Biological Control of Plant Pathogens by Antibiotic-Producing Bacteria

Natural biological control phenomena are very complex systems consisting of integrated biotic and abiotic factors which are influenced by seasonal changes. Mechanisms such as competition, hyperparasitism, cross protection and antibiosis, may explain the pathways of the phenomenon of biological control. Antibiosis occurs when compounds produced by certain microorganisms have harmful effects on others. Selection for antibiotic producing bacteria begins with in vitro tests but ought to be followed by in vivo experiments. Purification, identification and application of the antibiotic as compared to the application of the antagonist itself, reveals the importance of antibiosis as part of the whole antagonistic phenomenon. Isolates of biocontrol agents which lack the gene for the antibiotic and are less effective against their target pathogens, strengthen the significance of antibiosis. Unfortunately, the correlation between results of in vitro tests and of field experiments is very small. Bacteria are less resistant than other biocontrol agents (yeasts, filamentous fungi) to adverse environmental conditions such as humidity and UV radiation.