Transgenes spread to wild crops in Mexico: Unknown
In 2000, some rural farmers in the mountains of Oaxaca, Mexico, wanted to gain organic certification for the maize (corn) they grew and sold in the hope of generating extra income. David Quist, then a microbial ecologist at the University of California, Berkeley, agreed to help in exchange for access to their lands for a research project. But Quist’s genetic analyses uncovered a surprise: the locally produced maize contained a segment of the DNA used to spur expression of transgenes in Monsanto’s glyphosate-tolerant and insect-resistant maize.
GM crops are not approved for commercial production in Mexico. So the transgenes probably came from GM crops imported from the United States for consumption and planted by local farmers who probably didn’t know that the seeds were transgenic. Quist speculated at the time that the local maize probably cross-bred with these GM varieties, thereby picking up the transgenic DNA.
When the discovery was published in Nature, a media and political circus descended on Oaxaca. Many vilified Monsanto for contaminating maize at its historic origin — a place where the crop was considered sacred. And Quist’s study came under fire for technical deficiencies, including problems with the methods used to detect the transgenes and the authors’ conclusion that transgenes can fragment and scatter throughout the genome. Nature eventually withdrew support for the paper but stopped short of retracting it. “The evidence available is not sufficient to justify the publication of the original paper,” read an editorial footnote to a critique of the research published in 2002.
Since then, few rigorous studies of transgene flow into Mexican maize have been published, owing mainly to a dearth of research funding, and they show mixed results. In 2003–04, Allison Snow, a plant ecologist at Ohio State University in Columbus, sampled 870 plants taken from 125 fields in Oaxaca and found no transgenic sequences in maize seeds.
But in 2009, a study led by Elena Alvarez-Buylla, a molecular ecologist at the National Autonomous University of Mexico in Mexico City, and Alma Piñeyro-Nelson, a plant molecular geneticist now at the University of California, Berkeley, found the same transgenes as Quist in three samples taken from 23 sites in Oaxaca in 2001, and in two samples taken from those sites in 2004. In another study, Alvarez-Buylla and her co-authors found evidence of transgenes in a small percentage of seeds from 1,765 households across Mexico. Other studies conducted within local communities have found transgenes more consistently, but few have been published.
Snow and Alvarez-Buylla agree that differences in sampling methods can lead to discrepancies in transgene detection. “We sampled different fields,” says Snow. “They found them but we didn’t.”
The scientific community remains split on whether transgenes have infiltrated maize populations in Mexico, even as the country grapples with whether to approve commercialization of Bt maize.
“It seems inevitable that there will be a movement of transgenes into local maize crops,” says Snow. “There is some proof that it is happening, but it is very difficult to say how common it is or what are the consequences.” Alvarez-Buylla argues that the spread of transgenes will harm the health of Mexican maize and change characteristics, such as a variety’s look and taste, that are important to rural farmers. Once the transgenes are present, it will be very difficult, if not impossible, to get rid of them, she says. Critics speculate that GM traits that accumulate in the genomes of local maize populations over time could eventually affect plant fitness by using up energy and resources or by disrupting metabolic processes, for example.