The search for resistance to Heterobasidion root rot in Norway spruce - old and new approaches in studies of infection biology

The paper surveys the methods used for studying the root rot in Norway spruce (Picea abies) and summarizes the major results on Heterobasidion infection, the importance of the rhizosphere, preformed and induced resistance factors, search for trees with high resistance, and on virulence factors of the fungus. New approaches are discussed regarding where to look for resistance, how to study host-parasite interaction, the importance of stress factors, and the need for short-term experiments and standardized inoculum.