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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, 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. [ABSTRACT FROM AUTHOR]

Breeding of wheat cultivar resistant against root diseases is a difficult problem because the lack of evidence about nature of pathogenicity of soil-borne fungi -causal agents of these diseases and their interaction with host plant. The aim of this research was to investigate the character of pathogenicity of Bipolaris sorokiniana, Fusarium spp. и Oculimacula spp. - causal agents of common root rot, Fusarium root rot and eyespot on wheat seedlings under the artificial inoculation with isolates B. sorokiniana, F. oxysporum, F. culmorum, O. acuformis and O. yallundae. It has been revealed that there is significant difference between isolates B. sorokiniana, F. culmorum and F. oxysporum in pathogenicity, which was confirmed by the assessment of root rot severity on inoculated seedlings. Under the artificial inoculation of wheat seedlings with isolates O. acuformis and O. yallundae the severity of eyespot depends significantly on wheat cultivar characteristics. Based on results of our experiments we also suggested the virulence characteristic in B. sorokiniana isolates. Thus, it has been confirmed the specificity of interaction the soil-borne fungi with plant host in every particular pathosystem, that should be considered in breeding programs for resistance against root and stem-base diseases. [ABSTRACT FROM AUTHOR]