ABSTRACT
Viruses enter their hosts through one or more of the following ways: mechanical inoculation through abrasion, and introduction through vectors, dodder, or graft union. Entry is through the epidermis in the case of mechanical inoculation and chiefly by nonpersistent transmission through vectors. Cell-to-cell transport occurs between parenchyma cells and between parenchyma and vascular tissue. Most of the plant viruses as well as their nucleic acid and coat protein are macromolecules of sizes too large to pass freely through the desmotubule of a normal plasmodesma. Systemic spread of a virus within a host is the result of long-distance transport of virus through phloem tissue. Long-distance movement starts once the viral infection leaves the parenchyma and enters the phloem tissue. The rate of transport of some viruses is intermediate between the slow cell-to-cell transport and the rapid long-distance transport.
