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.