In phytopathology, antagonism refers to the action of any organism that suppress or interfere the normal growth and activity of a plant pathogen, such as the main parts of bacteria or fungi.
These organisms can be used for pest control and are referred to as ``Biological Control Agents´´. They may be predators, parasites, parasitoides, or pathogens that attack harmful insect, weed or plant disease or any other organism in its vicinity . the inhibitory substance is highly specific in its action affecting only a specific species. many soil microorganisms are antagonistic .they secrete a potent enzyme which destroys other cells by digesting their cell walls and degrade the cellular material as well as d released protoplasmic material serves as a nutrient for the inhibitor organism for example Aspergillus has an antagonistic effect on Penicillium and Cladosporium . Trichoderma has an effect on actinomycetes. Pseudomanas show antagonism on Cladosporium.