Modern potato had roots in Peru

Until now it was believed potatoes had no single origin

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 finds had shown potatoes were being grown in Peru by farmers "more than 7,000 years ago".

"In contrast to all prior hypotheses of multiple origins of the cultivated potato, we have identified a single origin from a broad area of southern Peru," said the scientist, who spends two months a year collecting wild potatoes on treks in South America's mountainous regions.

Potatoes were brought back to Spain by the conquistadors around 1570, and spread throughout Europe.

They were later introduced in North America by British colonists.