Isolation and characterization of a fungal isolate for phosphate solubilization and plant growth promoting activity

Varsha Nenwani, Pratima Doshi, Tithi Saha and Shalini Rajkumar*

Department of Biochemistry and Biotechnology, Institute of Science, Nirma University, Sarkhej – Gandhinagar Highway, Ahmedabad Gujarat 382 481, India.

*Corresponding author. E-mail: shalini_rjk@yahoo.com. Tel: 91-2717-241900-04. Ext. 627. Fax: 91-2717-241916.

Accepted 21 December, 2009

   Abstract

A fungal species namely F1 was isolated from the rhizosphere on the basis of its ability to form halos (zone of solubilization) on Pikovskaya’s agar. F1 was assessed for phosphate solubilization, titratable acidity (TA), gluconate concentration and change in pH over incubation period of 21 days and other plant growth promoting traits. F1 solubilized maximum inorganic phosphorus (662 μg P ml^-1) from tricalcium phosphate present in the Pikovskaya’s broth on 18th day. The TA followed a similar trend as that of P solubilized, except on day 21 when the value that for TA was highest. A similar pattern was also observed with production of gluconic acid, for which a constant value of 8.96 × 10^-4 g% was observed till 18th day of incubation. However, gluconic acid was not the only organic acid produced in the culture broth, because the amount of gluconic acid produced did not relate to the high values observed for P solubilized and TA. Efficiency of the F1 to solubilize phosphate from organic reserves was determined by performing assays of phosphatases and phytases. The culture F1 produced 1.86 and 1.90 EU of enzymes alkaline and acid phosphatase, respectively and phytase activity was 28 mU. The concentration of catechol and hydroxymate type siderophores produced by F1 was 4.50 and 4.55 µgml^-1 respectively and it also produced 11.45 µgml^-1 of IAA which is significantly high. Some fungi may possess traits associated with biocontrol of plant pathogens such as production of enzyme chitinase which was 0.037 EU for F1. On the basis of cultural and microscopic features, the isolate F1 could be Absidia spp. and has potential of being a competent bioinoculant.

Key words: Phosphate solubilization, bioinoculant, plant growth promoting fungus (PGPF).