Characterization of Plant Growth Promoting Rhizobacteria and Their Benefits on Soybean Growth

Background: Soybean is the most important legume in the world and its seeds contains 40% protein and 20% oil. In recent years, more attention has been paid to the use of plant growth-promoting (PGP) rhizobacteria as a biofertilizer alternative to chemical fertilizers, which may pose risks to the environment. The rhizobia inoculation of soybean is a sustainable practice to induce atmospheric nitrogen fixation and subsequently improve crop productivity and soil fertility. Methods: In this study, 19 indigenous rhizobia isolated from soybean were tested in vitro for their plant growth-promoting properties (PGPR), while genotypic characterization included sequencing of the 16S rRNA gene. Result: Morphological characterisation has shown that all of the isolates were rod-shaped gram negative bacteria. The sequencing has shown that 12 out of 19 isolates belong to the genus Pseudomonas, four of which belong to P. fluorescens species. Isolates which belong to the Pseudomonas genus have shown the highest ability of indole-3-acetic acid synthesis, phosphorous solubilization and along with isolates SGN6, SGN7 and SGS4 (Sphingomonas sanguinis) potassium solubilisation too. All the isolates from Pseudomonas genus as well as those belonging to B. japonicum species have shown the protease synthesis abilities while amylase synthesis abilities was observed only in the isolate SAK2 (P. chlororaphis). The most efficient strains in in vitro biological nitrogen fixation assay belong to Pseudomonas and Rhizobium genera. Most of the isolates were positive to the organic acid production while all of them have shown the ability of the exopolysaccharide production.