Naked infectious RNA molecules that lack a protein coat and cause diseases of plants are called

Explanation

Viroids are short circular RNA molecules with no capsid at all, and they cause plant diseases such as potato spindle tuber disease. The word prion is the tempting confusion because both are sub viral agents, but a prion is the opposite case: infectious protein with no nucleic acid. A bacteriophage is a complete virus with a capsid and a tail.