ABSTRACT
Viruses are small intracellular parasites, the biological activity of which is confined to the inside of the host cells. They are parasites conveyed from one host plant to another. Once a virus is introduced into a plant cell, by mechanical penetration, performed by a biological agent or by physical mechanism, it is capable of using the cellular machinery and to replicate. Following intracellular replication, viruses spread to neighboring cells by cytoplasmatic connections between cells, the plasmodesmata, and spread to long distances within the host, through the vascular system. An understanding of the natural response of host plants in limiting viral damage and avoiding the collapse of the host may help the development of viral tolerance in crops. This chapter discusses plant virus infestation from the host adaptive point of view, and examines the mutual existence of virus-host, without the elimination of one by the other.
