Isolates of Gaeumannomyces spp. obtained from diseased roots of winter wheat showing take-all symptoms were characterized by pathogenicity. All isolates were more pathogenic on wheat and barley than on oat, and were identified as Gaeumannomyces tritici. Most isolates of G. tritici were characterized as middle pathogenic, the pathogenicity of one isolate was higher than those of others, and two isolates showed the lowest pathogenicity. In growth chamber assay, the effect of two Bacillus strains,

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... B. subtilis 16 and B. pumilus 11, on take-all of wheat was studied. Pathogen inoculation was made by isolates of G. tritici of different pathogenicity. It was found that effective biological control depends on take-all severity, which, in turn, co-ordinates with the pathogenicity of fungal isolate. Applying the bacterial cells into the plant growth substrate stimulated the seedling growth when artificial inoculation was performed with a middle pathogenic isolate of G. tritici, and the disease severity was middle. There was no growth promotion by bacterial inoculant at slight disease severity. No stimulating effect was also observed at the high disease severity, where pathogen inoculation was performed with a highly pathogenic isolate of G. tritici.