ABSTRACT
78The crop production and protection techniques which we all follow today have caused considerable damage to our soil and water. So, microbiologists and plant pathologists are facing an urgent challenge of the development of environment friendly alternatives for chemical pesticides for combating crop diseases. Biological control of plant diseases involving use of antagonistic microorganisms offers an excellent alternative to pest management by chemicals. It can be achieved by either promoting the native antagonists to reach a density sufficient to suppress a pathogen(s) or introducing alien antagonists. An important group of the microbial communities, existing in rhizosphere, which exert beneficial effects on plant growth upon root colonization, are termed as plant growth-promoting rhizobacteria (PGPR). These PGPR have been considered important in sustainable agriculture because of their biocontrol potentials and plant growth promotional activities. Many strains of Pseudomonas fluorescens and related fluorescent Pseudomonas spp. show potential for biological control of phytopathogens especially root pathogens. The fluorescent pseudomonads include all Pseudomonas sp. with the ability to produce fluorescent pyoverdine siderophore (also known as pseudobactin). The modes of action that play a role in disease suppression by these bacteria include: siderophore mediated competition for iron, antibiosis, production of lytic enzymes, and induced systemic resistance (ISR). Superior root colonization and effective functioning in the rhizosphere are the key criteria when selecting strains and researches aim at better understanding the molecular basis of these traits and the signaling process regulating the ecology of these bioagents in situ. Current genomic analysis for rhizosphere competence and biocontrol traits will likely lead to the development of novel tools for effective management of indigenous and inoculated fluorescent pseudomonads biocontrol agents and a better exploitation of their plant-beneficial trait for sustainable agriculture.
