Isolation and characterization of plant associated Rhizobacteria for plant growth promoting traits

The use of plant growth promoting rhizobacteria (PGPR) in sustainable and eco-friendly management of plant growth promoting is gaining importance over the previous decades around the world. In the current research work, we have isolated and characterized 32 rhizobacterial isolates from five different plant species. All the 32 rhizobacterial isolates showed at least one of the three major functionalities; viz. phosphorus solubilization, indole acetic acid production and nitrogen fixation; considered for selection of PGPR when tested in-vitro. Among the 32 isolates, 15 produced a clear halo zone surrounding their colonies indicating phosphate solubilization with variable intensities. Six bacterial isolates showed high phosphate solubilization index (PSI) and also proved to be efficient phosphorus solubilizers. The bacterial isolate MQ2 solubilized maximum (0.697 µg/mL) phosphorus in liquid medium, followed by MQ3 and MQ1. Ten of the bacterial isolates were able to synthesize indole-3-acetic acid (IAA) in L-tryptophan supplemented media at varying capacity. The isolate OSn8 produced the highest amount (6.204 µg/mL) of IAA followed by MQ5 and OSbr6, while the lowest amount of IAA (1.268 µg/mL) was produced by MQ1. All the isolated bacteria were tested positive for putative nitrogen-fixing ability with variation among the isolates as indicated by their growth in N-free medium. Considering all three tested functionalities, the isolate MQ1 proved to be the best candidate for potential biofertilizer development. A consortium of isolated rhizobacteria comprising the best isolates from each category could be constructed to provide the best benefit to crops for maintaining yield and quality while decreasing agrochemical inputs.