1) Plant virus 2) The smallest of viruses 3) Viroid 1) Viroid 
Virusoids are circular single-stranded RNAs dependent on plant viruses for replication and encapsidation. The genome of virusoids consist of several hundred nucleotides and does not code for any proteins. Virusoids are similar to viroids in size, structure and means of replication (Rolling circle replication). Virusoids, while being studied in vir...
<molecular biology, virology> A type of small (300-400 nucleotides) single-stranded RNA found in the virions of some plant viruses. ... (09 Oct 1997) ... 
Type: Term Pronunciation: vī′rŭs-oyd Definitions: 1. A plant pathogen resembling a viroid but having a much larger circular or linear RNA segment and a capsid; it is a satellite agent requiring an associated virus (helper virus) for replication.
small piece of RNA associated with larger RNA of some infectious plant viruses