Supply Chain Initiative on Modified Agricultural Crops (the body set up to advise farmers on GM agriculture) for separating GM- and non-GM-maize were adequate.

Using Liberty LinkTM Line T25 maize (containing the pat gene, tolerant to the herbicide glufosinate), more than 1,000 samples were collected from over 50 split-field sites during a three-year period: half of each field was sown with the Liberty-Link line versus half with an equivalent conventional maize.

Gene flow was detected over a range of 200 metres, decreasing rapidly with increasing distance from the GM-maize source. Separation distances were found not to correlate closely with field size so, for example, that a 25-fold increase in area reduced the separation distance only by 8 metres for a 0.1% GM content threshold; note, however, that 0.1%, while an aspiration of certain lobby groups, has no legal standing. The current EU legal standard of 0.9% GM content above which a product must be labelled would require a separation distance of only 3 metres for a field 150 metres in length. To be below a 0.1% threshold, that 150 metre field would require a separation distance of 79 metres. It is clear from these results that a threshold of 0.9% is achievable in practical terms while one of 0.1%, quite unnecessary except for doctrinaire reasons, would not.

The extent of gene flow from a GM source into an non-GM recipient (and vice versa) will depend not only on distance but on the relative local areas of the two types of crop. One type in a small field surrounded by many fields of the other will clearly be more likely to show inward gene flow than a small area source impinging on a large area of recipient plants.

The authors do conclude that, with effective modelling, it is possible to meet current EU thresholds for bulk crops.

Source:

Weekes R, Allnutt T, Boffey C, Morgan S, Bilton M, Daniels R, Henry C. (2007) A study of crop-to-crop gene flow using farm scale sites of fodder maize (Zea mays L.) in the UK. Transgenic Research, vol. 16, pages 203-211

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