Technical Abstract: Bacterial secondary metabolites active in suppression of root diseases include antibiotics, siderophores and volatile compounds. With recombinant DNA technology it is possible to elucidate the regulatory mechanisms and structural genes involved in the production of these metabolites and to transfer genes for specific beneficial traits among bacterial strains. Some "transgenic" rhizobacteria that express such genes have provided greater protection against fungal pathogens of plants in growth chamber studies, indicating that genetic manipulation is a viable approach to the development of microbial biocontrol agents that are safe, reliable and effective