Viruses consist of a nucleic acid core surrounded by a protein capsid with or without an outer lipid envelope. The capsid shape, presence of an envelope, and core composition dictate some elements of the classification of viruses.

Plant viruses may be transmitted either vertically from parent reproductive cells or horizontally through damaged plant tissues. Viruses are tiny, noncellular entities that usually can be seen only with an electron microscope.

productive — viral infection that leads to the production of new virions. envelope — lipid bilayer that encircles some viruses. capsid — protein coating of the viral core. asymptomatic disease — disease where there are no symptoms and the individual is unaware of being infected unless lab tests are performed.