Associative microorganisms live in the zone of direct influence of plants namely in the soil, which is in close contact with the roots. They form complex communities on the roots of plants in terms of taxonomic composition and structural and functional o8rganization, which have polyfunctional effect on plants. Rhizosphere biotechnologies with the use of associative bacteria to a specific plant species allow increasing their productivity and quality, which contributes to the stability of agroecosystems. Therefore, the main goal of the current study was to isolate associative to Triticum aestivum L. bacteria from the southern chernozem (Haplic Chernozems), which was sampled in the steppe zone of the Crimea. The methodical approach was used to select associative microorganisms for a specific plant species. The number of microorganisms of the main ecological-trophic groups for three varieties T. aestivum were determined. The maximum number of rhizosphere microorganisms was identified for the Ermak variety, as well as the number of morphotypes isolated from the apical part of the root. As a result of the research, six strains of associative bacteria were obtained. They increased the seed quality of the studied varieties by 5% and the biomass of the seedlings by 80%. Identification by the 16S rRNA gene showed their belonging to different bacterial genera. Thus, the quantitative composition of the chernozem southern of the rhizosphere of three varieties of T. aestivum was determined. Five strains of associative bacteria promising for further biotechnology of the agrocenosis rhizosphere were isolated.

The taxonomic structure of the microbiome of southern chernozem compared to virgin soil was studied in the stationary experiment on the use of microbial preparations in the conditions of traditional for the steppe part of the Crimea and each culture of the five-field crop rotation of the farming system and no-till. Among 823 genera it was revealed 7 dominant ones: Candidatus Nitrososphaera, Rubrobacter, Flavisolibacter, Segetibacter, Bacillus, Balneimonas, Skermanella. The low level of cellulose-decomposing bacteria of the genus Cellulomonas was remarked in southern chernozem. The highest proportion of the representatives of this genus was observed in virgin soil (0.55 %), while the farming systems contributed to its decline in 1.3-1.6 times. Microorganisms of the genera Erwinia and Xanthomonas with phytopathogenic properties were found with a minimum proportion in communities from 0.003 % to 0.014 % and 0 – 0.005%, respectively. The complex metagenomic analysis of the taxonomic structure of the soil microbiome allowed us to establish that the use of microbial preparations reduces the negative impact of the no-till farming system on the microbiocenosis of southern chernozem and improves its environmental feasibility in the Crimean steppe.

Agricultural technologies aimed at reducing the tillage can be adopted as safer farming methods to preserve and improve the diversity of soil microbial communities. The area under the promising resource-saving no-till system (direct sowing) is increase in the conditions of the Steppe annually. The use of herbicides in such a farming system causes a negative effect on the soil biocenosis. But the introduction of agronomically useful microorganisms into the rhizosphere are increasing the resistance of plants against stress factors, their yields and product quality, and preserving soil fertility. The objective of this research was to assess the state of microbiocenosis of southern chernozem under the influence of no-till system and a complex of microbial preparations. The influence of direct sowing and microbial preparations on the state of microbocenosis of southern chernozem was established. The number of cellulolytic microorganisms increased under the influence of farming systems in comparison with the virgin soil. The use of microbial preparations contributed to an increase in the number of microorganisms of ecological and trophic groups and the representation of the majority of phyla, which also depended on the system of agriculture. A decrease in the representation of Acidobacteria and Verrucomicrobia and an increase in Firmicutes and Proteobacteria were observed in comparison with virgin soil.

Microbial preparations improve mineral nutrition of plants, protect against phytopathogens, and increase their resistance to stress factors. The aim of our research is to study the effect of microbial preparations on the biological activity of rhizosphere and the productivity of oil flax under no-till in the Crimean Steppe. Microbiological analysis of the rhizosphere of oil flax showed that there is a tendency to increase the number of microorganisms of various ecological and trophic groups both under the conditions of the conventional farming system (CFS) and no-till when seeds are inoculated with a complex of microbial preparations (CMP). Under CFS, the number of microorganisms using mineral forms of nitrogen as nutrition increased by 28 %; pedotrophs – by 37 %; ammonifiers and oligotrophs increased under both farming systems. The total number of nitrogen fixers increased by 29 % under CFS as a result of biological preparations use, while under no-till there was only a trend towards increasing the amount of azotobacter. The number of actinomycetes increased under the influence of CMP by 50% under direct sowing; micromycetes decreased under both farming systems. The number of cellulose-degrading microorganisms increased by 18 and 27 % under no- till and CFS, respectively. The yield of oilseed flax under no-till was 0.11 t/ha (12.9 %) higher than under conventional farming system. On average, over three years (2017-2019), an increase in yield amounted to 0.12 t/ha (19%) due to the use of microbial preparations.

Allium cepa L. is one of the main vegetable crops. It is actively used in food industry and medicine. The biochemical composition of plants, both bulbs and green leaves, in different periods of growth changes depending on the variety, environmental and agrotechnical conditions of plant cultivation. Representatives of the genus Allium are highly sensitive to the presence of arbuscular mycorrhiza (AM) in soil due to root development features. The aim of our work was to identify effective associations of AM fungi to increase the productivity and quality of onions in the conditions of southern chernozem. Pot and field experiments were carried out with associations of AM fungi and onion varieties from the collection of the Research Institute of Agriculture of Crimea. The initial assessment of the AM fungi collection was conducted in the pot with a sterile substrate under artificial lighting conditions according to the intensity of mycorrhizal colonization and the accumulation of phytomass of the storage plant. Field studies were carried out on southern carbonate chernozem in 2019. It is established that the AM fungi association M9 significantly exceeds the referent in the arbuscules abundance by 13.3 %. Association 1–16 showed the most considerable abundance of vesicles, which was 11.1–13.3 % higher than other variants of this experiment. The dry mass of onion shoots had a significant increase of 11.719.7 mg per plant (38.865.8 %) from inoculation by associations AM S1-4, 1-16 and M9. The positive effect of the AM fungi association 1-16 on the accumulation of phytomass in the onset phase of bulb formation and onion productivity of the onion variety Yaltinskiy plus and line 11A with an increase by 0.690.8 g / plant (31.351.7 %) and 1.11.3 t / ha (14.114.9 %), respectively, and an increase in the content of ascorbic acid by 18.524.4 % to the variant without treatment are shown.