Jonathan Latham and Allison Wilson
A key aspect of transgenic agriculture is control of gene flow. Gene flow is important for many reasons including: 1) protecting intellectual property from unwanted incursions into farmers’ fields (and vice-versa); 2) maintaining the genetic integrity of crop cultivars; 3) maintaining labelling and consumer choices; and 4) biosafety risk assessments which presume limited transgene dispersion and that transgenic traits can be removed from circulation.
Coexistence between genetically modified (GM) and non-GM plants is a field of rapid development and considerable controversy. Predicting GM volunteer emergence in subsequent non-GM crops is one important aspect of this. Theoretical models suggest recruitment from the seedbank over extended periods, but empirical evidence matching these predictions has been scarce.
In a paper published in Biology Letters, D’Hertefeldt, Jørgensen and Pettersson (2008) provide evidence of long-term GM seed persistence in conventional agriculture. Ten years after a trial of GM herbicide-tolerant oilseed rape, emergent seedlings were collected and tested for herbicide tolerance. In line with volunteer reduction recommendations established at the time of the original experimental trial, the field had been ploughed every year, harrowed, and planted with wheat, barley and sugar beet. Volunteers were controlled by herbicide application and visual inspection to ensure that no transgenic volunteers would flower. Seedlings that survived the glufosinate herbicide (15 out of 38 volunteers) tested positive for at least one GM insert and most probably originated from the original trial. The resulting density was equivalent to 0.01 volunteer GM plants per square metre. These results are important in relation to debating and regulating coexistence of GM and non-GM crops.