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Yeast Debuts in Tests on Controlling Wheat Scab
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To reduce the severity of Fusarium
head blight, Ohio State University
plant pathologist Naseem Khan
sprays a solution containing
Bacillus bacteria cells onto
wheat heads.
(K9452-6)
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Summer 2001 marks the beginning of
the first wide-scale field tests that will compare chemical power to biological
strategies for controlling Fusarium head blight, the disease also called scab.
Since early spring, ARS researchers led
by plant pathologist David A. Schisler have been busy supplying 13 cooperating
state agricultural experiment stations with cultures of the yeast
Cryptococcus nodaensis as a biological control standard-bearer for the
test.
Schisler and his colleagues at the National Center for Agricultural Utilization
Research (NCAUR), in Peoria, Illinois, grow the yeast in 20-liter bioreactors.
Formerly known as fermentors, bioreactors provide precisely the environment of
nutrients, aeration, temperatures, and other conditions needed to help microbes
such as C. nodaensis reproduce at top speed. After about 48 hours, the
researchers empty the bioreactors and process and freeze the yeasts for field
tests. One-liter batches are used to start the next round of fermentation.
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Plant pathologist David
Schisler examines two wheat
seed heads inoculated with
the causal agent of scab.
The one on the right was
sprayed with biocontrol
microbes that greatly
reduced disease symptoms.
(K9450-16)
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Caused by the fungus Fusarium
graminearum, the disease is named "scab" because of the
whitish-grey discoloration that forms on wheat or barley grains. In the past
decade, farm losses to scab have been estimated at more than $3 billion in the
United States. Outbreaks in wheat and barley have been especially severe in
Illinois, Indiana, Michigan, Minnesota, North Dakota, Ohio, and South Dakota.
F. graminearum can also cause root, stalk, and ear rots in corn.
With plant pathologists Michael J. Boehm and Naseem I. Khan of Ohio State
University (OSU), Schisler has screened nearly a thousand yeasts and bacteria
for their fungus-control ability. The U.S. Department of Agriculture (USDA) has
applied for a patent jointly with OSU on seven microbes presently considered
most promising. Applied to wheat as it begins to flower, the beneficial
microbes, according to one theory, produce chemicals that inhibit growth of the
disease fungi. Or in some cases, the "good guy" microbes may gobble
up nutrients that ooze from the anthers—male organs in the seed head. When
the wind blows Fusarium spores onto the anthers, little if any
nourishment is left. The culprit fungi may then never gain a foothold to damage
the developing kernel deeper inside the flower. |
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Using a video monitor and a light
microscope, technician Jennifer
Ierulli studies yeast cells while
several bud to form new cells.
(K9451-1)
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Wheat scab research at NCAUR and OSU
is funded in part by a USDA National Research Initiative Grant. Some of the
research is being funded by the Dakota Growers Pasta Company. Durum wheat, used
to make pasta, is produced mainly in North and South Dakota and Canada. The
company became interested in funding biological control of scab research after
seeing results of preliminary field trials.
If the research continues to underscore the microbes' potential, a company may
decide to license them and do what's needed to make them commercially
successful. Such efforts would involve research on scaled-up production and
automated processing, some of which could plausibly be done at NCAUR's newly
renovated pilot plant facility, says center director Peter B. Johnsen.
From among the "magnificent seven" microbes, one is a yet-unnamed
strain of a yeast that is new to science, according to NCAUR microbiologist
Cletus P. Kurtzman. In 3 years of field tests at a few locations, all these
microbes have shown promise, several reducing disease severity up to 80
percent. Because the microorganisms may reduce disease in different ways, they
might be applied in combinations.
Inasmuch as late-applied chemical fungicides could leave chemical residues on
wheat used for food, few have been registered for use during the critical time
of pathogen infection—wheat flowering through early kernel development. If
some microorganisms prove resistant to damage from a chemical fungicide, they
could be applied along with the fungicide. "That should reduce the amount
of chemical fungicide needed and may reduce the chance of the pathogen's
developing resistance to the fungicide," says Schisler.
"Considering the labor and logistics needed to prepare for field tests at
13 state agricultural experiment stations, we had to choose just one microbe to
prove the biological-control concept," says Schisler. The researchers
weighed their choices according to several considerations, one of which was the
microbes' resistance to registered and experimental fungicides. Other
considerations included how massively and quickly yeast cells reproduced in the
bioreactors, their ability to survive and remain healthy in storage, and how
effectively they worked after storage in arresting the growth of F.
graminearum.
Commercial and experimental fungicides, along with the yeast and a strain of
the bacterium Bacillus subtilis, are being compared in annual field
tests known as the Uniform Wheat Fungicide Trials. Research on the bacterium
was conducted at Cornell University. The trials, a cooperative project funded
by USDA and state agricultural experiment stations, will provide direct
comparisons of scab-control measures in various environments, from year to
year. The experiment stations include those in Arkansas, Indiana, Iowa,
Kentucky, Maryland, Michigan, Minnesota, Missouri, New York, North Dakota,
Ohio, South Dakota, and Virginia.
While the Uniform Wheat Fungicide Trials proceed, Schisler and his colleagues
continue to search for microbes with enhanced biological control potential,
attune their bioreactors to produce high yields of various microbial strains,
find ways to ensure the strains survive well in storage, and test those strains
in the field.
The NCAUR scientists' early laboratory and collaborative field research on
biological control of scab also provided impetus for international cooperation
in problem solving. Liubov V. Kolombet, a microbiologist and chief of the
Department of Antimicrobial Agents for Plant Protection at the State Research
Center for Applied Microbiology at Obelinsk, Russia, visited Schisler at NCAUR
for 3 weeks to formulate a proposal for a grant from the ARS-FSU (Former Soviet
Union) Science Cooperation Project. The research proposal involves strains of
Trichoderma fungi that have been researched at the Russian institution.
Someday these fungi may be applied as a seed coating to make plants better fit
to resist scab as they approach maturity.—By
Ben Hardin,
Agricultural Research Service Information Staff.
This research is part of Crop Protection and Quarantine, an ARS National
Program (#304) described on the World Wide Web at
http://www.nps.ars.usda.gov.
David A. Schisler and
others mentioned in this article are with the USDA-ARS
National Center for Agricultural
Utilization Research, Fermentation Biochemistry Research Unit, 1815 N.
University St., Peoria, IL 61604; phone (309) 681-6284, fax (309) 681-6427.
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"Yeast Debuts in Tests on Controlling Wheat
Scab" was published in the
June 2001
issue of Agricultural Research magazine.
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