Characterization of plant growth promoting rhizobacteria associated with chickpea (Cicer arietinum L.)

Plant growth promoting rhizobacteria (PGPR) are known to influence plant growth by various direct or indirect mechanisms. In search of efficient PGPR strains with multiple activities, a total of 150 bacterial isolates belonging to Bacillus, Pseudomonas, Azotobacter and Rhizobium were isolated from different rhizospheric soil of chick pea in the vicinity of Allahabad. These test isolates were biochemically characterized and screened in vitro for their plant growth promoting traits like production of indoleacetic acid (IAA), ammonia (NH3), hydrogen cyanide (HCN), siderophore and catalase. All the isolates of Bacillus, Pseudomonas and Azotobacter produced IAA, whereas only 85.7% of Rhizobium was able to produce IAA. Production of ammonia was commonly detected in the isolates of Bacillus (95.0%) followed by Pseudomonas (94.2%), Rhizobium (74.2%) and Azotobacter (45.0%). All test isolates were positive for catalase but none of the isolates produced HCN. On the basis of multiple plant growth promoting activities, 20 bacterial isolates of each genus, in total 80 isolates, were evaluated for their heavy metal tolerance. Among these isolates, Bacillus spp. were tolerant to all the heavy metals (400 µg ml-1), whereas Pseudomonas spp. were tolerant to Hg (100 µg ml-1), Co (100 µg ml-1), Cd (200 µg ml-1), Cr (100 µg ml-1), Cu (200 µg ml-1), Pb (400 µg ml-1), Zn (200 µg ml-1). Tolerance to heavy metals was observed less frequently in Azotobacter spp. and Rhizobium spp. The isolates could exhibit more than two or three PGP traits, which may promote plant growth directly or indirectly or synergistically. Further, rhizobacteria tolerant to multiple heavy metals exhibited a couple of PGP activities.