Viroids:
1. These are mainly plant pathogens.
2. Viroids were discovered by Theodor Diener.
3. The first viroid discovered was PSTV (Potato spindle tuber viroid) which causes a disease in potato.
4. Viroids are very small, circular, single stranded RNA which are without any protein coat.
5. Viroids are smaller in size than viruses.
