ECOLOGICAL BASIS OF BIOLOGICAL-CONTROL OF SOILBORNE PLANT-PATHOGENS

Most soilborne plant pathogens adapt well within their ecosystems. They are active under favorable conditions but inactive or dormant under adverse conditions and, in most cases, are able to escape competitive or parasitic pressure from other microorganisms. Numerous reports indicate that biological control of soilborne pathogens by the introduction of hyperparasitic or antagonistic microorganisms into the soil can be successful. In this review the ecological significance of antagonism and hyperparasitic organisms in the control of soilborne plant pathogens is discussed, using several economically important diseases as examples. The review emphasizes the need for basic understanding of the versatility of pathogens and the diversity and complexity of interactions among pathogen, biological control agent, and plant in a given soil environment. The prospect of improving the effectiveness of an introduced biological control agent by modification of the soil environment is also discussed.