Who discovered viroids?

In cyanophage,the genetic material is

$T. O.$ Diener discovered a new infectious agent that was smaller than viruses and has the following characteristics:
$(i)$ It causes potato spindle tuber disease.
$(ii)$ It has free $RNA$.
$(iii)$ The molecular weight of $RNA$ is low.
Identify the infectious agent.

What was the contribution of the scientist $T$. $O$. Diener in $1971$?

Tobacco Mosaic Virus $(TMV)$ genes are

Enzymes are absent in