viroid

viroid, microscopic infectious agent, much smaller than a virus, that infects higher plants such as potatoes, tomatoes, chrysanthemums, and cucumbers, causing stunted or distorted growth and sometimes death. It can be transmitted by pollen, seed, or farm implements. Viroids are single strands of RNA and lack the protein coat of viruses. They do not code for any specific protein but are able to replicate themselves in the nuclei of infected cells. Some scientists believe viroids are parts of normal RNA that have gone awry. Potato spindle tuber viroid was the first to be identified.

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viroid

Infectious particle that is smaller than any of the known viruses. The particle consists of an extremely small circular RNA molecule that lacks the protein coat of a virus. Viroids appear to be transmitted mechanically from one cell to another through cellular debris. They are of much interest because of their subviral nature and their unknown mode of action. Viroids are agents of certain plant diseases; whether they occur in animal cells is uncertain.

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viroid [′vī‚rȯid]

(microbiology)

The smallest known agents of infectious disease, characterized by the absence of encapsidated proteins.