Ecological Occurrences of Multitrait Azotobacter in different Crop Rhizospheres of Assam

Abstract

A study was undertaken to exploit prospective Azotobacter from different crop rhizospheres of Assam. Based on the nitrogenase activity, twelve Azotobacter isolates representing rhizosphere samples from rice, toria and wheat were isolated in Burk’s media using serial dilution technique. Higher populations of Azotobacter was observed in wheat (7.22 × 104 cfu g-1 soil) and toria (6.02 × 104 cfu g-1 soil) rhizosphere compared to rice rhizosphere (2.35 × 104 cfu g-1 soil). Organic carbon (OC) of the rhizospheres appeared to be the strongest factor (r = 0.91*) causing variation in Azotobacter population across rhizospheres. All the twelve isolates produced pigments, exopolysaccharides, indole acetic acid (IAA) and gibberellic acid (GA) at varying degrees. However, only seven isolates could produce siderophore and five of them could produce hydrocyanic acid (HCN). Five isolates (Azo03, Azo05, Azo08, Azo25 and Azo52) showing production of IAA, GA, siderophore and HCN were further evaluated for their biochemical traits and intrinsic antibiotic resistance (IAR) potentials. The isolates differed specifically in assimilating different carbohydrates and IAR profiles. The isolates showed decarboxylase activity and could ferment citrate as sole carbon source, and therefore were highly prolific in the rhizosphere.