Abstract: The main objective of present study was to evaluate the phyllospheric bacteria for their auxin production and plant growth promoting potential under axenic conditions. Bacterial strains were isolated from the phyllosphere of different plants and screened for in vitro auxin production in the presence of precursor L-tryptophan. Finally, 7 isolates (BjP-2, BjP-5, CsP-1, CsP-6, ZmP-3, ZmP-4, SpP-6) that released maximum auxin levels were selected to evaluate the phytostimulatory effect on Cicer arietinum L. under axenic conditions. Antibiotic susceptibility pattern of strains was evaluated by using different antibiotic discs. Maximum auxin production was recorded with strain CsP-1 (85 µg ml-I) when medium was supplemented with 250 µg ml-I L-tryptophan. Antibiotic susceptibility pattern of phyllobacterial strains was also evaluated by using six different types of antibiotic discs. Results showed that strains BjP-2, CsP-1, CsP- 6, ArP-1, ZmP-3, ZmP-4, BjP-4 and SpP-5 were resistant to erythromycin (15 µg) ampicillin (10 µg) and oxytetracyclin (30 µg). In pot trials, majority of the treatments showed significant improvements in different growth parameters amended with 250 µg g-I of soil. It was obesrved that strain CsP-1, ZmP-4 and SpP-6 showed the most promising results for shoot length, root length and plant biomass. Strain CsP-1 showed up to 190%, 160%, 50% and 32% increases for shoot length, root length, fresh and dry biomass, respectively, over control. It can be concluded that phyllosphere of plants can be screened to select agriculturally important bacteria on the basis of their auxin production.
Keywords: Phyllobacteria, phytostimulatory effects, plant growth promotion, Cicer arietinum, plant growth promoting rhizobacteria.