A viroid is a small, infectious agent that consists solely of a short strand of RNA. Unlike viruses, viroids do not have a protein coat and are much simpler in structure. They primarily infect plants, causing various diseases that can lead to significant agricultural losses. Viroids replicate within the host plant's cells, disrupting normal cellular functions. They are known to affect a range of plant species, including tomatoes and potatoes. Research on viroids helps scientists understand plant pathology and develop strategies for managing viroid-related diseases in crops.