Investigations continued this week into how unauthorised genetically modified wheat ended up on in Oregon.
No varieties of GM wheat have been cleared for commercial use anywhere in the world. The wheat plants in question are believed to be the legacy of a research programme that was abandoned nine years ago. How and why they have resurfaced is unclear.
The discovery last week triggered an international reaction, with both South Korea and Japan temporarily suspending import of US wheat. South Korea has also begun testing existing wheat imports from the US for signs of GM wheat, with no positive results so far.