Viroids were discovered by T.O. Diener in the year 1971.
They are smaller in size than viruses.
They do not possess a protein coat.
They have free, single-stranded circular RNA as their genetic material.
After the replication, newly formed viroid exit the nucleus or chloroplast and move to adjacent cells via plasmodesmata, and can travel systemically via the phloem to infect other cells.
Viroids then enter the pollen and ovule, from where they are transmitted to the seed. When the seed germinates, the new plant becomes infected.
