Stem rust on wheat.
In just one year, ARS geneticist
Les Szabo and colleagues Charles Barnes, a plant pathologist, and lab
technician Kim Nguyen have developed a PCR (polymerase chain reaction)
test to rapidly identify agronomically damaging wheat rusts. Rusts are
fungal plant disease-causing agents. The ones that attack wheat are
known as stem rust, stripe rust, and two species of leaf rust.
Rusts affect just about every plant or crop in the world, with the
notable exception of rice. So far, about 7,000 species of rust have
been identified. The scientists, located at the ARS Cereal Disease Laboratory
on the campus of the University of Minnesota-St. Paul, plan to develop
tests for all the important rusts affecting the major small cereal grain
crops: wheat, barley, rye, and oats.
Extra funding from the U.S. Department of Defensealong with many
previous years of research on rust taxonomyenabled Szabo to develop
the first detection test so quickly. "We had an extensive database
of DNA sequences for most of these species from our previous research,"
he says. "But we had to generate many more to develop this test,
which identifies species by detecting specific DNA sequences within
Close-up of stem rust
The test will likely be used by diagnostic laboratories to analyze
samples from around the country and the world.
Without this test, accurate identification of rusts can be difficult.
"We often tend to assume the identity of a rust based on visible
symptoms and on what's previously been found," says Szabo. "For
example, if it has light-yellow-colored spores, it's assumed to be stripe
rust. But as we have found, this is often not the case." He believes
that with new molecular tools, scientists will find that there are many
more rust species than the currently described 7,000.
Identifying the species is the first phase of Szabo's rust research.
The next phase is identifying subspecies and genetic lineages. "This
would allow us to track the movement of these rusts worldwide and to
immediately recognize types of rust new to this country," Szabo
"That knowledge would help us in many ways, especially in predicting
the subspecies or race of a newly isolated fungus. If we know its race,
we will then know what crop varieties it will attack. This information
will be important to farmers. In addition, we can inform plant breeders
of which races are in this country, which ones may be on the way, and
which crop varieties are in danger, so they can get an early start on
breeding resistant varieties of wheat, barley, and oats."By
Agricultural Research Service Information Staff.
This research is part of Plant Diseases, an ARS National Program
(#303) described on the World Wide Web at www.nps.ars.usda.gov.
Les J. Szabo, Charles Barnes,
and Kim P. Nguyen are with the USDA-ARS Cereal
Disease Laboratory, 1551 Lindig Ave., St. Paul, MN 55108; phone
(612) 625-3780, fax (651) 649-5054.
"Identifying Rust EnemiesPrecisely" was published
in the June
2004 issue of Agricultural Research magazine.