T.O. Diener discovered a:

Explanation

1. Free infectious DNA-Avery, MacLeod, and McCarty (1944) indeed demonstrated that DNA is the "transforming principle," proving it carries genetic information. This was a landmark in molecular genetics. 2. Infectious protein (prion)-Stanley Prusiner (1982, Nobel Prize in 1997) introduced the term "prion" and demonstrated that certain diseases are caused by protein-only infectious agents. 3. Bacteriophage - Frederick Twort (1915) first observed a "filterable agent" that killed bacteria, and Félix d'Hérelle (1917) independently discovered and named bacteriophage. 4. Free infectious RNA-This concept is best represented by viroids (discovered by Theodor Diener in 1971), which are small circular RNAs that infect plants. Some RNA viruses also highlight RNA as infectious material, but unlike DNA, there wasn't a single definitive early experiment attributed to just RNA.