Molecular and biochemical aspects of rhizobacterial ecology with emphasis on biological control

The rhizosphere is the narrow zone of soil surrounding the root that is sub ject to influence by the root. Rhizobacteria are plant-associated bacteria that are able to colonize and persist on roots. An understanding of the eco logy of a microorganism is a fundamental requirement for the introduction o f a microbial inoculant into the open environment. This is particularly tru e for biological control of root pathogens in the rhizosphere, where one is actively seeking to alter the ecological balance so as to favour growth of the host plant and to curtail the development of pathogens. Some strains o f plant growth-promoting rhizobacteria can effectively colonize plant roots and protect plants from diseases caused by a variety of root pathogens and growth promotion of plants through direct stimulation of growth hormone. S uch beneficial or plant health-promoting strains are emerging as promising biocontrol agents. They are suitable as soil inoculants either individually or in combination and may be compatible with current chemical pesticides. Considerable progress has been achieved using molecular genetic techniques to elucidate the important microbial factors or genetic traits involved in the suppression of fungal root diseases. Strategies utilizing molecular gen etic techniques have been developed to complement the ongoing research rang ing from the characterization and genetic improvement of a selected biocont rol agent to the measurement of its persistence and dispersal. Finally, bio control is considered as part of a disease control strategy like integrated pest management which offers a successful approach for the deployment of b oth agro-chemicals and biocontrol agents.