ABSTRACT
In general plants defend themselves against pathogens by two ways: structural or morphological characteristics that act as physical barriers and biochemical reactions that take place in cells and tissues that are either toxic to the pathogen or create conditions that inhibit the growth of the pathogen in the plant. Antimicrobial substances pre-existing in plant cells include unsaturated lactones, cyanogenic glycosides, sulphur containing compounds, phenols, phenolic glycosides and saponins. Several phenolic compounds, tannins, and some fatty acid like compounds such as dienes, which are present in high concentrations in cells of young fruits, leaves or seeds are responsible for the resistance of young tissues to Botrytis. In many host-pathogen combinations, as soon as the pathogen establishes contact with the cell, the nucleus moves toward the invading pathogen and soon disintegrates. Brown resin like granules form in the cytoplasm, first around the point of penetration of pathogen and then throughout the cytoplasm.
