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Scientific Collections: Mission-Critical Resources for Federal Science Agencies
Combating agricultural threats
For many people, oranges in Christmas stockings are a family tra-
dition. Clementine oranges are especially prized because they are
sweet and easy to peel. Just before Christmas 2001, USDA prohibited
imports of Clementine oranges from Spain because Mediterranean
fruit fly larvae had been found in several shipments. The Mediter-
ranean fruit fly is not simply a nuisance, but one of the world's most
harmful agricultural pests. It requires massive and expensive eradica-
tion programs to protect fruit production from destruction (in Califor-
nia alone, the 2005 value of vulnerable fruits was $9.5 billion). By
using USDA's comprehensive fruit fly collection, scientists have de-veloped an expert system that
allows port inspectors to rap-
idly and reliably identify fruit
flies in the shipments they in-
spect. And if the flies stump the
inspectors, they can be shipped
to USDA's Systematic Entomol-
ogy Lab where experts can use
the collection to provide an
identification within 24 hours
(ITAP 2008).Keeping International Markets Open
Like all crops, wheat is vulnerable to diseases that can kill it outright,
reduce its yield, or simply make it inedible. One such disease is caused by
a fungus called Karnal bunt, which makes wheat smell and taste like rotten
fish. Even a tiny amount can contaminate an entire railcar full of wheat.
In 1996, Karnal bunt spores blew in on
the wind from Mexico to Arizona, and
scattered reports of wheat infested with
Karnal bunt began to appear. Reports
of Karnal bunt from wheat producing
areas all around the United States soon
followed. Other countries embargoed
U.S. wheat and the $6 billion-a-year Wheat Harvest.
wheat export market was faced with Photo courtesy of ARS. (image no. K1441-5)
a looming economic disaster.
Karnal bunt has look-alike cousins that can't be readily distinguished from
it, even under a microscope. For this reason, investigators were relying on
a DNA test to identify the fungus that was infecting the U.S. wheat. Using
the USDA's National Fungus Collection for comparison, a USDA scientist
discovered that the fungus being identified as Karnal bunt was really a
harmless rye grass fungus. By using the collection to develop a more ac-
curate DNA test, the scientist determined that Karnal bunt was limited to a
small area in Arizona. Exports of wheat from the rest of the country could
safely continue.
In 2005, the Algerian government claimed that a shipment of U.S. wheat
was contaminated with Karnal bunt, raising the prospect of trade embargoes
again. A scientist traveled to Algeria to investigate and determined that the
shipment was not, in fact, contaminated, saving the $70 million annual U.S.
wheat export market in Algeria. USDA's fungus collections provide a way to
distinguish false alarms from real infestations, thereby ensuring US access to
global markets.
When greatly magnified, a ryegrass bunt spore from Tennessee (right) displays thicker,
wider ridges and grooves than those of a Karnal bunt spore (left) .
Both specimens are from the National Fungus Collection. Both photos by Jim Plaskow-
itz, Courtesy of ARS
H 161;,
15
Male medfly resting on a leaf.
Photo by Scott Bauer Courtesy ofARSOld Specimens, New Solutions
Citrus bacterial canker is a devastating bacterial disease of citrus
trees that threatens the U.S. citrus industry, and it's causing major
problems in Florida. As the disease continues to spread around the
world, it's critical to understand where the disease came from and
the route of spread in order to develop appropriate methods for
control or prevention. How to go back and look at this over time?
Herbarium specimens in the National Fungus Collection, collected
from Japan and Florida in the early 1900s, proved to be the key.
These citrus tree samples were collected because they were infected
with fungal diseases; bacterial diseases were not well known at the
time. Techniques for analyzing DNA were developed much later,
providing new information on bacterial infections. A century after
the specimens were collected, scientists found the citrus canker
bacteria on them as well, allowing them to unravel the history of the
disease and pin down its source. Neither the presence of the bac-
teria nor the existence of DNA, much less ways to analyze it, were
envisioned when the leaf samples were collected. (Li et al. 2007).
EE.t Eir1il
Citrus specimens
that had symptoms
Si of citrus canker were
L Z preserved with date
and place of origin
over the last century.
The USDA ARS has
741 samples like these
till I originally collected
from more than 30
. 0 countries during the
. .. .. - pI 20th century.Dunn
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National Science and Technology Council (U.S.). Committee on Science, Interagency Working Group on Scientific Collections. Scientific Collections: Mission-Critical Infrastructure for Federal Science Agencies, text, December 23, 2008; Washington D.C.. (https://digital.library.unt.edu/ark:/67531/metadc25984/m1/15/: accessed April 19, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; .