Journal of Pure and Applied MicrobiologyVol. 6 No. 4

Biological Activities of Plant Growth Promoting Azotobacter sp. Isolated from Vegetable Crops Rhizosphere Soils

K. Ponmurugan1,2*, A. Sankaranarayanan1 and Naif Abdullah Al-Dhabi2

1Department of Microbiology, K.S.Rangasamy College of Arts and Science, Tiruchengode - 637 215, India. 2Department of Botany and Microbiology, Addiriyah Chair for Environmental Studies, College of Science, King Saud University, Riyadh – 11451, Saudi Arabia.

Received on 04 May 2012 and accepted on 10 June 2012



A total of one hundred and fifty rhizospheric soil samples were collected from the different vegetable (tomato, egg plant, chilli) growing fields in and around Namakkal district, Tamil Nadu, India. Ten isolates of Azotobacter sp. were isolated from the rhizospheric soils of vegetable plants using Jenson’s and Ashby’s mannitol selective media. The isolated Azotobacter strains were characterized and identified based on morphological and biochemical characteristics. Multiple plant growth promoting activities of Azotobacter isolates were determined in terms of IAA production, NH3 release, PO4 solubilization, HCN and siderophore production. IAA production of the Azotobacter isolates were tryptophan concentration dependent. Most of the Azotobacter isolates were tolerant to zinc and mercury concentration of 100-200 µg/ml. Antifungal activity of the Azotobacter was determined against Aspergillus flavus, Cercospora sp. and Fusarium oxysporum and found higher zone of inhibition (18-26 mm) at higher concentration of culture suspension.

Keywords : Rhizospheric soil, Plant growth promoting activities, Heavy metal tolerance, Antiphytopathogenic fungal activity.