a plant pathogen composed of molecules of naked RNA only several hundred nucleotides long.
The viroid responsible for cucumber pale fruit viroid (CPFV) infection in cucumbers is called the cucumber pale fruit viroid (CPFV). This viroid can cause symptoms such as yellowing, stunting, and distortion of leaves in infected plants.
A prion or proteinacious infections particle is simply a protein. They exist as normal proteins in our brain termed PrP, however in certain ecepalopathy diseases these prions are thought to alter shape to a more resistant tertiary protein structure (more beta pleated sheets than alpha helices) and are termed PrPsc. It is theorised the PrPsc are able to convert normal prions to pathogenic ones. Mode of transmission between organisms is unknown as the blood brain barrier should prevent them from getting to the brain of the infected organism. A viriod however is a naked strand of DNA/RNA that causes disease mainly in plants. It does this by cell infection, and then expression of its own genetic code, hijacking the cellular protein synthesis apparatus of the cell to copy itself.