Plant Growth-Promoting Activities and Molecular Characterization of Rhizobacterial Strains Isolated From Medicinal and Aromatic Plants

Rhizosphere bacteria are known to influence plant growth by direct and indirect mechanisms.Development of an effective plant growth promoting rhizobacteria (PGPR) inoculant necessitates the presence of a diverse set of traits that can help its colonization of the rhizosphere and survival under varying environmental conditions.In the present study, a total of 219 bacterial strains isolated from the rhizosphere of different medicinal and aromatic plants collected from different locations of Andhra Pradesh (India) were initially screened for their PGP activities.From the 219 isolates four bacterial strains were selected and tested for in vitro specific plant growth promotion activities such as ammonia production, IAA production, phosphate solubilization, HCN production and antifungal activity.These four isolates showed maximum plant growth promoting activities and further they were identified on the basis of colony morphology, gram staining and biochemical tests.These PGPR isolates were characterized through 16S rRNA gene sequencing which led to their identification as Pantoea sp.(Cf 7), Bacillus sp.(Cf 60) and Pseudomonas sp.(Te1, Av 30) respectively.Seed germination test was conducted by employing these strains under laboratory conditions on sorghum, maize and green gram seeds to investigate the effect of PGPR on the growth of seedlings.These PGPR isolates induced production of plant growth hormones (indole acetic acid), phosphate solubilization and ammonia production resulting in enhanced plant growth.Most of the isolates resulted in a significant increase in % of seed germination, shoot length, root length and vigor index of sorghum, maize and green gram seedlings.Therefore, the present study suggests that these PGPR isolates (Cf 7, Cf 60, Te1, Av 30) may be used as biofertilizers to enhance the growth and productivity of commercially important medicinal and aromatic plants.