Density dynamics of the entomopathogenic fungus, Beauveria bassiana Vuillemin (Deuteromycotina: Hyphomycetes) introduced into forest soil, and its influence on other soil microorganisms

Abstract

Beauveria bassiana conidia were mixed into the forest soil, and the density dynamics of soil microorganisms were investigated using selective media to clarify the impact of B. bassiana application on them. The density of bacteria was between 1×106 and 108 CFU/g, and that of actinomycetes was around 1×106 to 107 CFU/g regardless of the addition of B. bassiana. Densities of general fungi and of B. bassiana in the non-treatment plot were always approximately 1×105 CFU/g and 1×102 CFU/g, respectively. On the other hand, densities of both general fungi and B. bassiana in the treatment plot increased to 3 to 5×107 CFU/g immediately after the mixing of B. bassiana. Densities gradually decreased to 1/10 the density after 12 months. Microscopic observations revealed that B. bassiana conidia do not germinate in non-sterilized soil, but they do germinate in sterilized soil. Densities of fungi other than B. bassiana could not be measured in the treatment plot. However, they were not thought to be affected by mixing of B. bassiana, because the metabolism of B. bassiana seemed to be very inert.