Gene flow has and will continue to occur between sexually compatible plant species in agricultural habitats. What are the implications for growing genetically modified crops?

1. Cross-pollination occurs between sexually compatible species /crops ^{1,2, 3}

2. Likelihood of cross-pollination is determined by the proximity of sexually compatible crops/plant species and where there is synchronous flowering. ⁴

3. Distance viable pollen can travel ⁶is influenced by the dispersal mechanism and pollen longevity - both of which are species dependent^7,8

4. Pollination falls off rapidly with distance but that the distance at which pollination is zero is impossible to determine with accuracy ⁹

5. Consequences of transfer of novel genes from GM crops to weeds depend not only on physical distribution but on the nature of the gene and the biology and ecology of the recipient¹⁰

-Herbicide tolerance unlikely to confer and advantage outside agricultural areas ¹¹
-Insect resistance may confer advantage under certain conditions ^{12, 13}

6. Many plant species can be found both as a crop and a weed¹⁴. Change in habitat may potentially result in the evolution of a weed from a cultivated plant or from a feral that is closely related to a cultivated species ^{15,16,17, 18}

7. Chloroplast transformation may reduce likelihood of gene transfer by pollen¹⁹. However, the potential for horizontal gene transfer may increase ²⁰

8. Herbicide tolerance (HT) can develop by evolution and selection within weed populations continually sprayed with the same herbicide rather than by gene flow from a herbicide tolerant crop ^21,22

9. GM herbicide tolerant plants are no more likely to be invasive in agricultural fields or natural habitats than non-GM counterparts.²³

References

1. Garcia M, Fugueroa CJ, Gomez L, Townsend R and Schoper J 1998 Pollen control during transgenic hybrid maize development in Mexico Crop Science 38 1597-1602

2. AriasDM and Rieseberg LH 1994 Gnee flow between cultivated and wild sunflowers TAG 89 655-660

3. Snow AA, Andersen B and Jorgensen RB 1999 Costs of transgenic herbicide resistance introgressed from Brassica napus into weedy B.rapa Molecular ecology 8 605-615

4. Ellstrand NC, Prentice HC and Hancock J 1999Gene flow and introgression from domesticated plants into their wild relatives. Ann Rev Ecol and System 30:539-563.

5. Raybould AF and Gray AJ 1993 Genetically modified crops and and hybridisation with wild relatives : a UK perspective. J App Ecol 30:199-219

6. Lutman PJ (ed) 1999 Gene flow and agriculture: relevance for transgenic crops BCPC, London

7. Squire GR, Crawford JW, Ramsay G, Thompson C and Brown J 1999 Gene flow at the landscape level. In gene flow and Agriculture: relevance for transgenic crops p57-64 9BCPC, London)

8. Cresswell JE, Osborne JL and Bell SA 2002 A model of pollinator mediated gene flow between plant populations with numerical solutions for bumblebees pollinating oilseed rape OIKOS 98 375-384

9. Moyes CL and Dales PJ 1999 Organic farming and gene transfer from genetically modified crops MAFF research report

10. Hails R, Reeds M Kohn DD and Crawley MJ 1997 Burial and seed survival in Brassica napus subspecies oleifera and Sinapis arvensis including a comparison of transgenic and non-transgenic lines of the crop Proc R. Soc London B. Biol Sci. 264 1-7

11. Crawley MJ, Brown S, Hails R Kohn DD and Rees M. 2001 Transgenic crops in natural habitats Nature 409 682-683

12. Stewart AN, All JN , Raymer PL and Ramachandran S 1997 Increased fitness of transgenic insecticidal rapeseed under insect selection pressure. Mol Ecol 6:773-779

13. Ramachandran S, Buntin D, All JN,Ramer PL and Stewart CN 2000 Intraspecific competition of an insect resistance transgenic canola in seed mixtures Agron J 92 368-374

14. Keeler KH, Turner CE and Bolick MR 1996 Movement of crop transgenes into wild plants .In Herbicide resistant crops - Agricultural, Environmental, Economic,Regulatory and Technical aspects 303-330 (Lewis Publishers London)

15. National Research Council 2000 Genetically modified pest protected plants: science and regulation ( National Academic press Washington)

16. National Research Council 1989 Field testing genetically modified organisms: framework for decision (National Academic press Washington)

17. Ammann K, Jacot Y and Al Mazyard R (2000) Weediness in the light of new transgenic crops and their potential hybrids J Plant Dis 17 19-29

18. Boudry P Morchen M Saumitou-Lapradep Verent p and Van Dijk H. (1993) The origin and evolution of weed beets : consequences for breeding and release of herbicide resistant transgenic sugar beets TAG 87 471-478

19. DaniellH, Datta, R, Varma S, Grat S and Lee SB 1998 Containment of herbicide resistance through genetic engineering of the chloroplast genome. Nature biotechnology 16: 345-348

20. Bertolla F, Nalin R and Simonet P. 2002 In Situ transfer of antibiotic resistance genes from transgenic (Transplastomic) tobacco plants to bacteria Applied and Environmental Microbiology 68, 3345-3351

21. Moyes Cl, Lilley JM, Casais Ca, Cole SG, Harger PD and dale PJ 2002 Barriers to gene flow from oilseed rape ( brassica napus) into populations of Sinapis arvensis Moleculare ecology 11 103-112

22. Senior IJ and Dale PJ 2002 Herbicide tolerant crops in agriculture: oilseed rape as a case study. Plant breeding 121 97-101.

23. Gene Flow to Wild Plant Relatives 2001 Council for Biotechnology Information www.whybiotech.com/html/pdf/Gene_Flow_to_Wild_Plant.pdf