When Transgenes Wander, Should We Worry?

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Abstract
It is hard to ignore the ongoing, often emotional, public discussion of the impacts of the products of crop biotechnology. At one extreme of the hype is self-rightoeus panic, and at the other is smug opti- mism. While the controversy plays out in the press, dozens of scientific workshops, symposia, and other meetings have been held to take a hard and thought- ful look at potential risks of transgenic crops. Over- shadowed by the loud and contentious voices, a set of straightforward, scientifically based concerns have evolved, dictating a cautious approach for creating the best choices for agriculture's future. Plant ecologists and population geneticists have looked to problems associated with traditionally im- proved crops to anticipate possible risks of trans- genic crops. Those that have been most widely dis- cussed are: (a) crop-to-wild hybridization resulting in the evolution of increased weediness in wild rela- tives, (b) evolution of pests that are resistant to new strategies for their control, and (c) the impacts on nontarget species in associated ecosystems (such as the unintentional poisoning of beneficial insects; Snow and Palma, 1997; Hails, 2000). to multiply itself repeatedly through reproduction, which can frustrate attempts at containment. In the early 1990s, the general view was that hy- bridization between crops and their wild relatives occurred infrequently, even when they were growing in close proximity. This view was supported by the belief that the discrete evolutionary pathways of do- mesticated crops and their wild relatives would lead to increased reproductive isolation and was sup- ported by challenges breeders sometimes have in obtaining crop-wild hybrids. Thus, my research group set out to measure spontaneous hybridization between wild radish (Raphanus sativus), an important California weed, and cultivated radish (the same spe- cies), an important California crop (Klinger et al., 1991). We grew the crop as if we were multiplying commercial seed and surrounded it with stands of weeds at varying distances. When the plants flow- ered, pollinators did their job. We harvested seeds from the weeds for progeny testing. We exploited an allozyme allele (Lap-6) that was present in the crop and absent in the weed to detect hybrids in the progeny of the weed. We found that every weed seed analyzed at the shortest distance (1 m) was sired by the crop and that a low level of hybridization was