Theodor O. Diener

Theodor O. DienerInducted in 2007 for his pioneering work in plant pathology has enabled the control of viroid diseases of many crops.

Theodor Otto Diener took the scientific world by surprise in 1971 when he discovered the viroid, a plant pathogen one fiftieth of the size of the smallest viruses. These tiny single-stranded RNA molecules were responsible for causing a devastating disease of potato plants, called potato spindle tuber disease, as well as at least 15 other crop diseases. Diener’s breakthrough was in discovering this organism, which had previously been assumed to be a virus because it invaded cells and hijacked their reproductive mechanisms, but that was clearly not a virus because it wasn’t structured like one. Diener named it the “viroid,” because it is “like a virus.”

Like a virus, the viroid invades a cell and hijacks its reproductive mechanisms. It forces the cell to duplicate the viroid's RNA instead of its own. The viroid has no DNA. RNA and DNA are nucleic acids, the molecules of heredity; with the exception of viroids and some viruses, all genes are made of DNA. The difference between viroids and RNA viruses is that viroids have no protective protein coat. The scientific dogma in 1971 was that an organism with no protein wasn't supposed to be able to replicate itself, even with a host cell's help. And an entity as small as the PSTV (potato spindle tuber viroid)—130,000 daltons—wasn't supposed to be able to infect anything, even a potato.

Until that time, scientists believed that the minimum weight necessary for infectivity was about 1 million daltons. (A dalton, also called an atomic mass unit, equals one-twelfth the mass of a carbon-12 atom.) But Diener persevered despite his colleagues’ doubts and proved that the viroid really existed. In all, it took him six painstaking years. Diener’s discovery revolutionized the study, diagnosis, and treatment of viral plant diseases. It also helped change approaches and attitudes in the study of livestock and human diseases.

Diener is Distinguished University Professor Emeritus at the University of Maryland. He obtained a Dr. sc. nat. ETH degree from the Swiss Federal Institute of Technology, Zürich, and was an Associate Professor of Plant Pathology at Washington State University, USA, and Research Plant Pathologist at the Pioneering Laboratory for Plant Virology, US Department of Agriculture, Beltsville, USA. Professor Diener has been honored with numerous awards, among them the US National Medal of Science, the Wolf Prize in Agriculture, the Alexander-von-Humboldt Award, and the US Department of Agriculture Distinguished Service Award. He is a member of the National Academy of Sciences, the American Academy of Arts and Sciences, and the German Academy of Natural Scientists, Leopoldina.