ISOLATES FROM THE RHIZOSPHERE AND SUNFLOWER PHYLLOPLANES, PRODUCERS OF PHYTOHORMONES AS POTENTIAL BIOAGENTS-STIMULATORS OF PLANT GROWTH

In the context of global environmental challenges, there is an increasing need to modernize agriculture by developing and disseminating environmentally friendly bacterial inoculants capable of replacing chemical fertilizers and pesticides, which is especially important for the sustainable development of agriculture. The studies were conducted to find microorganisms-producers of phytohormones to stimulate plant growth and to form a biologically active consortium. The work was carried out in laboratory conditions with 17 isolates of microorganisms, capable of synthesizing auxins, in particular, indole-3-acetic acid, isolated from the rhizosphere and phylloplane of sunflower. Screening of the biosynthesis of this acid by the studied isolates in a plate test on an agar medium with Salkovskiy’s reagent revealed a qualitative positive reaction and established the concentrations of indole-3-acetic acid in the assigned isolates. As a result of studying the phenotypic characteristics and molecular genetic analysis of the 16S rRNA gene sequences, the species affiliation of the isolated microorganisms was determined. The three most active isolates, capable of producing the phytohormone, belong to the Pseudomonas genus and were identified to the species level as Pseudomonas poae, Pseudomonas frederiksbergensis and Pseudomonas brassicacearum. The synthesis of indole-3-acetic acid by these isolates is 93.0±0.4 μg/ml; 69.6±2.0 μg/ml and 74.2±2.5 μg/ml, respectively. KPD77 isolate, identified as Arthrobacter oryzae, demonstrated the level of synthesis of indole-3-acetic acid equal to 86.1±2.8 μg/ml. The ability of microorganisms of this species to synthesize such a phytohormone was established for the first time. Based on the data obtained, five promising isolates extracted from the rhizosphere and sunflower of were selected to form a consortium of microorganisms designed to stimulate plant growth.