i think i've just learn't more about potatoes, then i ever needed to know! but couldn't find an answer, the closest i got was this
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.
source the online potato museum - i kid ye not!