Screening and assessment of PGP and biocontrol properties of Azotobacter species isolated from agriculture soils of North Karnataka

Plant growth-promoting rhizobacteria (PGPR) are recognized for their ability to produce phytohormones, root-stimulating compounds, anti-fungal compounds and other secondary metabolites, making them potential biocontrol agents in agriculture. In the present study, 85 Azotobacter isolates were isolated from the agricultural soils of Raichur and Chikkabalapura locations. The isolates were further accessed for morphological, biochemical and plant growth-promotion (PGP) properties. All the isolated strains showed brown to black colour colonies on the Waksmann 77 media plate. Similar biochemical results were obtained for all the Azotobacter isolates. The isolates such as Azt-85 recorded the highest N2 fixation (33.36 µgN/mL/Day), Azt-69 produced IAA (24.67 µg/mL), and Azt-51 produced GA (23.7 µg/25mL). The anti-fungal efficacy studies were conducted using the dual culture technique using the efficient PGPR Azotobacter isolates against fungal species (Fusarium oxysporum f. sp. lini, Fusarium oxysporum f. sp. ciceris and Aspergillus flavus). After the incubation period, the Azt-41 isolate showed the highest zone of inhibition (18 mm) against Fusarium oxysporum f. sp. lini. Similarly, Azotobacter isolates viz., Azt-25, 38 and 41 showed maximum growth inhibition (9 mm) against Fusarium oxysporum f. sp. ciceris. Similarly, the Azt-31 isolate recorded a moderate (13 mm) zone of inhibition against Aspergillus flavus. Integrating sustainable biocontrol strategies by injecting beneficial microbes like Azotobacter can enhance resilient food production systems and reduce reliance on chemical inputs through PGPR properties.