Jun 21, 2011

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Gene flow in wheat: Model calculations

Outcrossing of GM wheat under selection pressure

Crop	Barley /wheat
Year	2006
Country	Canada
Execution	Department of Plant Sciences, University of Manitoba, Kanada

Experiment

Type:

Model calculations on the dispersal behaviour of herbicide-tolerant GM wheat

Calculation model:

Mathematical models were used to predict how extensively and how quickly herbicide-tolerant GM wheat can spread to neighbouring conventional wheat fields and become established as volunteer wheat in conventional follow-on crops. The authors assumed that the fields in question are regularly treated with the herbicide for which the wheat plants possess a genetically engineered tolerance. This confers a high selective advantage on the GM wheat plants compared with wheat plants that do not possess the herbicide tolerance trait. The application of the same herbicide on fields with GM wheat and fields with conventional wheat plants represents a hypothetical situation. These days, different herbicides would usually be applied. However, if herbicides drift during spraying, strips and edges of conventional fields can come into contact with the herbicide sprayed on the GM wheat field and GM wheat could accumulate there as a result.

Results

According to the literature, the outcrossing rate from wheat plants to neighbouring conventional crops is between 0.2 and 3.8 per cent within a radius of ten metres, depending on the variety. For fields larger than ten hectares, the average outcrossing rate for the entire harvest is less than 0.1 per cent.

If the GM wheat is herbicide-tolerant and the corresponding herbicide regularly ends up in conventional wheat fields, e.g. along the field edges, GM plants can accumulate there. According to the calculations, herbicide-tolerant wheat can make up 50 per cent of the volunteer wheat after just two to six generations. Herbicide-tolerant volunteer wheat must therefore, according to the authors, be controlled by means of systematic crop rotation measures and by switching herbicides.

Even without selection pressure through the use of herbicides, GM wheat can accumulate on conventional fields if the farmer uses part of his conventional harvest as seed for the next season (replanting). In this case, the ratio of GM wheat in the conventional field, assuming an average outcrossing rate of 0.1 per cent, would increase to 0.9 per cent after approx. 15 growing seasons.

Documentation