Screening and Characterization of Native Microbial Antagonists for the Development of a Multi-Strain Biocontrol Consortium against Ralstonia solanacearum

Abstract

Bacterial wilt caused by Ralstonia solanacearum remains difficult to manage sustainably, creating a need for compatible native microbial antagonists with complementary biocontrol traits. This study isolated four rhizosphere microorganisms—Trichoderma viride (Tv), Pseudomonas fluorescens (Pf), Bacillus subtilis (Bs) and Azotobacter chroococcum (Ac)—from healthy eggplant plants surviving in bacterial-wilt-affected fields and assessed their antagonistic, biochemical, plant-growth-associated and compatibility characteristics. In dual-culture assays, Pf showed the highest inhibition of R. solanacearum (68.50%; 18.40 mm inhibition zone), followed by Bs (55.40%; 15.60 mm). Hydrolytic enzyme screening indicated overlapping amylase, protease and lipase activities among the antagonists, with Bs showing a 16.5 mm protease clearance zone and Pf a 14.2 mm zone. Siderophore screening showed the largest CAS halo for Pf (22.40 mm), which also exhibited a strong positive reaction for HCN production. Ac produced the highest indole-3-acetic acid concentration (32.60 µg/ml), followed by Pf (28.40 µg/ml). Cross-streak assays showed no visible inter-strain inhibition among Tv, Pf, Bs and Ac under the tested conditions. These findings indicate complementary in vitro functional traits and preliminary mutual compatibility among the four isolates, supporting their further evaluation as candidate components of a multi-strain biocontrol consortium. Molecular identification, formulation assessment and greenhouse and field validation remain necessary before practical application.