Solving
the specifics of the potato blight is academically important but that
we were able to recover intact DNA from samples 150 years old is
extremely good news. From the late eighteenth century through recent
times, biology was about amassing huge collections of plants and
critters, all maintained and stored in museums and libraries to this
day.
That
is why I am optimistic that recovery of much of our extinct fauna and
flora happens to be plausible. Most of it went extinct with contact,
not so much us as our pests and particularly the rat.
Extinction
recovery is still a massive enterprise but no longer unimaginable.
We will have to master the rat before we get too far into it but you
can see the light at the end of the tunnel. I do expect to see the
establishment of many unique island refugia packed with many unique
and obscure species fully restored. It will not be Jurassic Park but
no matter.
May 21, 2013 — An
international team of scientists reveals that a unique strain of
potato blight they call HERB-1 triggered the Irish potato famine of
the mid-nineteenth century.
It is the first time
scientists have decoded the genome of a plant pathogen and its plant
host from dried herbarium samples. This opens up a new area of
research to understand how pathogens evolve and how human activity
impacts the spread of plant disease.
Phytophthora
infestans changed the course of history. Even today, the Irish
population has still not recovered to pre-famine levels. "We
have finally discovered the identity of the exact strain that caused
all this havoc," says Hernán Burbano from the Max Planck
Institute for Developmental Biology.
For research to be
published in eLife, a team of molecular biologists from Europe
and the US reconstructed the spread of the potato blight pathogen
from dried plants. Although these were 170 to 120 years old, they
were found to have many intact pieces of DNA.
"Herbaria
represent a rich and untapped source from which we can learn a
tremendous amount about the historical distribution of plants and
their pests -- and also about the history of the people who grew
these plants," according to Kentaro Yoshida from The Sainsbury
Laboratory in Norwich.
The researchers
examined the historical spread of the fungus-like
oomycete Phytophthora infestans, known as the Irish potato
famine pathogen. A strain called US-1 was long thought to have been
the cause of the fatal outbreak. The current study concludes that a
strain new to science was responsible. While more closely related to
the US-1 strain than to other modern strains, it is unique. "Both
strains seem to have separated from each other only years before the
first major outbreak in Europe," says Burbano.
The researchers
compared the historic samples with modern strains from Europe, Africa
and the Americas as well as two closely related Phytophthora species.
The scientists were able to estimate with confidence when the
various Phytophthorastrains diverged from each other during
evolutionary time. The HERB-1 strain of Phytophthora
infestans likely emerged in the early 1800s and continued its
global conquest throughout the 19th century. Only in the
twentieth century, after new potato varieties were introduced, was
HERB-1 replaced by anotherPhytophthora infestans strain,
US-1.
The scientists found
several connections with historic events. The first contact between
Europeans and Americans in Mexico in the sixteenth century coincides
with a remarkable increase in the genetic diversity of Phytophthora.
The social upheaval during that time may have led to a spread of the
pathogen from its center of origin in Toluca Valley, Mexico. This in
turn would have accelerated its evolution.
The international team
came to these conclusions after deciphering the entire genomes of 11
historical samples ofPhytophthora infestans from potato
leaves collected over more than 50 years. These came from Ireland,
the UK, Europe and North America and had been preserved in the
herbaria of the Botanical State Collection Munich and the Kew Gardens
in London.
"Both herbaria
placed a great deal of confidence in our abilities and were very
generous in providing the dried plants," said Marco Thines from
the Senckenberg Museum and Goethe University in Frankfurt, one of the
co-authors of this study. "The degree of DNA preservation in the
herbarium samples really surprised us," adds Johannes Krause
from the University of Tübingen, another co-author. Because of the
remarkable DNA quality and quantity in the herbarium samples, the
research team could evaluate the entire genome of Phytophthora
infestans and its host, the potato, within just a few weeks.
Crop breeding methods
may impact on the evolution of pathogens. This study directly
documents the effect of plant breeding on the genetic makeup of a
pathogen. "Perhaps this strain became extinct when the first
resistant potato varieties were bred at the beginning of the
twentieth century," speculates Yoshida. "What is for
certain is that these findings will greatly help us to understand the
dynamics of emerging pathogens. This type of work paves the way for
the discovery of many more treasures of knowledge hidden in
herbaria."
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