Discovery of Viroids

For decades viruses were considered the smallest biological entity, a paradigm remaining undisputed until the discovery of viroids. Viroids were discovered by plant pathologist Dr. Theodor Diener and colleagues in 1971 while they were studying the potato spindle tuber disease.

They began intensive studies in 1963 on a transmissible disease of potato, spindle tuber, all infectious diseases of plants and animals were believe to be caused either by microorganisms or by virus and viruses were universally accepted as the smallest possible agents of such diseases.

Diener expected to find a viral pathogen, but was forced to consider other options after discovering that the infections agent passed through filters too fine to allow passage or even the smallest virus.

The particle, which Dr. Diener has called a ‘viroid’ is a fragment of RNA but does not have a protein coat similar to the of a virus, but is capable of invading the cells and disrupting their functions in the same manner a virus does.

More than 20 viroids have been described infecting a wide variety of plant species,. Many of these have great agricultural significance and are known to destroy fields of economically important crops.
Discovery of Viroids