ABSTRACT
The microbial antagonism that is seen in biological control of plant pathogens is broadly based on the categories of competition (for nutrients and space), parasitism (which may be by the production of volatile or nonvolatile antibiotics), and hyperparasitism. A dual culture system on agar plates of the target and the potential antagonist can detect several different classes of antagonism, including antibiosis, competition, and hyperparasitism. A great number of saprophytic microorganisms compete for nutrients and space in the rhizosphere, and can give a significant degree of biological control of soil-borne plant pathogens. Microbial antagonism has often been considered as occurring mainly externally to the plant, in the phylloplane, rhizosphere, or in the bulk soil. Competition for nutrients and space, the production of antibiotics, and hyperparasitism all play important roles in the antagonism of pathogens arriving and persisting in the phyllosphere. Epiphytic microorganisms take up nutrients rapidly, resulting in rapid reductions in the amounts of nutrients available to pathogens.
