Taking Wheat Away from Take-All
By Sharon Durham
October 18, 2000
Agricultural Research Service scientists
have screened hundreds of different bacterial strains to find potential natural
biological controls for take-all, a fungal disease that demolishes wheat
harvests around the world. The fungus Gaeumannomyces graminis var.
tritici (Ggt) spreads take-all, which causes wheat roots to turn black and
die. The disease can reduce yields by 50 percent or more, costing U.S. wheat
growers millions of dollars in bad year.
Daniel Roberts, a microbiologist in the
ARS Biocontrol of Plant
Disease Laboratory in Beltsville, Md.; Jeff Buyer, a chemist in the
ARS Soil Microbial
Systems Laboratory in Beltsville, and collaborators at
Virginia Polytechnic Institute and State
University screened large numbers of diverse bacteria for their ability to
suppress Ggt. Searching soft red winter wheat fields in Virginia, Roberts
concentrated on checking out bacteria in the rhizosphere, the zone immediately
surrounding plant roots containing soil and an abundance of microorganisms.
To screen for potentially beneficial strains, Roberts and his team
used a commercially available analytical system that identifies fatty acid
profiles of bacteria. These fatty acid profiles are unique for each strain,
allowing the scientists to sift through isolates from many soil samples and
identify the bacteria by their fatty acid signatures.
Roberts found several candidate bacterial strains that were worthy of
further testing. He then applied these strains to wheat seeds before planting
them in test plots. Low levels of Ggt were also added to the seeds to ensure
the presence of the disease.
After three years of testing and approximately 400 candidates, Roberts and
his colleagues found four bacterial strains that show promise as take-all
biocontrols. Scientists will test these four bacterial strains separately and
in combination with commonly used wheat pesticides this year in field trials.
If these trials find that one or more of the bacterial strains are
effective, then work will begin to develop a formulation of beneficial bacteria
that can be integrated into pest management strategies.
ARS is the chief scientific research agency of the
U.S. Department of Agriculture.
Scientific contact: Daniel Roberts, ARS Biocontrol of Plant Diseases
Laboratory, Beltsville, Md.; phone (301) 504-5680; fax (301) 504-5968;