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From:
Subject: Testing Links Potato Famine to an Origin in the Andes
Date: Thu, 07 Jun 2001 09:39:13 -0500

To List:

I thought that the list might like to see this article from
the NY Times

Best Regards,

Mike McGraw
Austin, TX



June 7, 2001

Testing Links Potato Famine to an Origin in the Andes

By NICHOLAS WADE

A delicate piece of detective work in the collections of the
Royal Botanic
Gardens at Kew has started to cast light on the origins of the
blight that
caused the Irish potato famines a century and a half ago.

Analysis of DNA from stricken potato leaves has confirmed that
the pathogen was a
fungus known as Phytophthora infestans, but suggests that it
did not originate in the
Toluca Valley of Mexico, a hot spot of different strains of
the blight that has been
proposed as the most likely source. Instead, researchers
theorize, it may have arisen
in the ancestral home of the potato in the Andean highlands of
South America.

The Irish potato famines lasted from 1845 to 1860, during
which about a million of
Ireland's 8 million people starved to death and 1.5 million
emigrated, mostly to the
United States.

Diseased leaves deposited at the time in botanical collections
have been analyzed by
Dr. Jean B. Ristaino, a plant pathologist at North Carolina
State University in
Raleigh.

She and colleagues report in the current issue of Nature that
they were able to
extract DNA from samples collected in Ireland, Britain and
France between 1845
and 1847. In the right conditions, DNA can survive for many
years after the death
of the living cells that make it.

The samples lack the genetic signature of a widespread strain
of the fungus, US-1,
which has been assumed from its worldwide distribution to have
descended from the
19th- century blight that struck Ireland and much of Europe.
The US-1 strain is
thought to have originated in Mexico because that is where the
known diversity of
blight strains is highest.

Because the potato famine samples differ from the US-1 strain,
Dr. Ristaino and her
colleagues suggest that it is likely to have come from the
Andean highlands. It is a
well known phenomenon in biology for a pathogen and its host
to evolve together.

A South American source was proposed by several people who
studied the blight in
the 19th century, including Charles Darwin.

He had collected potato tubers from Chile in 1835 during the
voyage of the Beagle
that led him to propose his theory of evolution by natural
selection. Darwin was very
concerned about the blight, Dr. Ristaino said, and gave Irish
potato breeders £100
of his own money to support efforts to develop resistant
strains.

He also hoped that the tubers from Chile might be naturally
resistant to the blight and
asked his cousin, William Darwin Fox, to grow them. But they
all succumbed to the
blight, which was endemic in England as well as Ireland, Dr.
Ristaino said.

There were many hints available at the time pointing to South
America as a possible
source of the blight, she said: European potato crops had been
wiped out earlier in
the century by a different disease, caused by a fungus called
Fusarium, and were
replaced with varieties from Peru.

There was also a vigorous trade in bat guano fertilizer
between Peru and Ireland,
and that material could have transported the blight.

Dr. Ristaino said more strains of the blight needed to be
sampled worldwide to help
pinpoint the origin of the one she had found in the herbarium
samples.

"There's a real treasure trove of materials over there," she
said, referring to the Kew
herbarium collections outside London.

"There are many other pathogens hidden away on the shelves.
You can capture a
whole window into past epidemics."

In a commentary in Nature, Dr. Nicholas P. Money, a botanist
at Miami University
in Oxford, Ohio, described Dr. Ristaino's analysis as "a
remarkable piece of
molecular detective work."

Dr. Stephen B. Goodwin, one of the biologists who discovered
that the US-1 strain
of blight now dominates the globe, said his theory of its
being the cause of the Irish
potato famine now seemed incorrect.

"Too bad it wasn't true," he said, "but that's the way it goes
sometime. It was a great
hypothesis."

Dr. Goodwin, a Department of Agriculture plant pathologist who
teaches at Purdue
University, said that the potato family had two centers of
diversity, one in Mexico
and one in Peru, but that the blight itself is far more
diverse in the Mexican center
and is likely to have evolved there.

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