# Theodor Otto Diener

Theodor Otto Diener (28 February 1921 – 28 March 2023) was a Swiss-American plant pathologist. In 1971, he discovered that the causative agent of the potato spindle tuber disease is not a virus, but a novel agent, which consists solely of a short strand of single-stranded RNA without a protein capsid, eighty times smaller than the smallest viruses. He proposed to name it, and similar agents yet to be discovered, viroids. Viroids displaced viruses as the smallest known infectious agents.

## Biography

Diener was born in Zürich, Switzerland on 28 February 1921. He attended the Swiss Federal Institute of Technology, from which he graduated with a Dr.sc.nat.ETH degree in 1946. After graduation, he worked as a research assistant at the Swiss Federal Experiment Station for Viticulture and Horticulture at Wädenswil, where he discovered on leaves of a cherry tree the first occurrence in more than 100 years of a rust fungus (Puccinia cerasi), a fungus which is common south of the Alps, but is rarely seen in the north.
In 1949, he emigrated to the United States, where, after a brief tenure at the Rhode Island State College, he accepted a position as assistant plant pathologist at Washington State University's outlying Irrigation Experiment Station in Prosser, where he showed that an unusual amino acid, pipecolic acid, accumulates only in peach leaves bearing symptoms of Western-X-Disease. and that injection of the amino acid into healthy peach seedlings resulted in abnormalities which strikingly resembled disease symptoms, thus indicating that pipecolic acid is intimately associated with the disease's molecular pathogenesis.
In 1959, Diener joined the US Department of Agriculture's Agricultural Research Service Pioneering Laboratory for Plant Virology at the Agricultural Research Center in Beltsville, Maryland, where he investigated the cause of the potato spindle tuber disease. This led to the unexpected discovery of the causative agent, a small RNA molecule, eighty times smaller than the smallest known viruses, for which he proposed the term viroid. Later, viroids were characterized as single stranded covalently closed circular RNA molecules occurring as highly base-paired rod-like structures. Viroids, together with viroid-like satellite RNAs have been officially endorsed by the International Committee for Virus Taxonomy (ICTV) as a novel order of subviral agents, which, in its 2014 publication, encompassed 2 families, 8 genera and 32 species.
In 1989, Diener hypothesized that the unique properties of viroids make them more plausible candidates as "living relics" of a hypothetical, pre-cellular RNA world than are Introns or other RNAs then considered as such. In 2016, Diener reevaluated his hypothesis, with the result that both reviewers agreed that Diener's hypothesis was still valid, but that alternative hypotheses positing a more recent origin of viroids from cellular RNAs needed also to be considered.
Diener had three sons with his first wife, Shirley Baumann, before they divorced. He was then married to Sybil Fox from 1968 until her death in 2012. Diener died at his home in Beltsville, Maryland on 28 March 2023, at the age of 102.
Diener published 2 books on viroids, 120 peer-reviewed articles, 53 chapters in books, and lectured on viroids worldwide

### Awards and honors

* 1968: Campbell Award, American Institute of Biological Sciences
* 1969: Superior Service Award, U.S. Department of Agriculture
* 1973: Fellow Award; American Phytopathological Society
* 1975: Alexander von Humboldt Award, Alexander von Humboldt Society
* 1976: Ruth Allen Award: American Phytopathological Society
* 1977: Elected Member; U.S. National Academy of Sciences
* 1978: Elected Fellow, American Academy of Arts and Sciences
* 1979: Elected Andrew D. White Professor-at-Large, Cornell University
* 1980: Elected member, Leopoldina, German Academy of Sciences
* 1987: Wolf Prize in Agriculture, Wolf Foundation/State of Israel
* 1987: National Medal of Science, USA
* 1988: E.C. Stakman Award, University of Minnesota
* 1988: Distinguished Service Award, Potomac Division, American Phytopathological Society
* 1989: Inducted into Science Hall of Fame, Agricultural Research Service, U.S. Department of Agriculture
* 1989: Named Distinguished Professor, University of Maryland, College Park, MD
* 1994: Named Distinguished Professor Emeritus, University of Maryland, College Park, MD