ABSTRACT
In an ecosystem, diverse but balanced biological factors arising from long-term coevolution, interact with host plants and soilborne microbial plant pathogens in different environmental conditions. Under wild ecosystem, the plants and the pathogens coexisted in a balanced level. When selection of plant species was made for domestication, resistance to diseases was not given equal importance, as in the case of yield and quality of produce. This attitude resulted in disturbance in natural balance of coexistence of host plant species and microbial pathogens. Ultimately increase in susceptibility of crop plants forced the researchers to search for resistance gene(s) in wild relatives of crop plant species. Thus, the crops became susceptible, not only to the soilborne microbial plant pathogens present in a geographic location, but also to the exotic plant pathogens introduced through seeds and propagules (Narayanasamy 2017). This situation warranted enforcement of regulatory methods to prevent introduction of plant pathogens from other countries or from one region to another region within a country. Such introduction of exotic microbial plant pathogens may lead to epidemics that can be ecologically and economically difficult to contain.
