Humans have cultivated potatoes for millennia, but there has been great controversy about the ubiquitous vegetable's origins. This week, writing in the Proceedings of the National Academies of Sciences, a team led by a USDA potato taxonomist stationed at the University of Wisconsin-Madison has for the first time demonstrated a single origin in southern Peru for the cultivated potato.

The scientists analyzed DNA markers in 261 wild and 98 cultivated potato varieties to assess whether the domestic potato arose from a single wild progenitor or whether it arose multiple times - and the results were clear, says David Spooner, the USDA research scientist who led the study.

"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," says Spooner, who is also a UW-Madison professor of horticulture. "The multiple-origins theory was based in part on the broad distribution of potatoes from north to south across many different habitats, through morphological resemblance of different wild species to cultivated species, and through other data. Our DNA data, however, shows that in fact all cultivated potatoes can be traced back to a single origin in southern Peru."

The earliest archaeological evidence suggests that potatoes were domesticated from wild relatives by indigenous agriculturalists more than 7,000 years ago, says Spooner. Today, the potato - an international dietary staple - is a major crop in both the United States and in Wisconsin, which is fourth in the nation for potato production.