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, andcollaborators 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 teamused 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; robertsd@ba.ars.usda.gov.