Mexico is ill-equipped to protect its natural maize varieties from transgenes, say scientists concerned about the planting of genetically modified (GM) maize in the country's northern region.
More than 2,000 scientists have signed a petition calling for the trials, run by agricultural companies Dow Agri-Sciences and Monsanto, to be blocked.
Both companies have received government approval to plant GM maize in the past month. Mexico had banned the planting of GM maize for 11 years.
Government officials say measures are in place to prevent gene flow from the crops to natural varieties. Plantations will be small, planting will occur at different times from natural varieties and farmers will be asked about any negative effects of GM maize on their crops.
But José Sarukhán, a prominent Mexican biologist, said the country is unable to safely carry out GM planting.
"If Mexico experimentally plants transgenic maize it should be done with ideal experiments and a great capacity to monitor them — but we don't have either," he said.
One concern is over Genetic ID, the US company hired to train staff for two transgene-testing laboratories in Mexico City.
Whether the firm has sensitive enough methods to detect transgenes has been questioned by Elena Alvarez-Buylla, a geneticist at the Institute of Ecology in Mexico City, whose team reported this year that GeneticID failed to detect transgenes in blinded samples.
GeneticID said that the results were because of sample contamination.