Disease Facts Cooperative Extension - The Pennsylvania State University Virus Diseases Gary W. Moorman Plant Pathologist Viruses are submicroscopic entities capable of causing disease. Once inside the plant cell, the nucleic acid portion directs the plant cell to produce more virus nucleic acid and virus protein, disrupting the normal activity of the cell. Viruses can multiply only inside a living cell. While some viruses, such as cucumber mosaic, die quickly if outside a cell or if the cell dies, other viruses such as tobacco mosaic retain their ability to infect for years after the infected plant part dies.
Many different viruses can infect plants.
Depending on which virus is involved, the disease may be spread from infected plants to healthy plants . . . Cuttings taken from an infected plant usually are infected even if no symptoms are immediately exhibited by the cutting. The virus particles are found in all parts of the plant except the few cells at the tips of the growing points. It is these few cells that are removed and grown into a healthy plant free of virus by the process called meristem tip culturing. Symptoms vary with the virus involved, the species of plant infected, and the environmental conditions.