microorganisms can suppress soilborne pathogens after many years of a crop monoculture (that is, without crop rotation). Until recently, US agriculture has not taken advantage of microorganisms to protect crops against harmful pathogens.

David Weller, R.James Cook, Jos Raaijmakers, and Linda S.Thomashow (CRGO/NRI funded scientists) have spent the last 2 decades studying the microbiologic basis of the decline of take-all disease after 12–15 years of wheat monoculture. Take-all is the most serious root disease of wheat worldwide because most of the world’s major wheat-growing areas, lacking economically suitable broad-leaf crops that could be grown in alternate years, use little or no crop rotation. Take-all is especially devastating where wheat is planted with reduced tilling to reduce soil erosion, and it has been known to wipe out entire fields.

Soil laden with some strains of root-associated Pseudomonas, including P. fluorescens and P. chlororaphis, appears to suppress the fungal pathogen. These scientists have shown that those bacteria produce natural antibiotics (mainly 2,4-diacetylphloroglucinol and phenazine-1-carboxylate) that stop the growth of the fungus. Their research has provided the first proof that the ability of soil microorganisms to produce antibiotics is critical to their survival and activity in soil and that antibiotic-producing soil microorganisms constitute one of nature’s most effective methods for management of plant diseases. In addition to the knowledge of how to manage the beneficial bacteria through the cropping system, these strains of Pseudomonas can be grown in industrial quantities in fermentors and applied as a biologically safe seed coating that prevents take-all disease in wheat.

Three patents have been issued, two more are pending, and two license agreements have been issued for use of specific strains in turf, as well as wheat.

In 1997, Weller, Thomashow, Cook, and Raaijmakers received the Ruth Allen Award; this is the highest award for research given by the American Phytopathological Society and recognizes contributions to science that have changed the direction of research.

CRGO and NRI Awards to Cook and colleagues:
  • 1978; Biological Stress on Plants; $120,000; 3 years.

  • 1981; Biological Stress on Plants; $60,000; 2 years.

  • 1986; Biological Stress on Plants; $100,000; 2 years.

  • 1989; Plant Pathology/Weed Science; $100,000; 2 years.

  • 1991; Plant Pathology/Weed Science; $120,000; 2 years.

  • 1991 (1993 renewal); Plant Pathology; $100,000; 2 years.

  • 1994; Soils and Soil Biology; $212,000; 3 years.

  • 1996; Plant Pathology; $ 116,041; 2 years.

  • 1994 (1997 renewal); Soils and Soil Biology; $255,000; 3 years.



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