Gene flow

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Friday, 10 July 2009 06:05

The source document for this Digest states: Scientists agree that gene flow from GM crops is possible through pollen from open-pollinated varieties crossing with local crops or wild relatives. Because gene flow has happened for millennia between land races 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 (Box 23 on page 70) (ICSU, GM Science Review Panel). Scientists do not fully agree whether or not gene flow between transgenic crops and wild relatives matters, in and of itself (ICSU, GM Science Review Panel). If a resulting transgenic/wildhybrid had some competitive advantage over the wild population it could persist in the environment and potentially disrupt the ecosystem. According to the GM Science Review Panel, hybridization between transgenic crops and wild relatives seems “overwhelmingly 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). Whether the otherwise benign flow of transgenes into land races or other conventional varieties would itself constitute an environmental problem is a matter of debate, because conventional crops have long interacted with land races in this way (ICSU). Research is needed to improve the assessment of the environmental consequences of gene flow, particularly in the long run, and to understand better the gene flow between the major food crops and land races in centres of diversity (ICSU, GM Science Review Panel). 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. Scientists agree that 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 (ICSU, GM Science Review Panel). More evidence is required regarding the effect of fitness-enhancing traits on invasiveness (GM Science Review Panel). Management and genetic 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 include avoiding the planting of transgenic crops in their centres of biodiversity or where wild relatives are present, or using buffer zones to isolate transgenic varieties from conventional or organic varieties. 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). The GM Science Review Panel and other expert bodies recommend that 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).

Last Updated on Friday, 10 July 2009 08:41