Seed exchange moves transgenes through Mexican maize


DAVIS, Calif. — The appearance of genetically modified proteins in maize seed stocks throughout Mexico paints a curious pattern that suggests why efforts to prevent the flow of transgenic plant material into that country could fail, reports a team of researchers in Mexico and at UC Davis.

The researchers hope their findings, published online in the journal Public Library of Science, will help guide development of methods and public policies for regulating the movement of genetically modified plant material into local seed stocks in centers of crop origin and diversity.


The research team, led by UC Davis agricultural economist and plant biologist George A. Dyer, used enzyme-based tests, mathematical models of crop populations and knowledge of established seed-use patterns to analyze maize seed stocks in Mexico for the presence of proteins from genetically modified, or transgenic, maize varieties.

“We found that, nationwide, 5 percent of Mexico’s maize seed stocks contained transgenic proteins by 2002,” Dyer said. “That nationwide average included a surprising 13 percent in southeast Mexico and 3 percent in the west-central part of the country.”

Might explain

Dyer noted the possible spread of genetically modified seed and grain from the U.S. might explain how the transgenic plant material found its way into maize seed stocks in Mexico’s west-central region, where informal introduction and sharing of improved seed is quite common.

But that route of introduction would not account for the strong presence of transgenic seed in the country’s southwest area, where use of foreign seed is fairly uncommon.

Gene flow controversy

Although there have been no authorized commercial releases of genetically modified corn or other maize species in Mexico, which is the birthplace of maize, the potential for gene flow from transgenic maize into Mexico has been controversial throughout the past decade.

In 2001, a highly publicized study by UC Berkeley researchers first reported the appearance of proteins from genetically modified corn in native maize varieties in Oaxaca, Mexico.

That study raised concerns that the flow of genes from the transgenic varieties threatened the genetic diversity embodied in Mexico’s native maize species.

However, the study’s methods were criticized and its results questioned.

Dyer and colleagues addressed outstanding methodological issues in two previous papers in the scientific journals Proceedings of the National Academy of Science in 2008 and Molecular Ecology in 2009.

The first paper discussed how farmers’ practices impact the evolution and diversity of maize in Mexico, and the second paper suggested monitoring protocols for detecting the presence of transgenes among native maize varieties.

Findings on seed use

The research team’s third article, published in the Public Library of Science, builds on the two previous papers, with special attention to how seeds are managed and shared in Mexico.

In this recent study, the researchers found:

Informal seed exchange between farmers was the main source of seed dispersal across Mexico and was more important in the southeast than in the north;

Seed obtained from neighboring farmers was more likely to be saved from year to year, while seed that was imported or obtained from government programs was more likely to be replaced with other seed in succeeding years; and

Marked differences in the rate of spread of proteins from genetically modified maize in different areas of Mexico suggest the transgenic material was dispersed through different routes in each region.

Government regulation

“Many governments in developing countries are planning to regulate the release of genetically modified crops,” Dyer said. “In Mexico, current regulatory efforts assume that the spread of genes from genetically modified plants into native plants can be prevented or reversed by restricting commercial release of genetically modified varieties to areas of industrialized agriculture,” he said.

“Our study, however, suggests that this approach might be ineffective because controlling or even tracking the flow of grain within Mexico poses such a formidable challenge.”

He noted, in order to develop systems for protecting genetic diversity in areas where native crops originated, further research is needed to explore how genetic material flows through both formal and informal seed and grain systems.


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