The Movement of Viruses in Plants

Abstract

The full expression of thc effects of a plant virus in a susceptible host is dependent upon the virus spreading to most, if not all, parts of that host. It is generally accepted that most plant viruses enter the initially infected cells of a plant through mechanical damage inflicted by a biological vector (e.g. arthro­ pod, nematode, fungus etc) or by mechanical abrasion (e. g. breaking of leaf hair). From the initially infected cell there are two forms of spread within the plant, namely short-distance and long-distance. Short-distance spread is from one cell to an adjacent cell. whereas long-distance spread is in the vascular system. For many viruses, particularly those causing mosaics, both forms of spread occur; cell-to-cell from the initially infected epidermal or mesophyll cell to the vascular bundle and long-distance to other parts of the plant followed by further short-distance spread. Other viruses may be limited to the vascular tissue, usually phloem, where they are introduced by their vector(s). There are, of course, intermediate situations; some viruses, such as BYVI spread in a limited manner from the phloem.