US scientists have found that all modern varieties of potatoes can be traced back to a single source - a spud grown in Peru over 7,000 years ago. It had been believed potatoes had a much wider region of origin, stretching from Peru to northern Argentina. The team, led by Dr David Spooner of the University of Wisconsin-Madison, analysed the DNA of about 360 potatoes, both wild and cultivated. Some 300 million tonnes of potatoes are produced around the world every year. The study was sponsored by the US Department of Agriculture. Dr Spooner, a professor of horticulture, said archaeological...