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Primary evaluation of newly isolated strains of phosphate-mobilizing bacteria

Isolation and screening of strains with increased phosphate-dissolving activity are necessary stages of research on the intensification of phosphorus nutrition of plants by pre-sowing inoculation of seeds with effective microorganisms. The purpose of the research was to study the phosphate-dissolving activity of newly isolated bacterial strains and their effect on the sowing qualities of winter wheat seeds. Phosphate-mobilizing bacteria were isolated in 2014–2019 from the сhernozem southern sampled in the fields of the Order of the Red Banner of Labour Agro-Industrial College – structural unit of V.I. Vernadsky Crimean Federal University. Laboratory studies were carried out in 2019–2020 in the Department of Agricultural Microbiology of the Research Institute of Agriculture of Crimea. The isolation of strains of soil phosphate-mobilizing bacteria was carried out based on the appearance of a clear zone around the colonies on agarized glucose-aspartic (GA) medium supplemented with Ca3(PO4)2. The coefficient of specific phosphate-dissolving activity (Kr) of the strains was calculated according to the method of I. M. Malinovskaya. The quantitative assessment of the phosphate-dissolving activity of bacteria in a liquid medium (P2O5 content) was determined by the colorimetric method. High Kr is typical for the predominant part of the studied strains (22 or 81.5 %). The highest Kr value (10) was noted for strain 0613. Twelve (44 %) strains demonstrated the highest ability to transform Ca3(PO4)2 into a soluble form. The maximum content of P2O5 (212 mg/l) was observed in the culture fluid of strain 1702. When winter wheat seeds were inoculated with strains 0890 and 1702, germination increased by 8–9 %. The same was with germination energy; it also increased compared to control (water) by 2.5 and 7.5 %, respectively. The use of strain 1303 contributed to a significant increase in the energy and germination rate of seeds: by 34.5, 6 and 5.6 %, respectively, compared to control. The strains provided a significant increase in the weight of seedlings compared to control: by 29 % – the reference strain; by 32, 38 and 29 % – newly isolated 0735, 1204, 1701, respectively.