Viroids

doi:10.1016/S0065-3527(08)60725-3

Advances in Virus Research

Volume 28, 1983, Pages 241-283

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This chapter discusses the recent developments in the viroid field. Viroids are low-molecular-weight RNAs of a unique previously unknown structure that are the causative agents of diseases, such as potato spindle tuber, citrus exocortis, chrysanthemum stunt, hop stunt, and tomato apical stunt. Unlike viral nucleic acids, viroids are not encapsidated; that is, no virion-like particles can be isolated from infected tissue. Although viroids have been discovered because of their propensity to cause readily recognizable disease symptoms in certain hosts, in certain other species viroids sometimes are replicated without causing obvious damage to the host. Recent results suggest that viroids may be more common in nature than previously believed and that they are not restricted to diseased plants. Still puzzling are the mechanisms by which a viroid may incite serious disease in some hosts yet replicate harmlessly in others. In this regard, some plausible and testable hypotheses are formulated and efforts to confirm or refute these speculative models will result in insights not only important for phytopathology and virology, but for plant physiology and molecular biology as well.

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