It is known that the ratio of the main groups of microorganisms in the microbiocenosis form the biological fertility of the soil. In this regard, it is necessary to take into account the influence of biologically active substances, including nanoparticles and their derivatives, used in crop production, on the composition of soil microbiota and its biodiversity. The aim of this study was to investigate the effect of Galega orientalis plants inoculation with phytopathogenic microorganisms and foliar treatment of plants with nanochelates on the total amount of microbial groups in rhizosphere of Galega orientalis. Methods. Acholeplasma laidlawii var. granulum 118 UCM BM–34 was cultivated in the liquid nutrient medium CM IMV-72 (pH 7.8) in thermostat at 32°C for 72 hours. Pseudomonas syringae pv. atrofaciens D13 was cultivated on potato agar in thermostat at 26–28°C. For artificial infection a bacterial suspension with a concentration of 1×109 CFU/mL according to the turbidity standard was prepared. Galega orientalis plants were inoculated with phytopathogenic strains of microorganisms by subepidermal injection into the stem. The total count of microbial groups in the samples was performed by the method of plating on selective media, the result was expressed in colony-forming units (CFU). For statistical processing of data, calculations of the arithmetic mean and its standard error were performed. Results. It was found that the total amount of microorganisms, the number of actinomycetes and oligotrophic microorganisms increased and the number of micromycetes decreased in the rhizosphere of Galega orientalis plants infected with phytoplasma. In contrast to phytoplasma infected plants, the number of aerobic nitrogenfixing bacteria in the rhizosphere increased in plants infected with P. syringae pv. atrofaciens D13. Foliar treatment of Galega orientalis plants with nanochelate solutions had varying influence on the composition of microbial groups. The total amount of aerobic nitrogen-fixing bacteria increased after foliar treatment with nanochelates in the next order: V˃Ge˃Se, and the total amount of actinomycetes increased after foliar treatment in the next order: Se˃V˃Ge. The total amount of micromycetes increased in the rhizosphere of Galega orientalis after foliar treatment with Ge and Se nanochelates. It should be noted that the most significant increase in the number of oligotrophic microorganisms was observed in the rhizosphere of plants after I-Se foliar treatment. Conclusions. The number of actinomycetes, micromycetes and oligotrophic microorganisms in the rhizosphere of Galega orientalis plants infected with A. laidlawii and P. syringae increased compared to control plants; this process was associated with changes in the chemical composition of root secretions, probably due to reducing of carbohydrates and the presence of stress signal molecules. Plants infection with these pathogens had different effect on the total amount of aerobic nitrogen-fixing bacteria, the number of which increased in the rhizosphere after infection with P. syringae and decreased after infection with A. laidlawii, which may be due to the different chemical composition of the root secretions. Foliar treatment with Se, Ge and V nanochelates had the most favorable influence on the soil microbiota, causing an increase in the total amount of microbial groups, including species capable of disease development inhibiting and participating in the nutrient cycle (aerobic nitrogen-fixing bacteria, actinomycetes, micromycetes). The foliar treatment of plants with I-Se nanochelates can be considered as conditionally favorable due to a significant increase in the number of oligotrophic microorganisms, which indicates the depletion of readily available nutrients in the soil. However, the improvement of root system growth at I-Se foliar treatment of plants affected by both phytoplasma and bacterial pathogen may be a sign of stimulation of the absorptive capacity of roots, which requires further research.
