STUDIES ON THE MYCORRHIZAS OF PINU SYLVESTRIS L. PRODUCED IN VITRO WITH THE BASIDIOMYCETE SUILLUS VARIEGATUS (SW. ex Fr.) O. KUNTZE

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Abstract
Summary: Ectomycorrhizas of Pinus sylvestris L. synthesized in vitro with Suillus variegatus (Sw. EX Fr.) O. Kuntze were studied by light and electron microscopy. Approximately two months following innoculation of germinated seedlings of Pinus sylvestris with the fungus, the host showed well‐developed ectomycorrhizas each consisting of a fungal mantle, tannin layer and Hartig net region surrounding the endodermis and root vascular cylinder. The mantle formed by the mycosymbiont was 3 to 10 hyphae deep and covered the root tip completely but did not invade the cells of the apical meristem. The tannin layer consisted of dead host cells, apparently derivatives of the root cap, containing electron‐dense deposits. Fungal cells which did not differ in appearance from those forming the mantle and the Hartig net were appressed to the tannin layer, partly embedded in an electron‐dense mucilaginous substance. The fungal hyphae in the Hartig net region were up to several cells in thickness but did not penetrate the protoplasts of the root cortex cells nor the intercellular spaces beyond the endodermis. The presence of plasmodesmata in the cell walls not separated by the fungal hyphae indicated that symplastic continuity of the root cells in the Hartig net region was not completely disrupted. The ultrastructure of the various cells of the mycorrhizas plus examination of free‐hand sections indicate that the mycorrhizas, at the time of fixation, were viable associations. The structure of the mycorrhizas produced in vitro is compared and discussed with respect to naturally occurring mycorrhizas on the same host species.