No abstract

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.

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.

The new taxonomic marker (hin-region) has been proposed, which gives possibility for Rhizobium bacteria study on “species — group of strains” level. Using this marker the groups of Rhizobium strains were determined, which could not be distinguished with other methods, and these results correlated with evolutionary similarity of the bacteria. The developed approach for creating marker systems allows to carry out effective inventory of inter- and intraspecies genetic diversity of nodulating bacteria and to evaluate perspectives of their use in agriculture. The proposed marker system was used for description of Rhizobium bacteria samples isolated from various ecological-geographical regions of Ukraine.

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.