Armillaria mellea
Korhonen graduated as a biologist from the University of Helsinki in 1968. He made his career as a researcher at the Finnish Forest Research Institute in Helsinki, beginning in 1973. From the start his research concentrated on the forest pathogen fungi then known as "Heterobasidion annosum" and "Armillaria mellea". During his career over 40 years he collected more than 4000 isolates of these species in Scandinavia, Germany, Italy, Greece, USA, Canada, Estonia, Belarus, Siberia and China.