The key to achieving successful, reproducible biological control is the gradual appreciation that knowledge of the ecological interactions taking place in soil and root environments is required to predict the conditions under which biocontrol can be achieved ( Deacon, 1994 Whipps, 1997 a ) and, indeed, may be part of the reason why more biocontrol agents are reaching the market‐place ( Fravel, 1999 Whipps and Lumsden, 2001 Whipps and Davies, 2000 ). Interest in biological control has increased recently fuelled by public concerns over the use of chemicals in the environment in general, and the need to find alternatives to the use of chemicals for disease control. The microbial interactions taking place in the spermosphere and rhizosphere associated with disease development and especially biocontrol of these diseases form the background of this review.

However, antagonistic symbioses between pathogens and roots can also form resulting in disease. For example, mutualistic biotrophic symbioses may develop between Rhizobia and legumes, and mycorrhizal fungi may interact with their plant hosts. Although the stimulation in microbial activity is a general phenomenon largely involving saprotrophs, specific groups of symbionts may be selectively enhanced. IntroductionĪs seeds germinate and roots grow through the soil the loss of organic material provides the driving force for the development of active microbial populations around the root, known as the rhizosphere effect ( Whipps, 1990 Morgan and Whipps, 2001 ). The extreme complexity of interactions that can occur in the rhizosphere is highlighted and some potential areas for future research in this area are discussed briefly.īacteria, biocontrol, fungi, roots, soil.

Multiple microbial interactions involving bacteria and fungi in the rhizosphere are shown to provide enhanced biocontrol in many cases in comparison with biocontrol agents used singly. The significance of plant growth promotion and rhizosphere competence in biocontrol is also considered. Whenever possible, modes of action involved in each type of interaction are assessed with particular emphasis on antibiosis, competition, parasitism, and induced resistance.

The interactions of bacteria used as biocontrol agents of bacterial and fungal plant pathogens, and fungi used as biocontrol agents of protozoan, bacterial and fungal plant pathogens are considered. This review examines the microbial interactions that can take place in the rhizosphere and that are involved in biological disease control. Generally, saproptrophs or biotrophs such as mycorrhizal fungi grow in the rhizosphere in response to this carbon loss, but plant pathogens may also develop and infect a susceptible host, resulting in disease.

The loss of organic material from the roots provides the energy for the development of active microbial populations in the rhizosphere around the root.

How to apply biocontrol agents to soil