Microbial interactions and biocontrol in the rhizosphere

The loss of organic material from the roots provides the energy for the dev elopment of active microbial populations in the rhizosphere around the root . Generally, saproptrophs or biotrophs such as mycorrhizal fungi grow in th e rhizosphere in response to this carbon loss, but plant pathogens may also develop and infect a susceptible host, resulting in disease. This review e xamines the microbial interactions that can take place in the rhizosphere a nd that are involved in biological disease control. The interactions of bac teria used as biocontrol agents of bacterial and fungal plant pathogens, an d fungi used as biocontrol agents of protozoan, bacterial and fungal plant pathogens are considered. Whenever possible, modes of action involved in ea ch type of interaction are assessed with particular emphasis on antibiosis, competition, parasitism, and induced resistance. The significance of plant growth promotion and rhizosphere competence in biocontrol is also consider ed. Multiple microbial interactions involving bacteria and fungi in the rhi zosphere are shown to provide enhanced biocontrol in many cases in comparis on with biocontrol agents used singly. The extreme complexity of interactio ns that can occur in the rhizosphere is highlighted and some potential area s for future research in this area are discussed briefly.