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Plant pathogen forms an intimate relationship with the plants to gain access to the host resources required for its growth, reproduction and survival. The process of infection, colonization and pathogen reproduction is referred to as pathogenesis. Disease outcome is determined by three-way interaction of the pathogen, plant and the environment, an interaction known as disease triangle (Figure 1). However, to avoid disease infestation, the plant must either recognize the presence of potential pathogens or mount a defence response to prevent pathogen attack without it being detrimental to its own physiology. The genetic constitution and the environmental conditions under which the genes operate govern the ability of a plant to defend itself against pathogen. Preformed plant structures and compounds that resist pathogen entry are cell walls, cuticle/surface, antimicrobial proteins & chemicals, enzyme inhibitors and detoxifying enzymes that breakdown pathogen derived toxins. Such attributes of host plant lower the chances of disease infection. The pathogen invades the host and encounters the pre-existing physical