Several plant scientists have questioned conclusions US seeds giant Monsanto drew from its investigation of an escaped gene-altered wheat variety and said there is still a risk that rogue grain is in the seed supply.
In its first detailed response to the announcement that a genetically modified wheat not approved for use was found growing in an American farmer's field, Monsanto said that it tested 31,200 seed samples in the US states of Oregon, where the wheat was found, and Washington and found no contamination.
That's not enough to convince some researchers that this genetic modification, not cleared for commercial sale, won't be found in some wheat seeds.
"We don't know where in the whole chain it is," said Carol Mallory-Smith, the weed science professor at Oregon State University who tested the initial wheat plants. "I don't know how Monsanto can declare anything. We had these plants in the field."
The US Department of Agriculture is investigating how the wheat showed up eight years after the company ended field tests. It was found growing on about 1 per cent of the farmer's 51-hectare field, and he submitted it to Oregon State for testing after an Monsanto's Roundup herbicide didn't kill it.
Monsanto's tests show the genetically modified variety isn't present in the types of seeds planted on the Oregon farm or in wheat seed common in the region, Monsanto chief technology officer Robb Fraley said.
In previous cases, such as during the outbreak of herbicide-resistant weeds in recent years, Monsanto has played down the risks, said Doug Gurian-Sherman, senior scientist at the Union of Concerned Scientists, which is critical of Monsanto's genetically modified research.