Rissler and Mellon's book focuses on two main categories of environmental risk: (1) the potential for certain transgenes to confer or enhance weediness in some crops (either by enabling the crop to persist in the field or by increasing its ability to invade new habitats) and, (2) the movement of transgenes via pollen from engineered crops into populations of nearby wild relatives. In either case, if the transgenes are for traits that may confer higher fitness, such as resistance to herbicides, disease, or insects, then it is possible for the transgenic crop/wild relative to gain a selective advantage and thereby result in a "better" weed that is more difficult to control. In addition to exacerbating weed problems on a farm, transgenic wild weedy plants potentially could invade natural communities causing local extinction of native populations and thereby alter community composition. The authors rightly point out that of particular concern are transgenic crops that already have weedy tendencies or that have cross-compatible wild relatives that are weeds. The authors also briefly discuss the potential environmental risks of virus-resistant plants and suggest that the widespread use of transgenic crops could adversely impact centers of crop diversity and thereby diminish the genes available for breeding new characteristics into crops.
Rissler and Mellon recommend a number of steps to address these concerns and propose a workable three-tiered scheme to (1) evaluate whether a transgenic crop will become a weed and, (2) to evaluate the potential for transgene flow via pollen from an engineered crop to a wild relative and subsequently, to assess the wild relative for increased weediness. Moreover, the authors indicate that the United States government should strengthen its regulatory programs regarding the commercial release of transgenic crops.
Although parts are a bit repetitive, this book is well written and informative and the generally nontechnical prose make it accessible to a wide audience. In the classroom, it (along with a second text) would make for an interesting discussion-oriented course on the pros and cons of agricultural biotechnology. For plant ecologists and evolutionary biologists reading this book, potential fitness-enhancing properties of certain transgenes (and their possible environmental consequences) may spark interesting lines of applied research. Perhaps, most importantly, this book should stimulate debate among environmental regulators, policy makers, agricultural biotechnologists and the general public, on the future role of engineered crops. If you are interested in environmental issues related to recombinant DNA technology, I would recommend this book -Timothy P. Spira, Department of Biological Sciences, Clemson University