BIOCONTROL WITHIN THE CONTEXT OF SOIL MICROBIAL COMMUNITIES: A Substrate-Dependent Phenomenon.

Broad spectrum biological control of diseases caused by soilborne plant pathogens such as Pythium, Phytophthora, and Rhizoctonia solani requires the introduction into or presence of edaphic sources of organic nutrients in soil for sustenance of biocontrol agents. The decomposition level of organic matter critically affects the composition of bacterial taxa as well as the populations and activities of biocontrol agents. Competition, antibiosis, parasitism, and systemic induced resistance are all affected. Highly stabilized sources of Sphagnum peat consistently fail to support sustained biological control, even when inoculated with biocontrol agents. Composts, on the other hand, can serve as an ideal food base for biocontrol agents and offer an opportunity to introduce and establish specific biocontrol agents into soils, which in turn leads to sustained biological control based on the activities of microbial communities.