Phosphate-Solubilizing Indigenous Rhizobacteria as Biological Suppressors of Fusarium oxysporum

Soil-borne fungal diseases significantly reduce agricultural productivity, with Fusarium oxysporum being a major vascular wilt pathogen due to its root infection ability, soil persistence, and adaptability. The widespread use of fungicides raises environmental and resistance concerns, highlighting the need for sustainable alternatives. This study focused on isolating indigenous rhizobacteria capable of suppressing F. oxysporum and solubilizing phosphate to serve as eco-friendly microbial inoculants. Rhizosphere soils from organically managed soybean and chickpea fields in Maharashtra, India, were sampled, resulting in 27 bacterial isolates (RB1–RB27). Phosphate solubilization was tested on Pikovskaya’s and NBRIP agar by measuring the solubilization index (SI) and quantified in NBRIP broth over eight days. Antagonistic activity against F. oxysporum was assessed using dual culture assays on PDA. Phosphate solubilization varied, with RB11 showing the highest SI (8.32), followed by RB7 (7.28) and RB9 (7.05). In liquid culture, RB3 released the most soluble phosphate (295 µg mL⁻¹). All isolates inhibited Fusarium growth compared to the control (59.35 mm), with RB7 and RB11 showing strong inhibition zones (8–8.5 mm) and per cent inhibition ranging from 76.21% to 91.31%, highest in RB3