Use of a Consortium of Agronomically Important Microorganisms for Growing Soybean (Glycine max (L.) Merr.)

Abstract

Aims: This study aimed to create a consortium of agronomically important microorganisms based on local strains of rhizobia and phosphate-solubilizing bacteria that could increase the nitrogen and phosphorus nutrition of soybean, thereby increasing its productivity in Kazakhstan. Background: The use of agronomically important microorganisms that simultaneously possess several useful properties for growing plants is a priority for the sustainable development of organic agriculture. Objective: The objectives of the study were to isolate and functionally characterize rhizobia from soybean nodules (Glycine max (L.) Merr.) and phosphate-solubilizing bacteria from rhizosphere soybean. Methods: In this study, local rhizobia and phosphate-solubilizing bacteria adapted to the soil and climatic conditions of Kazakhstan were isolated from the nodules and rhizosphere of soybean. The nitrogenase activity of rhizobia was determined by the acetylene reduction assay. The biocompatibility of consortium strains was determined by the perpendicular streak technique. The plant growth-promoting activity, nitrogenase, phosphate-solubilizing activity, and nodulation of isolated bacteria were studied, and the four most active strains were selected. Identification of these strains was carried out by sequencing the 16S rRNA. Consortia of agronomically important microorganisms were created based on active strains of rhizobia and phosphate-solubilizing bacteria. Results: The sequencing of 16S rRNA of the selected strains showed that rhizobia belonged to the genus Rhizobium and the phosphate-solubilizing to the genera Pseudomonas and Enterobacter. The results showed that seeds inoculation by consortia had a highly stimulating effect on soybean plants' growth and significantly increased the stem height (1.8-2.0 times), root length (2.3-2.7 times), and the number of nodules (2.7-3.2 times) compared to the control without inoculation. Besides, these consortia induced a significant increase in the number of nodules on soybean roots and their nitrogen fixation, an increase in phosphorus absorption, and an increase in protein in soybean plants compared to the control. According to these results, consortium No. 21 was selected as the most effective one. The consortium included strains of rhizobia Rhizobium lupini RH-7 and phosphate-solubilizing bacteria Pseudomonas koreensis FT-4. Conclusion: A consortium of agronomically important microorganisms based on local strains of bacteria adapted to the soil and climatic conditions and not competing with microbes of the rhizosphere was created in our study. The use of a consortium based on local strains will help avoid competition with the indigenous populations of rhizosphere bacteria, and it can be used to grow an economically important crop, such as soybean.