Madison, Wisconsin
January 28, 2008
More than 99 percent of all modern
potato varieties planted today are the direct descendents of
varieties that once grew in the lowlands of south-central Chile.
How Chilean germplasm came to dominate the modern potato-which
spread worldwide from Europe-has been the subject of a long,
contentious debate among scientists.
While some plant scientists have maintained that Chilean
potatoes were the first to be planted in Europe, a more widely
accepted story holds that European potatoes were originally
descended from plants grown high in the Andes mountains between
eastern Venezuela and northern Argentina. According to this
theory, Andean potatoes were wiped out during the Great Irish
Potato Famine, the 19th-century late-blight epidemic that
devastated potato fields across Europe, initiating the import of
Chilean varieties to re-establish the crop.
In a report published today in the American Journal of Botany,
University of Wisconsin-Madison
researchers Mercedes Ames and David Spooner say both theories
are wrong. By analyzing the DNA of historical potato specimens,
the researchers found that both Chilean and Andean potatoes were
grown in Europe decades before and decades after the famine, the
first direct evidence that the potatoes were grown
simultaneously in Europe.
"Basically, we found that the Andean potatoes got to Europe
first, around 1700. However, Chilean potatoes were starting to
get popular there 34 years before the late blight epidemic,"
says Ames, a graduate student in UW-Madison's plant breeding and
plant genetics program. The results also show that Andean
potatoes grew as late as 1892 in Europe, proving they weren't
polished off by the late blight epidemic-and that they grew side
by side with Chilean potatoes for many decades before the
Chilean types became dominant.
To start the project, which was funded by the National Science
Foundation, Ames visited herbaria throughout Europe in search of
early potato specimens. She requested hole-punch sized samples
of dried leaf tissue from appropriate specimens be sent to
Madison for study, eventually ending up with material from 64
potato plants grown between 1700 and 1910.
"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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