Gene flow from crops to wild plants and its population-ecological consequences in the context of GM-crop biosafety, including some recent experiences from lettuce


  • C. Van de Wiel
  • M. Groot
  • H. Den Nijs


The public concern about the impact of genetically modified crops on the natural environment triggered a steady stream of research during the last decade. Among the possible impacts, the ‘escape’ of the transgene, either through dispersal of the crop plant outside the agricultural area or through hybridization with wild relatives, attracted a lot of attention, in particular in relation to the possibility of increasing ‘weediness’. For gene flow through hybridization to occur, pollen grains must achieve fertilization and seeds must germinate and produce sexually mature plants. Subsequently, the first generation hybrids should be sufficiently fit to survive to sexual maturity and thus produce follow-up generations by which actual introgression into wild acceptor-species genomes could occur through repeated backcrossing. All these steps are reviewed in this paper. It will become evident that, in order to estimate a transgene’s capacity to introgress and persist in wild relatives, all steps in the introgression process should be considered. Areas where still relatively little definite data has been published are i) assessing the extent to which genes, such as those conferring resistance to biotic as well as abiotic stresses, indeed enhance fitness in natural settings and the consequences of introgression of these for these environments; and ii) improving this assessment of fitness, e.g. by not only scoring relevant traits, such as those related to fecundity, but also monitoring them in realistic field situations. In this regard, more data on, for instance, the effects of the transgene insertion site on the introgression process and the importance of fitness of the intermediate stages (backcrosses) would be needed to reach a more general insight. In relation to co-existence of GMO and organic agriculture, crop-to-crop gene flow also needs to be controlled. Therefore, a wide variety of possible hybridization barriers, both physical and biological, are discussed. The technical limitations of assessing introgression from crop to wild avoiding the use of transgenic markers are discussed on the basis of work on lettuce