ABSTRACT
In the evolutionary process, both bio-control agents and pathogen evolved with time but it is evident that biological control has primacy over phytopathogens. Bio-control agents have evolved some mechanism to suppress the pathogen such as competition for space and nutrients, production of antimicrobial substances or antibiosis, parasitism and predation, induction of defense response in plants and metabolism of germination stimulants. This chapter describes about the evolution of biological control agents with detailed mode of action and their mechanism against plant pathogens especially soil borne. The results of many years of research with Trichoderma species as biocontrol agents has shown that not all the mechanisms and characteristics deemed necessary for optimum biocontrol are found in the same organism. The production of hybrids from Trichoderma species, many of which have no known sexual stage, will entail the use of transformation or protoplast fusion in order to obtain strains with optimal sets of characteristics.
