Credit: Michael Farrelly, AFSA
By Timothy A. Wise
CAMBRIDGE, MA., Apr 30 2025 – On March 17, Mexican President Claudia Scheinbaum signed into law a constitutional reform banning the cultivation of genetically modified (GM) corn. The action followed a December ruling by a trade tribunal, under the U.S.-Mexico-Canada (USMCA) trade agreement, in favor of a U.S. complaint that Mexico’s 2023 presidential decree, with broader restrictions on the consumption of GM corn, constituted an unfair trade practice by prohibiting the use of GM corn in tortillas.
The Mexican government publicly disagreed with the ruling, claiming that the three arbitrators had failed to consider the scientific evidence Mexico presented in the yearlong case. But the government chose to comply, rescinding the three specific parts of the decree deemed to limit future GM corn imports. Still, the government left intact the decree’s measures phasing out the use of the herbicide glyphosate, establishing a protocol for tracking GM corn imports into the country, and banning the cultivation of GM corn in the country.
The constitutional amendment enshrines that last measure in a more permanent manner. While GM corn has faced planting restrictions for more than a decade, the constitutional ban represents an important act of resistance and sovereignty, particularly in light of the flawed decision by the tribunal.
Trade panel fails to consider evidence
Corn is central to Mexico’s agriculture, cuisine, nutrition, and culture. Mexico is the center of origin for corn, where the crop was domesticated thousands of years ago. It remains at the core of the country’s farming, diet, and culture. As President Sheinbaum acknowledged in approving the constitutional ban on GM corn cultivation, “Sin maiz no hay pais” – without corn there is no country.
In defense of Mexico’s 2023 decree, the panel acknowledged that the government presented scientific evidence from qualified and reputable sources of “risks to human health arising from the direct consumption of GM corn grain in Mexico, and risks to native corn of transgenic contamination arising from the unintentional, unauthorized, and uncontrolled spread of GM corn in Mexico.” (That evidence is summarized in an extensive publication from Mexico’s national science agency.)
The trade tribunal dismissed concerns about such risks in its ruling, essentially giving itself a pass on reviewing the scientific evidence of human-health risks by arguing that Mexico had not conducted an approved risk assessment “based on relevant scientific principles,” a reference to prevailing international codes for such processes.
The panel also failed to evaluate the risks to native corn. Mexico presented strong evidence that GM corn has cross-pollinated native corn varieties, gene flow that threatens to undermine the genetic integrity of the country’s 64 “landraces” and more than 22,000 varieties adapted by farmers over millennia to different soils, altitudes, climates, foods, and customs.
The tribunal argued that no special protection from GM corn was needed because gene flow already takes place from non-GM hybrid varieties of corn, and GM contamination is no different from non-GM gene flow. “Mexico has not demonstrated how the threat to the traditions and livelihoods of indigenous and farming communities from GM corn is greater than the threat posed by non-native, non-GM corn,” the panel wrote. Cross-pollination from hybrid corn “could equally threaten the genetic integrity of native corn.”
Equating contamination from GM corn with that of hybrid corn is a serious misreading of the science and of Mexico’s culture. GMOs by definition – and by explicit definitions in the constitutional amendment – involve crossing species boundaries, introducing, for example, a gene from a bacterium into a corn plant to repel insects. In contrast, hybrid corn is produced by cross-breeding different corn varieties, the resulting offspring remaining pure corn, with no non-corn genes in its DNA.
Mexican farmers have a long history of developing some of their own cross-pollinated varieties, intentionally combining a native variety with a hybrid that has properties the farmer desires. Such cross-pollination has nothing in common with unwanted contamination from GM corn, imposed on farmers without their informed consent. They call it “genetic pollution.”
It can pose a long-term risk to native varieties. Transgenic traits do not always reveal themselves after contamination. That means farmers can unknowingly spread such contamination from their pollen year after year to other corn plants. Mexican researchers discovered such contamination in their 2013 survey of native corn varieties. Biotechnologist Antonio Serratos reported that some of the native varieties he found even within Mexico City had transgenic traits in their DNA.
“In Mexican fields, transgenic native maize is being created,” he told me at the time. ”If [GM] maize seeds are sold or exchanged, the contamination will grow exponentially. That is the point of no return.”
Seed-sharing under threat
The tribunal’s alternative recommendation for controlling unwanted gene flow suggested that “the informal seed exchange practices of indigenous and farming communities” was one of the “underlying issues” Mexico should address to prevent contamination instead of restricting imports.
Limiting seed-sharing is entirely at odds with the science of seed diversity and evolution, says researcher Erica Hagman, who helped prepare Mexico’s defense in the USMCA dispute. Mexico’s rich corn diversity is the direct result of millennia of adaptive practices by farmers in their fields. The tribunal’s suggestion that Mexico should limit such seed-sharing to prevent GM corn contamination runs counter to the practices of in situ conservation of agricultural biodiversity.
Mexico’s constitutional ban on GM corn cultivation ensures that such misguided reasoning will not guide public policy. The amendment was strengthened by proposals from civil society that extended the ban to new genetically engineered seeds by banning any crops “produced with techniques that overcome the natural barriers of reproduction or recombination, such as transgenics.” This limits some of the new generations of genetically engineered crops.
While the constitutional reform does not include some of the original language restricting GM corn consumption, no doubt in deference to the trade ruling, the final version shows a clear preference for non-GM crops, leaving the door open to tighter regulation.
Tania Monserrat Téllez from the Sin Maíz No Hay País coalition called the reform “a major step forward for the defense of native corn varieties, the health of the Mexican population, and the protection of Mexico’s biocultural heritage associated with corn.”
Timothy A. Wise is the author of Eating Tomorrow: Agribusiness, Family Farmers, and the Battle for the Future of Food (New Press 2019) and a researcher at Tufts University’s Global Development and Environment Institute.
IPS UN Bureau
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