Genetically Modified crops
The analogy between genetically modified crops and plant 'exotics'
6.13 Political decisions to regulate GM plants were taken largely on the basis of experience with 'alien' or 'exotic' organisms. In most countries there are many thousands of plants and some animals which are not native, but have been introduced either deliberately or accidentally. Our gardens and parks are full of plants that have been introduced, over a period of about five hundred years, from all over the world. The Victorian plant hunters were particularly active. Exotics have flourished in the new environment and are to be found in every garden centre. A few flourish to the extent that they become pests, to the detriment of native species and, possibly, to economic activity. The mussels that clog up Canada's lakes, rabbits in Australia and the grey squirrels that have nearly pushed out the UK's native red squirrels are well-known examples. Plants get less attention, but rhododendrons, Japanese knot-weed and giant hogweed are all considered serious pests in some UK environments.
6.14 So just how exotic are GM plants? Clearly the answer must depend on the nature of the new genes. Although all are exotic in the sense that the particular genetic combination achieved will not have been released into the environment before, few are likely to cause problems, just as few exotic introductions cause problems. Critics of the analogy with exotic organisms argue that conventional introductions that cause problems are more likely to be radically different from anything present in that environment before. In the case of GM plants, a familiar crop with a few, often very few, genetic changes is involved.
6.15 It is not generally realised that crop plants are usually uncompetitive outside their normal agricultural environments, since they have been bred for characteristics that humans want, at the expense of traits that enable them to flourish in wild conditions. One such crop is wheat. However, if the genes inserted were to increase the plant's competitive ability in any way, there may be potential to disrupt natural eco-systems. The finding from the GM plants studied to date is, on the one hand, that introduction of the foreign gene does not increase the plants competitiveness in the wild, and if there is no selection pressure for maintenance of the transgene, then the transgene itself may be lost in a few generations.(3) On the other hand, a recent research report suggests that GM insect-resistant rapeseed survives better in a wild environment than non-GM oilseed rape, so caution is required and further research is vital.(4)
6.16 Accordingly, it is the traits that increase competitive behaviour that are of primary concern. These traits involve genes that increase general vigour and growth, genes which increase a crop's ability to survive outside the normal agricultural environment or genes which affect 'fitness' in any way. A plant's ability to spread its genes to near relatives is also a concern, in case the near relatives take on competitive characteristics. Some crop plants are effectively 'biologically isolated'. They have no near relatives with which they can interbreed and there is therefore no risk of genetic transfer. For example, maize and potatoes have been developed from plants endemic to South America and have no European relatives with which they can hybridise.5
6.17 Oilseed rape and sugar beet, however, have been developed from European native plants and both have been shown to be capable of transferring genes to related wild species.(6) Thus, the risk of 'transgene escape' is related to the environment in which the crops are being grown. GM potatoes in South America would raise more concerns about genetic transfer than would the same crops in Europe.(7) We consider that the analogy with exotics has been a helpful one in regulating the release of GM crops.
6.18 Research is currently being carried out into ways to limit interspecies hybridisation. The pollen dispersal and gene flow of transgenic crops has been studied(8) and is being compared to data about similar, non-transgenic crops.(9) This allows assessments to be made about the distances GM crops must be planted from wild relatives and other plants to reduce risks of hybridisation. Research is also being carried out into ways to prevent pollen-mediated transmission of transgenes by ensuring that transgenic DNA (deoxyribonucleic acid) is not incorporated into pollen (see paragraph 2.29).(10)
What benefits and risks do GM crops bring to the environment?
6.19 A considerable amount has been said and written already about both the potential benefits and risks to the environment of GM plants, but we are only beginning to accumulate the data that will enable us to evaluate precisely the pros and cons of these issues, or more correctly, series of issues. This is an argument for continued, controlled research. If further research indicates that some particular applications of GM technology pose such risks to the environment that they should not go into commercial production, they should be withdrawn. The most difficult aspect of the discussion of risks and benefits is whether to develop a mechanism for weighing them up against each other. This is not an explicit part of our current policy and regulatory approaches. The arguments for and against doing so are explored further in Chapter 7.
Footnotes3 See, for example, Brookes M (1998) Running Wild, New Scientist, No. 2158:38-41 and the discussion reported in Masood E (1999) UK gets the green light on modified crops, Nature, 397: 286.
4 Stewart C, All J, Raymer P and Ramachandran S (1997) Increased fitness of transgenic insecticidal rapeseed under insect selection pressure, Molecular Ecology, 6: 773-779.
5 Raybould A and Gray A (1993) Genetically modified crops and hybridisation with wild relatives: a UK perspective, Journal of Applied Ecology, 30: 199-219.
6 Mikkelsen T, Andersen B and Jorgensen R (1996) The risk of crop transgene spread Nature, 380:31; Timmons A, O'Brien E, Charters Y, Dubbels S and Wilkinson M (1995) Assessing the risks of wind pollination from fields of genetically modified Brassica napus ssp. olifera, Euphytica, 85:417-23.
7 Brookes M, Running Wild, p. 38-41.
8 For example Scheffler J (1993) Frequency and distance of pollen dispersal from transgenic oilseed rape (Brassica napus), Transgenic Research, 2:356-364; van Raamsdonk L and Schouten H (1997) Gene flow and establishment of transgenes in natural plant populations, Acta Botanica Neerlandica, 46:69-84.
9 Hokanson S, Hancick J and Grumet R (1997) Direct comparison of pollen-mediated movement of native and engineered genes, Euphytica, 96:397-403.
10 Daniell H, Datta R, Varma S, Gray S and Lee S (1998) Containment of herbicide resistance through genetic engineering of the chloroplast genome, Nature Biotechnology, 16:345-348; Gray A and Raybould A (1998) Reducing transgene escape routes, Nature, 392: 653-654.