Characterization of phosphate-solubilizing microorganisms from salt-affected soils of India and their effect on growth of sorghum plants [Sorghum bicolor (L.) Moench]

Indigenous phosphate-solubilizing microorganisms (PSM) were studied in the rhizosphere and non-rhizosphere of salt-affected soils. A total of 23 phosphate-solubilizing bacteria (PSB) and 35 phosphate-solubilizing fungi (PSF) were isolated from 19 samples collected from different locations in Karnataka and Madhya Pradesh of India. The counts of PSB and PSF showed large variations. The bacterial isolates were identified using BIOLOG as belonging to Pseudomonas, Xanthomonas, Bacillus, Aerococcus, Alteromonas, Erwinia and Enterobacter. Fungal isolates were identified as Aspergillus and Penicillium based on colony morphology, microscopic observations and BIOLOG. All the PSB and PSF isolates were able to produce both indole acetic acid (IAA) and gibberellic acid (GA). Bacterial isolates produced IAA in the range of 0.74 to 9.53 μg 25 ml−1, and GA ranged from 2.08 to 12.55 μg 25 ml−1. The amount of IAA produced by the PSF isolates ranged from 2.33 to 8.69 μg 25 ml−1, and GA ranged from 3.44 to 14.80 μg 25 ml−1. Fungal isolates were superior to bacterial isolates in terms of P solubilization as measured by release of inorganic phosphate (Pi) from tricalcium phosphate, increase in stem girth, root length, root dry matter and total dry matter of sorghum plants.