The discovery of rogue genetically modified wheat in a farmer's field in Oregon shook global confidence in the safety of America's food supply on Friday.
Billions in food exports were potentially at stake following the disclosure by the US Department of Agriculture of the existence of the GM wheat plants.
The GM variant, developed by the agricultural giant Monsanto, has never been approved for human consumption.
The discovery in Oregon, about a decade after field trials ended in that state, raised concerns among the main buyers of America's wheat abroad, as well as an increasingly active GM movement at home.
The European Union advised member states on Friday to test some wheat shipments from the US. The EU imports more than 1.1m tonnes of wheat a year.
