His son, Michael Diener, confirmed his death but did not give a cause of death.
Dr. Diener immigrated to the United States in 1949 and spent 30 years as a plant pathologist at the Agricultural Research Service, a major internal research agency of the US Department of Agriculture.
President Ronald Reagan awarded him the National Medal of Science in 1971 for his identification of viroids. This achievement has been compared to his discoveries of bacteria in the late 1600s and viruses just before the turn of his twentieth century.
Since about the 1920s, farmers have known about confounding diseases that threaten potatoes. The disease shriveled and malformed the potatoes, causing him to reduce crop size by more than 50%. From the 1960s to the 1970s, According to a Forbes magazine report, In parts of China and Ukraine, half of the potatoes were diseased.
The condition was given the name potato spindle tuber disease, but its cause turned out to be embarrassingly elusive.
Dr. Diener is known for working with his ARS colleagues for years to identify the infectious agent at the root of the proverbial problem. Using research methods that included centrifugation, he determined that the culprit was not a virus, as other scientists had speculated, but a new, much smaller pathogen, a viroid.
Viroids function similarly to viruses, entering cells and replicating their viroid RNA. Unlike viruses, viroids do not have a protein coat. According to ARSthe long-standing consensus among scientists was that such “naked” pathogens cannot replicate, even with the help of infected cells.
Most scientists also believed that very small pathogens, such as those discovered by Dr. Diener, could not enter living organisms. But Dr. Diener’s work has proven that viroids so small that they are barely visible even under an electron microscope can actually mount an effective attack.
After identifying the viroid, Dr. Diener helped develop a test to detect the viroid that causes potato spindle tuber disease. Viroids were later found to cause symptoms such as fading dwarfs in tomatoes, scars in apples, sunburn in avocados, and stunting in chrysanthemums.
Dr. Diener national science awardwas awarded in 1987.
Theodor Otto Diener was born on February 28, 1921 in Zurich, German-speaking Switzerland. His father was a postal worker and his mother an accountant. From a young age, the future scientist was drawn to plants and animals.
“When I was a boy, I always had animals at home: turtles, salamanders, frogs, white rats, hamsters,” he once told an interviewer. “My parents showed considerable tolerance for this, but my neighbors often didn’t.”
After saving enough money to buy a used Leitz microscope, he said, his curiosity led him to even smaller creatures.
Dr. Diener studied biology at the Swiss Federal Institute of Technology and received his doctorate in 1948.
After immigrating to the United States and becoming a naturalized U.S. citizen, he worked as a plant pathologist at Washington State University before joining ARS in Beltsville in 1959. Long after his official retirement in 1988, he collaborated on ARS research.
He also researched and taught at the University of Maryland, where he was an emeritus professor.
In addition to the National Medal of Science, Dr. Diener’s accolades include election to the National Academy of Sciences in 1977 and the American Academy of Arts and Sciences in 1978. Wolf Foundation of Israel.
In addition to his prolific scientific publications, he has written two books, “Viroids and Viroid Diseases” (1979) and a memoir, “Of Humans, Humanoids and Viroids” (2014).
Dr. Diener’s marriage to Shirley Baumann ended in divorce. The former wife of Sybil Fox, with whom she was married for 44 years, died in 2012.
Survivors include three sons from his first marriage, Theodore Diener of Los Angeles, Robert Diener of Urbana, Illinois, and Michael Diener of Vienna, Virginia. five grandchildren; and three great-grandchildren.
As with many scientific advances, Dr. Diener’s discovery of viroids was the result of many previous successful attempts.Reflecting on his efforts towards deciphering potato tuber disease, he sarcastically told the New York Times“We went up the garden path many times.”
