Diener was born in 1921 in Zurich, Switzerland. He came to the United States in 1949. In 1971 he showed that the causative agent of Potato spindle tuber disease was the potato spindle tuber viroid (PSTV). PSTV is a 130,000 dalton viroid. Viroids are very little single-stranded circular RNA that have no coat protein, and which do not code for any protein.