Who discovered infectious agents even smaller than virus with only nucleic acid and no protein coat?
The correct option is D T.O. Diener
T.O. Diener (1971) discovered some new infections agents, which are smaller than viruses. These sub-viral infections agents are called viroids. Viroids contain only very low molecular weight RNA and lack protein coat. Viroids cause potato spindle tuber disease (PSTV), Chrysanthemum stunt, Citrus exocortis, cucumber pale fruit etc.