Using DNA, scientists hunt for the roots of the mod...(to specimens. She requested hole-punch s...)

"Some of these samples were over 300 years old and not ideally preserved," says Spooner, a professor of horticulture and USDA researcher who is the paper's corresponding author. "It took considerable innovation for Mercedes to work out the correct technique to get DNA from them."

After successfully extracting DNA from 49 samples, Ames analyzed each using a DNA marker that distinguishes between upland Andean and lowland Chilean potato types. The result is a biochemical record of ancestry, which Spooner says adds hard evidence to a debate often premised on guesswork.

"The problem with these two theories is that they rely on inferences based on the morphology of old plant samples, as well as inferences based on historical records about day-length adaptation, shipping routes, and the role of the late blight epidemic," he says. "Our work is the first direct evidence-as opposed to the inferential evidence used in prior studies-on the origin of the European potato because the herbarium specimens we used are like fossils."

Spooner notes that this type of analysis could help set the record straight for many other crop species. "Potato is one of the prominent stories in crop evolution books," says Spooner. "Because of Mercedes's work, they're going to have to rewrite the textbooks."

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