Abstract
Phosphate solubilizing microorganisms (PSMs) were isolated from rhizoplane, rhizosphere and non-rhizosphere of different leguminous plants. To isolate efficient phosphate solubilizers the rhizosphere and non-rhizosphere soil samples were enriched with different phosphate sources like tricalcium and rock phosphate. PSMs were detected in all the regions, but their number gradually decreased from rhizosphere, rhizoplane and non-rhizosphere soil. When compared to fungal population, bacterial population was more in number. Tephrosia purpurea recorded the highest bacterial population of 30.15 × 106 cfu/g, 50.51 × 106 cfu/g and 21.10 × 106 cfu/g in the rhizoplane, rhizosphere and non-rhizosphere regions respectively. In enrichment culture technique, highest phosphate solubilizing bacterial population was recorded in the rhizosphere soil of Clitoria ternatea (23 × 103 cfu/g) in tricalcium phosphate containing Pikovskaya’s (PVK) medium. In a plate assay method solubilization zone diameter produced by microorganisms was varied from 0.2 cm to 1.0 cm. The phosphate solubilization ability of the isolated microorganisms in a liquid PVK medium varied from 11.85 mg to 61.96 mg P2O5. The medium turned acidic during the incubation period. The pH varied among the organisms from the initial 6.5 to the final 3.2 during 15 days of incubation. Citric acid, fumaric acid, gluconic acid, glutaric acid, glyoxalic acid, ketobutyric acid, ketoglutaric acid, malic acid, malonic acid, succinic acid and tartaric acid are produced by the isolated PSMs. Seed or soil inoculation with phosphate solubilizing bacteria (PSB) is known to improve solubilization of fixed and applied phosphates in soil bring about higher crop yield. The PSM are effective as biofertilizers in enhancing crop yields in phosphate deficient soils. They are environmentally friendly and supply phosphate to plants in a sustainable manner.
Highlights
Phosphorus (P) is a one of the major plant growth-limiting nutrients it is abundant in soils in both inorganic and organic forms
The total number of bacterial and fungal colonies varied in the three different regions; Phosphate solubilizing microorganisms (PSMs) were detected in all the regions, but their number gradually decreased from rhizosphere, rhizoplane and nonrhizosphere soil
When compared to fungal population, bacterial population was greater in number
Summary
Phosphorus (P) is a one of the major plant growth-limiting nutrients it is abundant in soils in both inorganic and organic forms. Soil microorganisms play a significant role in mobilizing P for plants by bringing about changes in pH in rhizosphere soil and by producing chelating substances, which lead to solubilization of phosphates [1]. These microbes are known as phosphate solubilizers consisting predominately of fungal, bacterial and Actinomycetes species collectively called the phosphate solubilizing microorganisms (PSM) [2]. Bacteria and fungi, growing in the root region of plants play an important role in the supply of P in rhizosphere region.
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