Viroids


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Viroids

The smallest known agents of infectious disease. Conventional viruses are made up of nucleic acid encapsulated in protein (capsid), whereas viroids are uniquely characterized by the absence of a capsid. In spite of their small size, viroid ribonucleic acids (RNAs) can replicate and produce characteristic disease syndromes when introduced into cells. Viroids thus far identified are associated with plants.

Nine different viroids have been described from widely separated geographical locations and from an assortment of herbaceous and woody plants. Viroid infections in some plant species produce profound disease symptoms ranging from stunting and leaf epinasty to plant death, whereas infections in other species produce few detectable symptoms compared to uninoculated control plants. Viroids generally have a restricted host range, although several viroids can infect the same hosts and cause similar symptoms in these hosts. Good controls are not available for diseases caused by these small infectious agents other than indexing procedures to provide viroid-free propagules. See Plant viruses and viroids, Virus

References in periodicals archive ?
Se conoce que los viroides y el transcripto correspondiente a un ARNm para una proteina endogena son ARNs moviles en el floema de plantas (Ding et al., 1997; Kim et al., 2001).
(3-5) There was an increase in free RNA indicating self replicating RNA viroids and free DNA indicating generation of viroid complementary DNA strands by archaeal reverse transcriptase activity.
Viroids resemble viruses, but consist of only small RNA molecules that do not have the protein coat found on viruses and that do not encode any proteins.
Finally, there is the possibility that "some viruses evolved from viroids or virusoids, although it is equally possible that these small RNA, rather than being progenitors of viruses, are recent degenerative products of the more complex self-replicating systems" (p.
Pollen- and seed-transmitted viruses and viroids. Annu.
Cellular machinery is so friendly toward DNA duplication that it is small wonder cells play host to DNA parasites--viruses, viroids, plasmids, and a riff-raff of other genetic fellow travelers.
Viroids are the smallest infectious particles know, consisting solely of naked RNA.
Organisms that cause infectious disease include fungi, oomycetes, bacteria, viruses, viroids, virus-like organisms, phytoplasmas, protozoa, nematodes and parasitic plants.
The loss, removal or damage of traditional plant labels at any stage of production can result in a mother plant that has no known history, which is especially problematic because of the many viruses, viroids, phytoplasmas and other systemic pathogens that can infect propagative material.
Actinides like rutile as well as organisms like phytoplasmas and viroids have been implicated in the etiology of EMF [1,2,3,4].