ABSTRACT
Pathogenesis is the chain of events that lead to development of disease in the host (or) sequence of progress in disease development from the initial contact between the pathogen and its host to the completion of the syndrome. Frequently, a disease cycle is practically identical to a pathogen's life cycle, with the important difference being that a disease cycle largely depicts the disease as it develops due to the interaction between the host plant and the pathogen. Plant viruses are particulate in nature and they do not have any capacity to enter the host cell so they do not make any aggressive effort for entry, but depend on different insect vectors for their entry into host cell. Fungal invasion is chiefly by germ tubes or structures derived from them. Fungi spread into all parts of host organs, either by growing directly through the cells as an intracellular mycelium or by growing between the cells as an intercellular mycelium.
