Phosphate solubilization activity of rhizobia native to Iranian soils
Agricultural soils in Iran are predominantly calcareous with very low plant available phosphorus (P) content. In addition to their beneficial N2-fixing activity with legumes, rhizobia can improve plant P nutrition by mobilizing inorganic and organic P. Isolates from different cross-inoculation groups of rhizobia, obtained from Iranian soils were tested for their ability to dissolve inorganic and organic phosphate. From a total of 446 rhizobial isolates tested for P solubilization by the formation of visible dissolution halos on agar plates, 198 (44%) and 341(76%) of the isolates, solubilized Ca3(PO4)2 (TCP) and inositol hexaphosphate (IHP), respectively. In the liquid Sperber TCP medium, phosphate-solubilizing bacteria (Bacillus sp. and Pseudomonas fluorescens) used as positive controls released an average of 268.6 mg L−1 of P after 360 h incubation. This amount was significantly (P < 0.05) higher than those observed with all rhizobia tested. The group of Rhizobium leguminosarum bv. viciae mobilized in liquid TCP Sperber medium significantly (P < 0.05) more P (197.1 mg L−1 in 360 h) than other rhizobia tested,. This group also showed the highest dissolution halo on the TCP solid Sperber medium. The release of soluble P was significantly correlated with a drop in the pH of the culture filtrates indicating the importance of acid production in the mobilization process. None of the 70 bradyrhizobial isolates tested was able to solubilize TCP. These results indicate that many rhizobia isolated from soils in Iran are able to mobilize P from organic and inorganic sources and this beneficial effect should be tested with crops grown in Iran.
Key wordscalcium phosphate legumes inositol hexaphosphate PGPR pH Rhizobium
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- Goldstein A H 1986 Bacterial solubilization of mineral phosphates: historical perspectives and future prospects. Am. J. Altern. Agric. 1, 51–57.Google Scholar
- Gupta R, Singal R, Shankar A, Kuhad R C and Saxena R K 1994 A modified plate assay for screening phosphate solubilizing microorganisms. J. Gen. Appl. Microbiol. 40, 255–260.Google Scholar
- Halder A K and Chakrabartty P K 1993 Solubilization of inorganic phosphate by Rhizobium. Folia Microbiol. 38, 325–330.Google Scholar
- Olsen S R and Sommers L E 1982 Phosphorus. In Methods of Soil Analysis, Part 2-chemical and Microbiological Properties, 2nd edn., Ed. Page AL. Am Soc. Agron. and Soil Sci. Soc. A. Madison, Wisconsin, USA.Google Scholar
- Richardson A E 2001 Prospects for using soil microorganisms to improve the acquisition of phosphorus by plants. Aust. J. Plant Physiol. 28, 897–906.Google Scholar
- SAS, Institute Inc 1990 SAS procedure guide version 6 edn. SAS Institute Inc Cary, NC, 705 p.Google Scholar
- Silva Filho G N and Vidor C 2000 Phosphate solubilization by microorganisms in the presence of different carbon sources. R. Bras. Ci. Solo. 24, 311–319.Google Scholar
- Somasegaran P and Hoben H J 1994 Handbook for Rhizobia — Methods in Legume-Rhizobium Technology. Springer-Verlag, New York.Google Scholar
- Vincent J M 1970 A Manual for the Practical Study of Root Nodule Bacteria. IBP handbook 15 Blackwell Scientific Publications, Oxford.Google Scholar
- Yanni Y G, Rizk R Y, Abd El-Fattah F K, Squartini A, Corich V, Giacomini A, de Bruin F, Rademaker J, Mayra-Flores J, Ostrom P, Vega-Hernandez M, Hollingsworth R I, Martinez-Molina E, Mateos P, Velazquez E, Wopereis J, Triplett E, Umali-Garcia M, Anarna J A, Rolfe B G, Ladha J K, Hill J, Mujoo R, Ng P K and Dazzo F B 2001 The beneficial plant growth-promoting association of Rhizobium leguminosarum bv. trifolii with rice roots. Aust. J. Plant Physiol. 28, 845–870.Google Scholar