Phosphate solubilization activity of rhizobia native to Iranian soils
- 301 Downloads
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.
Keywordscalcium phosphate legumes inositol hexaphosphate PGPR pH Rhizobium
The authors are grateful to professor Malakouti head of the Soil and Water Research Institute in Tehran and to the staff of the Department of Soil Biology of the same Institute for their help with the rhizobial collection and for their constructive discussions. Many thanks to professor Ghannadha for his help in the statistical analyses and the interpretation of the results, and to Miss Pashaky for her excellent technical assistance. Financial support for this investigation was provided by grants from the Iranian Government “Studies and Researches Between Universities” program for collaboration between the Universities of Tehran and Rafsanjan.
- Goldstein A H (1986) Bacterial solubilization of mineral phosphates: historical perspectives and future prospects. Am. J. Altern. Agric. 1:51–57Google Scholar
- Gupta R, Singal R, Shankar A, Kuhad R C, Saxena R K (1994) A modified plate assay for screening phosphate solubilizing microorganisms. J. Gen. Appl. Microbiol. 40:255–260Google Scholar
- Halder A K, Chakrabartty P K (1993) Solubilization of inorganic phosphate by Rhizobium. Folia Microbiol. 38:325–330Google 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, USAGoogle Scholar
- Richardson A E (2001) Prospects for using soil microorganisms to improve the acquisition of phosphorus by plants. Aust. J. Plant Physiol. 28:897–906Google Scholar
- SAS, Institute Inc 1990 SAS procedure guide version 6 edn. SAS Institute Inc Cary, NC, 705 pGoogle Scholar
- Silva Filho G N, Vidor C (2000) Phosphate solubilization by microorganisms in the presence of different carbon sources. R. Bras. Ci. Solo. 24:311–319Google Scholar
- Somasegaran P and Hoben H J 1994 Handbook for Rhizobia – Methods in Legume–Rhizobium Technology. Springer-Verlag, New YorkGoogle Scholar
- Vincent J M 1970 A Manual for the Practical Study of Root Nodule Bacteria. IBP handbook 15 Blackwell Scientific Publications, OxfordGoogle 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, Dazzo F B (2001) The beneficial plant growth-promoting association of Rhizobium leguminosarum bv. trifolii with rice roots. Aust. J. Plant Physiol. 28:845–870Google Scholar