By | November 07, 2005 | archive, textbook

The people of Oaxaca, Mexico have been cultivating corn for nearly 10,000 years. During that time, corn varieties have developed through traditional breeding methods to both enhance nutrition and provide insurance against an unpredictable environment. The success of these varieties has established corn as the centerpiece of the Mexican landscape, diet, and culture. Many of the corn varieties we use today can be traced back to this region. In recent decades, recombinant DNA technologies have facilitated a radical transformation of the way corn is bred and cultivated. These changes may lead to a profound impact on the way of life in Oaxaca.

Biotechnologists can use numerous methods to insert designer genes from a variety of organisms into plant genomes. A transgenic or genetically modified (GM) plant produced this way may have genes added to improve flavour or nutrition, but most transgenes are designed to improve resistance to insects or herbicides.

Arguably, genetically modified crops provide farmers and consumer with definite benefits due to reduced crop losses from pests and weed competition. For the people of Oaxaca, such benefits are overshadowed by the potential risks of these transgenic crops to the traditional corn varieties that have been bred to suit the region. While transgenes may be stable within a GM plant’s genome, that plant is often capable of reproducing with other, non-GM corn plants, including neighbouring traditional corn varieties. Such hybridization events allow for genetic flow, or mixing of the gene pools. There is a growing concern that transgenes may provide an unnatural advantage to plants that possess them. Thus, traditional corn populations may become polluted with transgenes as natural and artificial selection promotes these artificial genes. Even after the removal of the source of these transgenes (the GM crop), the rogue genes would continue to spread in the traditional corn populations. Nobody is really sure what impact these transgenes could have on the traditional corn breeds if they spread throughout the traditional corn gene pool.

A number of safeguards to stem transgene escape have been implemented or proposed. Biotech companies are developing transgenic crops that have additional genetic alterations that produce sterile pollen, while hybrid seedlings can be programmed to self-destruct (a.k.a. “suicide seeds”). Farmers may be able to reduce the spread of rogue transgenic plants by separating their transgenic crops from their traditional crops, or ensuring that their traditional seed banks do not become contaminated with transgenic seeds. Governments can play a role by licensing, monitoring, and policing the cultivation of GM crops to reduce the likelihood of unwanted hybridizations.

Figure 1. Transgene escape. Genetic modifications can can find their
way into the natural environment by way of an intermediate hybrid.

While precautions have been taken, these measures are largely untested. The term “transgene escape” has been used to imply that rogue genes can elude such safeguards. Even though transgenes do not possess the will to make that daring “escape” from their GM crop servitude, they may possess qualities that make them prolific and harmful. Fearing the worst, many countries such as Mexico have imposed moratoriums on the cultivation of transgenic crops. Agricultural biotechnology companies have argued that moratoriums are excessive, while environmental agencies claim that the traditional corn races have already suffered from exposure to GM crops. Although protests around ethical and human health issues have tended to dominate the public forum, there is a growing concern for the risks of transgene escape, both into traditional corn and wild maize species.

In the fall of 2001, two researchers, David Quist and Ignacio Chapela, from the University of California (Berkeley) published evidence in Nature that transgenes exist in the traditional corn races of Oaxaca, Mexico. They claim that this provides support that the transgenes have spread into these non-GM corn populations. This startling news provides reason to doubt the effectiveness of existing control measures. Quist and Chapela collected their samples 3 years after the moratorium on GM cultivation was enforced. They suggest that transgenes may be present in samples of traditional corn due to fresh hybridization events with illegally-cultivated GM crops, or the result of “escaped” transgenes that have persisted in traditional corn races since the moratorium was imposed.

Although transgene content in traditional corn races is undisputed, allegations that these transgenes are self-sustaining in traditional corn races, as Quist and Chapela suggest, is a point of great debate. Michael Freeling and colleagues, also from Berkeley, have shown that Quist and Chapela used faulty methodology in demonstrating the spread of transgenes in traditional corn races. Nature was compelled to formally retract the Quist and Chapela publication on the grounds that the authors’ claims exceeded their evidence. Quist and Chapela continue to defend their inferences as the debate on transgene introgression heats up.

Interestingly, Chapela and Freeling have butted heads on biotech issues in the past. Chapela spoke out strongly against a deal Freeling supported between Berkeley and the biotech firm Novartis (now owned by Syngenta) which develops transgenic corn. While Chapela has been labelled an environmentalist, Freeling has allied himself with Syngenta which has an interest in ending the Mexican moratorium on transgenic corn to restore its GM market. Both sides may be viewing and conveying natural phenomenon through political lenses, obscuring the facts about transgene escape.

It is clear that very little is known about the long-term health, socioeconomic, and environmental impacts of GM corn cultivation. Quist and Chapela have shown that the seal has been broken on the genetic barrier between GM corn and traditional corn. We can only speculate about the impact of transgenes on traditional corn varieties until we obtain results from long-term studies.

The people of Oaxaca have long believed that the gift of corn can be revoked if not respected. With so little known about the long-term impacts of GM corn cultivation, there is a global responsibility to ensure that ecosystems, crops and cultures are not subjected to unnecessary risk.


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(artwork by Jiang Long)

About hardyhall

Hardy Hall is an aspiring plant molecular biologist studying the fascinating world of plant immunity and its underlying signalling mechanisms. Hardy enjoys long walks on the beach, orienteering with his miniature dachshund, and gnawing on perplexing biological questions.