Characterization of Plant Growth Promoting Rhizobacteria Isolated from Chickpea (Cicer arietinum)

Aims: To isolate bacterial strains from chickpea rhizospheric soil and nodules, to characterize and identify potential bacterial strains by using 16S rRNA gene sequencing.
Place and Duration of Study: Department of Soil Science & SWC, PMAS, Arid Agriculture University, Rawalpindi Pakistan between July 2010 and July 2011.
Background: Plant growth promoting rhizobacteria are being preferred nowadays as inoculants for influencing crops via multiple direct or indirect mechanisms but screening to find out the effective PGPR strains is one of the crucial steps. This research is aimed at keeping in view their potential for phosphate solubilization, indole acetic acid and ammonia production.
Methodology: Extensive survey was carried out in Pothwar (District, Rawalpindi, Attock and Chakwal) for collection of chickpea rhizospheric soil and root nodules. The isolation of rhizospheric soil bacteria was performed by using dilution plate technique while the root nodules bacteria were isolated on yeast extract mannitol agar supplemented with congo red. Ten bacterial strains designated as AM-1 to AM10 were isolated, purified and characterized for phosphate solubilization, indole acetic acid (IAA) and ammonia production. These bacterial strains were identified as belonging to species of Bacillus, Enterobacter, Pseudomonas, Rhizobium, Sphingobacterium, Pantoea and Chryseobacterium. All bacterial strains solubilized phosphate and produced IAA. Two bacterial strains AM-5 (Sphingobacterium canadense) and AM-4 (Rhizobium pusense) solubilized the maximum amount of phosphate i.e. 273.84 µg ml-1 and 262.83 µg ml-1 respectively with a significant pH drop from 7 to 2.67. These strains proved positive for ammonia production. Six most potential and identified strains were selected on the basis of plant growth promoting activities.
Conclusion: AM-4 (Rhizobium pusense) and AM-5 (Sphingobacterium canadense) are efficient strains and there is a need of inoculation experiments under control and field conditions to use these stains as biofertilizer to enhance the growth and productivity of the chickpea.