Evaluation of plant growth promoting (PGP) efficacy of rhizospheric Pseudomonas strains

Plant growth promoting (PGP) potential of Pseudomonas species was evaluated from the normal and replant rhizospheric soils of apple orchards of district Shimla, HP. Total of twelve isolates were tested for multifarious PGP traits viz phosphate solubilization, production of plant growth regulators, antifungal metabolites and siderophores. The strains were further studied for their ability to produce plant growth promoting activities such as plant growth hormones production viz auxins, gibberellins and cytokinins, phosphate solubilizing activity, siderophore activity, protease enzyme activity, ammonia and HCN production. Auxins, gibberellins and cytokinins produced by isolates were in the range of 10-98, 35-105 and 19-82 ig/ml respectively. Pseudomonas isolates showed production of phosphate solubilizing activity in the range of 10 to 84 ig/ml and 15-48 mm in plate assay, siderophore production in the range of 14-28 mm in plate assay and 11.64-53.18 per cent SU in liquid assay. All twelve strains of Pseudomonas were also evaluated for their antifungal activity against plant pathogenic fungi. Maximum inhibition was recorded in Dematophora necatrix (50-60%) followed by Pythium ultimum (30-40%), Phytopthora cactorum and Fusarium cactorum by all Pseudomonas strains. The results suggested that all the isolates possessed multiple PGP traits thus can be further explored for their efficacy as effective PGPR (plant growth promoting rhizobacteria).