A review on rhizospheric bacteria for biological control of important soil borne pathogens

Rhizospheric bacteria have emerged as effective Biological Control Agents (BCAs) against soil- borne pathogens, promoting sustainable agricultural practices. The rhizosphere, influenced directly by root exudates, is a critical zone of intense microbial interactions, housing diverse beneficial bacteria including genera such as Pseudomonas, Bacillus, Azotobacter, Rhizobium, Enterobacter, and Burkholderia. These microbes enhance plant health through multiple biocontrol mechanisms. Direct biocontrol mechanisms include competitive exclusion, antibiotic and bacteriocin production, siderophore-mediated iron sequestration, quorum sensing interference, and enzymatic pathogen degradation. Notably, Pseudomonas fluorescens produces antibiotics like phenazine-1-carboxylic acid, pyoluteorin, pyrrolnitrin, and 2,4- diacetylphloroglucinol, effectively suppressing pathogens such as Fusarium spp., Rhizoctonia solani, and Pythium ultimum. Bacillus species produce broad-spectrum antifungal antibiotics including iturin, fengycin, and zwittermicin A, significantly contributing to disease management. Bacteriocins further aid suppression by targeting closely related pathogenic strains. Indirect mechanisms involve inducing plant Induced Systemic Resistance (ISR), preparing plants against pathogen invasions through signaling pathways mediated by jasmonic acid and ethylene. Additionally, rhizospheric bacteria enhance plant growth via phosphorus solubilization, nitrogen fixation, and phytohormone synthesis, boosting plant vigor and disease tolerance. However, the practical application of these BCAs faces challenges such as inconsistent field performance due to environmental variability, limited understanding of complex microbial interactions, and difficulties in formulating stable and effective microbial consortia. Advances in molecular approaches such as metagenomics, transcriptomics, and metabolomics have deepened understanding of plant-microbe interactions, identifying key biocontrol genes and metabolites. This facilitates the development of targeted bioformulations, particularly multi-strain bacterial consortia (MSBCAs), which offer enhanced colonization efficiency and consistent pathogen suppression. Amid rising environmental concerns about chemical pesticides, rhizospheric bacteria provide sustainable alternatives, contributing significantly to the advancement of eco- friendly agricultural practices.