STRUCTURE AND PHYSIOLOGY OF ECTOMYCORRHIZAE

Abstract

SUMMARY The process of mycorrhiza formation in previously uninfected roots was studied in vitro , using the fungus Piloderma croceum Erikss. & Hjortst, and the Norway spruce, Picea abies (L.) Karst, as model organisms. The process could be divided into the following phases: fungal growth stimulation by root metabolites; formation of a hyphal envelope on the root; intercellular penetration by single hyphae, change in fungal morphology into labyrinthic tissue formation leading to Hartig net formation, and extension of labyrinthic tissue to form a mantle. P. croceum , growing in dead tissue, showed saprophytic growth in vitro , a capacity suppressed in living tissue. The way of fungal penetration appeared to be mechanical. A hypothetical model for host‐fungus interactions regulating the mycorrhiza infection process is also discussed.