MADISON - Humans have cultivated potatoes for millennia, but there hasbeen great controversy about the ubiquitous vegetable's origins. Thisweek, writing in the Proceedings of the National Academies of Sciences,a team led by a USDA potato taxonomist stationed at the University ofWisconsin-Madison has for the first time demonstrated a single originin southern Peru for the cultivated potato.
The scientists analyzed DNA markers in 261 wild and 98 cultivatedpotato varieties to assess whether the domestic potato arose from asingle wild progenitor or whether it arose multiple times - and theresults were clear, says David Spooner, the USDA research scientist wholed the study.
"In contrast to all prior hypotheses of multiple origins of thecultivated potato, we have identified a single origin from a broad areaof southern Peru," says Spooner, who is also a UW-Madison professor ofhorticulture. "The multiple-origins theory was based in part on thebroad distribution of potatoes from north to south across manydifferent habitats, through morphological resemblance of different wildspecies to cultivated species, and through other data. Our DNA data,however, shows that in fact all cultivated potatoes can be traced backto a single origin in southern Peru."
The earliest archaeological evidence suggests that potatoeswere domesticated from wild relatives by indigenous agriculturalistsmore than 7,000 years ago, says Spooner. Today, the potato - aninternational dietary staple - is a major crop in both the UnitedStates and in Wisconsin, which is fourth in the nation for potatoproduction.
Potato diseases such as late blight can cause significant economic damage to farmers in America and throughout the world.
"As a taxonomist, my job is to help determine what is a species and toclassify those species into related groups," Spooner explains. "Otherscientists use these results as a kind of roadmap to guide them in theuse of these species based on prior knowledge of traits in otherspecies." Spooner spends about two months each year trekking throughthe mountains of South America, collecting and identifying wildpotatoes and researching them.
"When researchers discover an important trait - for example, that acertain species is resistant to disease - then everything related tothat species becomes potentially useful," Spooner says. "We can screensamples to see if related germplasm has similar resistance, in whichcase we may be able to guide plant breeders to germplasm to use inbreeding programs."
And beyond the agricultural benefits, Spooner's study hashelped to rewrite a small but important chapter of evolutionaryhistory.
"Books are written about questions of how crops originate," hesays. "Sometimes statements are repeated so often that they areaccepted as fact. This is a way to get people to reconsider long-heldassumptions of the origin of the potato, and stimulate us to reconsiderthe origins of other crops using new methods."
Spooner's collaborators included colleagues from the GenomeDynamics Programme at the Scottish Crop Research Institute in Scotland.The work was supported financially by the USDA Agricultural ResearchService, by the USDA's Foreign Agricultural Service, and by theScottish Executive Environment and Rural Affairs Department.
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