Ecological impacts of genetically modified crops - Experiences from ten years of experimental field research and commercial cultivation

There is general scientific agreement that gene flow from GM crops to sexually compatible wild relatives can occur. Experimental studies have shown that GM crops are capable of spontaneously mating with wild relatives, however at rates in the order of what would be expected for non-transgenic crops. Few studies have shown that GM herbicide tolerant (GMHT) oilseed rape (Brassica napus) can form F1 hybrids with wild turnip (Brassica rapa) at low frequency under natural conditions. Questions remain whether these transgenes would cause ecologically relevant changes in recipient plant populations. Although there is a low probability that increased weediness due to gene flow could occur, it is unlikely that GMHT weeds would create greater agricultural problems than conventional weeds. Farmers can generally choose among several herbicides for the cultivation of a given crop and they have further a set of options within a crop rotation to control or manage weeds.
In natural habitats, no long-term introgression of transgenes into wild plant populations leading to the extinction of any wild plant taxa has been observed to date. Transgenes conferring herbicide tolerance are unlikely to confer a benefit in natural habitats because these genes are selectively neutral in natural environments, whereas insect resistance genes could increase fitness if pests contribute to the control of natural plant populations.