ABSTRACT
Biological control is the use of natural or modified organisms, genes, or gene products, to reduce the effects of undesirable organisms such as plant pathogens and to favor desirable organisms such as crops (Research Briefings, 1987). This definition is broad and includes genetic modification (genetic resistance) of the host plant. However, the main focus of this chapter will be on natural and modified organisms as biological control agents of plant pathogens. Biocontrol agents are known also as antagonists and antagonism is the generalized mechanism that they use to reduce the survival or diseasecausing activities of plant pathogens. Antagonism is actively expressed opposition and includes antibiosis, competition and parasitism. Biological control of plant diseases with antagonists is accomplished by destroying existing pathogen inoculum, excluding the pathogen from the host plant, or suppressing or displacing the pathogen after infection has occurred (Cook and Baker, 1983).
