Synergistic Biocontrol and Plant Growth Promotion by Indigenous Rhizospheric Microbial Consortia Against Soil-Borne Phytopathogens

Sustainable management of crop diseases is critical to reduce reliance on chemical pesticides and preserve soil health. This study isolated 72 indigenous rhizospheric microorganisms (50 bacteria, 22 fungi) from tomato, chilli, and brinjal soils in Barshi, Maharashtra, India, and evaluated their dual potential for plant growth promotion (PGP) and biocontrol. Molecular identification revealed dominant antagonists as Bacillus subtilis (BS10), Pseudomonas fluorescens (PF4), and Trichoderma harzianum (T2). These isolates exhibited multiple PGP traits, including indole-3-acetic acid production (24–31 µg mL⁻¹), phosphate solubilization (index 2.8–3.4), siderophore production (60–75%), and ACC deaminase activity (0.54–0.62 µmol α-KB mg⁻¹ h⁻¹). Strong hydrolytic enzyme activity and antifungal inhibition (up to 85.7%) were observed in vitro against Fusarium oxysporum, Rhizoctonia solani, and Pythium ultimum. Greenhouse trials on tomato plants showed significant disease suppression (77.9% reduction in Disease Severity Index) and improved shoot, root, and biomass parameters. Principal Component Analysis indicated that enzyme-linked biocontrol and PGP traits accounted for 87.4% of total variance, demonstrating synergistic interactions. These findings highlight the potential of locally adapted Bacillus, Pseudomonas, and Trichoderma isolates as eco-friendly bioinoculants, offering a sustainable strategy for soil-borne disease management and crop productivity enhancement.