Gene flow

Gene flow having occurred for millennia between wild plants and conventionally bred crops, it is reasonable to expect that it could also happen with transgenic crops. Crops vary in their tendency to outcross, and the ability of a crop to outcross depends on the presence of sexually compatible wild relatives or crops, which varies according to location.



Wheat is a self-pollinator and is unlikely to out-cross.

If as a result of outcrossing,a transgenic/wild hybrid has some competitive advantage over the wild population, it could persist in the environment and thus disrupt the ecosystem. According to the GM Science Review Panel, hybridization between transgenic crops and wild relatives seems “most likely to transfer genes that are advantageous in agricultural environments, but will not prosper in the wild … Furthermore, no hybrid between any crop and any wild relative has ever become invasive in the wild in the UK” (GM Science Review Panel, 2003: 19).

Weediness refers to the situation in which a cultivated plant or its hybrid becomes established as a weed in other fields or as an invasive species in other habitats. However there is only a very low risk of domesticated crops becoming weeds themselves because the traits that make them desirable as crops often make them less fit to survive and reproduce in the wild (ICSU, GM Science Review Panel). Weeds that hybridize with herbicide-resistant crops have the potential to acquire the herbicide-tolerant trait, although this would only provide an advantage in the presence of the herbicide (ICSU, GM Science Review Panel). According to the GM Science Review Panel, “Detailed field experiments on several GM crops in a range of environments have demonstrated that the transgenic traits investigated - herbicide tolerance and insect resistance - do not significantly increase the fitness of the plants in semi-natural habitats” (GM Science Review Panel, 2003:19). Some transgenic traits, such as pest or disease resistance, could provide a fitness advantage but there is little evidence so far that this happens or has any negative environmental consequences.More evidence is required regarding the effect of fitness-enhancing traits on invasiveness (GM Science Review Panel).

Methods are being developed to minimize the possibility of gene flow. The complete isolation of crops grown on a commercial scale, either GM or non-GM, is not currently practical although gene flow can be minimized, as it currently is between oilseed rape varieties grown for food, feed or industrial oils (GM Science Review Panel).

Management strategies such as avoiding to plant transgenic crops where their wild relatives are present, or using buffer zones to isolate transgenic varieties from conventional varieties are being considered.

Genetic engineering can be used to alter flowering periods to prevent cross-pollination or to ensure that the transgenes are not incorporated in pollen and developing sterile transgenic varieties (ICSU and Nuffield Council).Also,GM crops that produce medical or industrial substances should be designed and grown in ways that would avoid gene flow to food and feed crops (GM Science Review Panel).