STUDY OF THE ABILITY OF RHIZOSPHERE MICROORGANISMS TO PRODUCE IAA AND THEIR INFLUENCE ON PLANT GROWTH

Abstract

A primary screening was conducted to assess the ability of rhizosphere microorganisms from cultivated and wild plants of arid ecosystems in the Astrakhan region to produce indoleacetic acid (IAA) and exhibit phytotoxic properties. The amount of synthesised IAA was determined using a photometric method, and the phytotoxicity of microbial culture liquid was evaluated on seeds of red round radish Raphanus sativus L. convar. radicula. It was found that all isolates had the ability for tryptophan-induced IAA synthesis. Out of the 50 examined isolates, 19 synthesised IAA at levels comparable to industrial producers 80 µg/ml and higher. The evaluation of the influence of microbial culture liquid on the growth and development of radish seeds revealed complete inhibition of the root system and seedling effect for all isolates. Among the examined isolates, 16 completely suppressed the growth of test plant seeds. Seed germination using the suspension of other isolates ranged from 7.1% to 63.3%. The experiment established that phytotoxic effects also increased with an increase in the amount of IAA synthesised by isolates. The influence of exogenous auxin on plant development can have positive and negative effects. The optimal concentration range of IAA for a specific plant can be extremely narrow, and any deviation from this concentration can lead to inhibitory effects. Therefore, further research is needed to explore the biotechnological potential of isolated strains with increased IAA production as industrial producers of this substance or as the basis for a biological preparation for plant growth stimulation.