Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/17/1995
Publication Date: N/A
Interpretive Summary: Root pathogens are major yield-limiting factors in the production of food and fiber crops. Take-all, caused by the fungus Gaeumannomyces graminis var. tritici (Ggt), is the most important root disease of wheat. Interest in the use of microorganisms to suppress root pathogens has been stimulated by trends in agriculture toward greater sustainability and public concerns about hazards associated with the use of chemical pesticides. Take-all can be suppressed by a variety of soil microorganisms including Gaeumannomyces graminis var. graminis, (Ggg) which is a pathogen of rice but not of wheat. Ggg colonizes the roots of wheat and barley without causing damage. Ggg provides biocontrol by inducing natural host defenses in wheat and barley and by competition directly with Ggt for substrates and favored sites on roots. The purpose of this research was to study the biocontrol activity of Ggg against take-all of wheat and to determine its compatibility with Pseudomonas bacteria that are also known to have biocontrol activity. It was hypothesized that combining these organisms with different biocontrol mechanisms would result in enhanced take-all suppression. Combining Ggg with the Pseudomonas bacteria resulted in improved biocontrol of take-all in growth chamber experiments. However, in field trials, combining the fungus with the bacteria did not improve biocontrol of take-all as compared to Ggg and the Pseudomonas bacteria used alone.
Technical Abstract: Gaeumannomyces graminis var. graminis, originally isolated from rice, suppressed take-all of wheat casued by Gaeumannymyces graminis var. tritici in growth chamber studies when appled to the soil. Furthermore, combination treatments consisting of G.g. var. graminis applied to the soil and fluorescent Pseudomonas strains applied to the seed, either 30-84, Q29z-80, Q69c-80, or a mixture of strains (Q2-87 plus Q1c-80 plus Q8d-80 plus Q69c-80), were significantly more suppressive of take-all than either treatment used alone. In a winter wheat field trial at Pullman, Wash., G.g. var graminis applied to the seed furrow significantly reduced crown root infection by G.g. tritici and the strain mixture reduced seminal root infection suggesting differential protection at various stages of disease development. However, in contrast to growth chamber studies, the combination of G.g. var. graminis and the strain mixture did not enhance the take-all suppression in the field compared with the same treatments used alone.