Growth enhancement of Sesamum indicum L. by rhizosphere-competent Azotobacter chroococcum AZO2 and its antagonistic activity against Macrophomina phaseolina

Indigenous strains isolated from rhizosphere may contain highly competent genotypes to enhance the plant growth and often perform better than the introduced isolates. The present study deals with the characterisation of plant growth-promoting (PGP) attributes and antagonistic activity of Azotobacter chroococcum AZO2 against Macrophomina phaseolina causing charcoal rot disease and their effect on the growth of sesame (Sesamum indicum L.). Eight strains of Azotobacter were isolated from sesame rhizosphere on nitrogen-free medium, which exhibited significant PGP parameters such as phosphate solubilisation, indole acetic acid and siderophore production. The strain A. chroococcum AZO2 (EU274299) was characterised by 16S rDNA gene sequencing. Amplification of 781 bp nif H gene confirms nitrogenase activity of all the strains. A. chroococcum AZO2 exhibited strong antagonistic activities against M. phaseolina causing 81% colony growth inhibition and resulted in hyphal perforations, empty cell (halo) formation, hyphal twisting, shrinking and lysis of fungal mycelia along with degeneration of sclerotia. A. chroococcum AZO2 produced chitinase that caused degradation and digestion of the cell wall component of M. phaseolina. Different vegetative and reproductive parameters of sesame were found to be enhanced significantly upon application of A. chroococcum AZO2 + half doses of chemical fertilisers. A. chroococcum AZO2 was also found to be an effective root coloniser, plant growth promoter and potential antagonistic bacterium. It can be concluded that A. chroococcum AZO2 strain bears the characteristics of technological applications for inoculant preparation and growth enhancement of sesame besides being utilised as a better PGP bacterium as well as an effective agent for biocontrol of M. phaseolina.