In this experiment at CIMMYT, the international corn and wheat research center, genetically engineered herbicide resistance failed. Note the dead zone where herbicide was painted on the leaf. Photos © David Tenenbaum
Is it smart to teach plants to resist herbicides?
While insect resistance could reduce the amount of chemicals used on crops, herbicide resistance could increase it. Nonetheless, several seed companies have already made transgenic crops with immunity to herbicides that would normally kill them. This allows farmers to spray the field with herbicides after the crop emerges from the ground, zapping the weeds.
On the face of it, the idea seems unlikely to be adopted on environmental grounds. Yet if the chosen herbicide is less toxic than the one presently used, it could have benefits. And certainly, Roundup, generically called glyphosate, the herbicide to which Monsanto has conferred resistance in soybeans and other crops, is less toxic than most herbicides. Glyphosate stays where it's put in the field and breaks down quickly.
But problems can arise. In 1997, thousands of acres of supposedly Roundup-resistant cotton were killed in Mississippi by the herbicide. Monsanto says it has reached settlements with two dozen farmers (see "Cotton Growers Say Strain Cuts Yields" in the bibliography). "We concluded it was a combination of unusual weather patterns and generous use of Roundup," says public relations director Karen Marshall. "We'll give better directions next time."
Furthermore, glyphosate drift could affect plants outside fields. And the advent of Roundup-resistant poplar trees has raised the specter of vast tracts of diverse northern forests being converted to huge monocultures.
Ruining the relatives
|Suketoshi Taba, a breeder CIMMYT in Mexico, examines a new hybrid corn made with conventional breeding. If they crossbreed with crop relatives, hybrid and transgenic corn could harm essential sources of new genes.||Perhaps more important is the related question of whether the new genes could pollute a crop's relatives. Should transgenic corn be grown in the regions of Mexico where corn originated, where wild relatives and old corn varieties both provide genes for insect or disease resistance to new varieties of corn?|
That idea gives corn breeders the shivers, since it could harm the source of genetic diversity that underlies all conventional plant breeding. And yet Monsanto's Karen Marshall says it could be done, with an adequate plan for preventing gene transfer. "It's a management problem. We would still sell the seeds there."
Yet as more genes are transferred across more species lines, without any requirement for warning labels, such problems could become more common. An estimated two percent of adults and eight percent of children have food allergies, which can be deadly.
Taking the long view
"When you go to release organisms into the environment, you're never 100 percent sure what's going to happen," says David Pimentel, who studies the environmental impact of agriculture and other resource-consuming activities at Cornell University (see "Genetic Engineering in Agriculture and the Environment" in the bibliography). He notes that at least 128 crop plants have started acting like weeds, proving that the law of unintended consequences is alive in agriculture.
Genetic engineering, he says, "is not inherently good or bad. I think you have to be cautious. We get more than 99 percent of our food from the land."
Want to surf our transgenic resources?
There are 1 2 3 4 5 6 pages in this document.
Bibliography | Credits | Search