Characterization and performance evaluation of plant growth promoting bacteria in tomato rhizosphere

An acute and compelling need to replace chemical fertilizers has shifted our focus towards plant growth-promoting rhizobacteria (PGPR) that rapidly colonize the rhizosphere. In the present investigation, two isolates from tomato rhizosphere, TS4 and TS6, were screened for various PGPR properties. Both isolates expressed different properties such as enzyme production and hydrogen sulfide (H2S) production. Production of Indole-3-Acetic Acid (IAA) was 13.33 μg mL−1 for both TS4 and TS6. Ammonia excretion was 75.0 μg mL−1 for TS4 and 82.5 μg mL−1 for TS6. Both isolates tolerated salt stress up to 10% sodium chloride (NaCl), drought stress tolerated by isolate TS4 was up to -0.30 MPa and TS6 survived up to -0.49 MPa osmotic pressure. To assess the colonization potential of the isolates, their biofilm potential and chemotactic behavior towards the tomato root exudates were studied. Colonization of the tomato rhizosphere by TS4 and TS6 was observed quantitatively and found that root tips were more profusely colonized as compared to the root base. Nethouse studies to test their influence on tomato revealed a positive influence in some plant aspects. All the results led to the conclusion that isolates TS6 identified as Micrococcus luteus and TS4 belonging to genera Lactobacillus were efficient PGPR. This paper highlights the efficacy of PGPR as a component of sustainable agriculture for improved productivity. However, the need of risk assessment and rigorous surveillance of bacteria before developing them as a bioformulation is also emphasized.