Viroids are infectious entities that affect plants which are smaller compared to a virus. They consist of only the nucleic acid without a protein coat. Viruses are an infective agent consisting of a nucleic acid molecule in a protein coat
Viroids are different from viruses in the following ways:
- Its RNA does not code for protein
- It exists within the cells as RNA particles only with no envelope or capsid
- It possesses only one circular RNA strand comprising of very few nucleotides
- Contrary to viruses, viroids require no help of viruses to infect cells
- Contrary to viruses of which the RNA can be copied in the nucleus or cytoplasm, the RNA of viroids are copied in the nucleus only
- To detect the presence of viroids in the plant tissues, special techniques are used
