杏吧原创

MORE than 20 years ago, ecologists and even genetic engineers began to express concerns that genes from engineered crops could 鈥渆scape鈥� into populations of wild relatives, possibly with damaging consequences for the environment. Since then, dozens of research projects have attempted to discover whether there are natural barriers to prevent genes in conventionally bred crops from spreading to wild plants through cross-pollination.

There is now abundant evidence that natural hybridisation occurs readily when certain crops grow close to their wild relatives: rice and wild rice, sugar beet and sea beet, for example. Hybridisation is much more limited across other species pairs, such as potato and black nightshade. But somewhere in their range of cultivation, most crops naturally cross to some extent with a wild relative.

Once this became known, researchers shifted their attention to discovering whether crop genes could persist and spread in wild populations. If crop-wild hybrids had turned out to be as sterile as mules, then transgenes could have been easily contained, but crop genes often persist in the wild beyond the initial hybrid generation. Most of the data comes from non-transgenic plants, but there is no reason to believe that transgenic crops should behave any differently.

In fact, the first known case of unintended, natural hybridisation between a transgenic crop (oilseed rape) and a wild species (wild mustard) was one of dozens of presentations on the topic of crop-to-wild gene flow at a meeting in Amsterdam last year. That meeting, entitled 鈥淚ntrogression from genetically modified plants into wild relatives鈥�, spawned this book of the same title.

The bottom line is that we should expect some transgenes to enter and persist in the populations of wild relatives of engineered crops. This book presents the details for specific crops. Questions about the relevance of such findings, however, remain largely unanswered.

When the initial concerns about transgene escape were voiced in the mid-1980s, the focus was on the possibility that a 鈥渟uperweed鈥� could evolve. Again, we can examine the precedent set by conventional crops and their wild counterparts. Most hybridisations seem to have been of taxonomic significance and little else. Exceptions are notable. A spectacular example is the appearance of a new weed beet, a natural hybrid of sugar beet and wild sea beet, causing over a billion dollars鈥� worth of damage to Europe鈥檚 sugar industry by stopping harvestable roots forming on sugar beet.

Are wandering transgenes going to create problems of their own? The concluding chapters of this book predict the impacts of transgenes in the wild and suggest how to monitor those impacts. In many ways, however, the crystal ball is as dark as it was 20 years ago. For the moment, only two transgenic traits 鈥� insect resistance and herbicide tolerance 鈥� and four transgenic crops 鈥� maize, soybean, canola and cotton 鈥� make up over 90 per cent of the transgenic acreage. And these crops are largely grown far away from their wild relatives. Over the next 10 years, as more transgenic species with new traits are approved, the opportunities for transgenes to escape into the wild may increase.