ABSTRACT
In several host-parasite systems, death or cessation of the pathogen's growth have been reported to precede hypersensitive host cell death and accumulation of inhibitory compounds. As already mentioned recognition between host and parasite as an incompatible or compatible partner, is a key factor which determines outcome of host-parasite interaction particularly in biotrophic infections. Taxonomically distantly related organisms, higher plant and bacteria or fungi, has been demonstrated in several host-parasite systems. In certain host-parasite systems fungal cell death precedes host cell death, indicating that at least in such cases necrosis of host cell may be consequence rather than cause of resistance. Once an organism is recognized at the level of surface-to-surface interaction as incompatible or "nonself", the plant's metabolism is activated resulting in the formation of toxic substances. Mere surface-to-surface interaction of the plant host and parasite might restrict the latter's activity. Interaction between a plant and a parasite commences even before their direct contact.
