ABSTRACT
Plant diseases result from the interaction of a pathogen with its host but the intensity of this interaction is markedly affected by the environmental factors. The pathogen interacts with the host and vice versa. Development of disease in the plant is not a sudden effect. A chain of events are responsible for causation of any disease. These stages, reactions, and interreactions arranged in a sequence lead to disease development and the entire chain of events leading to disease development is known as "pathogenesis" The means of survival are the first link in infection chain or disease cycle. Plant infection is influenced by many factors not only in the initial invasion but also in the subsequent spread of disease; hence these factors are of critical importance in epidemiology. Zoospore penetration typically involves encystment of zoospore on the outer surface of host cell and subsequent development of an expanding vacuole within the cyst.
