Modeling the influence of gene flow and selection pressure on the frequency of a GE herbicide-tolerant trait in non-GE wheat and wheat volunteers

Different types of transgenic wheat (Triticum aestivum L.) will be ready for commercialization within the next decade, including varieties with higher yields, greater tolerance to biotic and abiotic stresses, and resistance to herbicides. The release of genetically engineered (GE) wheat may require segregation of GE and non-GE wheat to satisfy international markets. Before GE wheat is released, it is important to understand the movement of a GE trait within the agronomic production system. This study evaluated the effects of gene flow and selection pressure on the frequency of a GE trait (herbicide tolerance) in non-GE wheat and wheat volunteers. Gene flow of GE traits to non-GE wheat is inevitable through pollen or seed movement. When a GE trait does not confer a selective advantage in the production system, the frequency of the GE trait within non-GE wheat will be a function of the rate of gene flow. Low rates of gene flow will lead to low levels of the GE trait in the non-GE crop. With repeated gene flow events, the frequency of the GE trait may slowly increase in the non-GE crop. When the GE trait has a selective advantage, the frequency of the GE trait will increase rapidly in volunteer populations of the non-GE crop. Herbicide tolerance is an example of a GE trait that provides a high selective advantage when the herbicide is applied in the production system. Predictive models show that even with very low rates of initial gene flow, frequent applications of a highly effective herbicide will quickly increase the frequency of the herbicide-tolerant (HT) GE trait in volunteer populations. This has negative implications for control of volunteers and the ability to maintain tolerance levels of GE traits in non-GE wheat crops.