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A Framework for assessing the risk of transgenic crops. (Forum).

Article Excerpt
The environmental risks of many transgenic crops can be evaluated without additional experimentation by using already available information on the biology of the crop, the presence of compatible relatives, and the transgene phenotype. The level of crop invasiveness and the location of compatible relatives can be determined by consulting local floras and the crop literature. Decisions about invasiveness can be bolstered by determining the number of weediness traits carried by the crop and its congeners. The potential impact of transgenes can be ranked by their likely effect on reproductive success, ranging from neutral to advantageous to detrimental. This scheme can identify not only the low-risk transgene--crop combinations that are safe to deploy but also those that either are too dangerous to release or require additional experimentation.

Keywords: genetically modified crops (GMOs), genetic engineering, invasiveness, gene flow, introgression

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There is considerable international concern about the release of transgenic crops. These concerns have stalled research, particularly in Europe, where the further development of genetically modified crops has been essentially stopped. At the forefront have been fears about the risk of transgene escape into natural populations and an alteration of the "natural balance" (Colwell et al. 1985, Ellstrand 1988, Rissler and Mellon 1996, Marvier 2001). These risks are very real, and in many instances knowledge is insufficient to allow deployment of transgenic crops; however, there are cases where environmental risk can be assigned on the basis of existing knowledge about the biology of the crop, the proximity of wild relatives, and the phenotypic effects of the transgene.

Further delays of many biotechnological advances might be minimized if there were a consistent protocol that could be used to rank transgenic crops according to their environmental risk. Lengthy delays in release could be avoided by deciding at the onset of research and development what types of environmental research are needed for future deployment. In some cases, previous knowledge can be used to decide that a transgenic crop is of very low risk, and development and subsequent deployment can proceed rapidly with little additional environmental research. In other cases, transgenic crops might be deemed of such high risk that their development is foolhardy and should not progress at all. In many other cases, the transgenic crop might be considered intermediate in risk and would require varying levels of environmental research before release. Such early analyses could save considerable time at the point of release by identifying what environmental research should be done during the developmental stage. In thi s way, when the transgenic crop is ready for commercialization, it can indeed be released.

This article presents a decisionmaking framework based on answers to three questions about risk factors: (1)Is a compatible relative present in the areas of deployment? (2) Is the native relative or crop highly invasive? (3) Will the engineered trait significantly affect the invasiveness of the crop or native relative? There are other risks involved with the release of transgenic crops, such as nontarget effects of novel toxins or development of resistance in native populations, but the emphasis here will be placed on fitness effects and the potential to increase invasiveness.

The outlined framework is based on the assumption that the potential invasiveness of a plant species can be predicted if we have knowledge about its biology, its distribution, and the likely fitness impact of a transgene. The factors limiting gene flow between compatible relatives can be largely ignored, as transgenes will eventually escape into the natural environment if there is a compatible relative near the transgenic crop (Hancock et at. 1996, Ellstrand 2001), unless the transgenic crop produces no viable gametes or has a system incorporated that prevents embryo viability. With acceptance of this reality, decisions on risk can focus on evaluating the invasive characteristics of potential recipient species and determining whether the transgene itself will have a significant impact on the fitness of those species. North American crops will be used as examples, but the protocol may work in any part of the world, depending on the array of crops and the native progenitors present.

Previous research on risk of gene escape and crop invasiveness

Numerous authors have pointed out that transgene flow from engineered crops to their wild relatives could result in the evolution of increased invasiveness in wild relatives and in the evolution of pests that are resistant to newly developed control strategies (Dale 1992, Rissler and Mellon 1996, Snow and Palma 1997, Hails 2000). Invasive species are defined here as those that readily increase in numbers and aggressively spread, outcompeting other species for resources. This applies in both agronomic and native environments. A species is considered to have "increased invasiveness" if its abundance noticeably increases and it outcompetes a species that it theretofore could not.

The likelihood of hybridization between crops and their wild relatives has been measured in numerous studies (Ellstrand 2001). Although the early consensus was that such hybridizations occurred infrequently, research in the last decade has shown that they are relatively common (Ellstrand et al. 1999, Desplanque et al. 2002) and that crop alleles can persist for long periods in natural populations (Klinger and Ellstrand 1994, Arriola and Ellstrand 1996, Linder et at. 1998). Factors such as breeding system, flowering time, hybrid viability, and isolation distance can alter the rate of gene escape (Hokanson et at. 1997, Hancock et al. 1996), but if compatible relatives are within the cloud of crop pollen, genes will escape.

The first determination that should be made concerning the risk of transgene escape is whether compatible relatives exist in the area of deployment. The literature on breeding contains much information on what wild species are compatible with crops--breeders frequently want to find potential gene sources outside the immediate crop species--and considerable work has been done on elucidating the wild progenitors of crops. Several large compilations of crop histories provide portals to the literature (see Sauer [1993], Zohary and Hopf [1993], Smartt and Simmonds [1995], Hancock [2003]).

Local floras can be used to provide information...

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