A COMPARATIVE-STUDY OF THE EFFECTS OF THE ROOT ENDOPHYTES LEPTODONTIDIUM-ORCHIDICOLA AND PHIALOCEPHALA-FORTINII (FUNGI IMPERFECTI) ON THE GROWTH OF SOME SUB-ALPINE PLANTS IN CULTURE

Resynthesis studies were done to determine the ecological role of Lept odontidium orchidicola, a dematiaceous hyphomycete commonly associated with roots of plants growing in cool and humus-rich soils. Results we re compared with those of Phialocephala fortinii, another common root endophyte with similar cultural and vegetative characteristics. In axe nic culture with Salix glauca seedlings, L. orchidicola caused a marke d increase in host root length but also invaded the stele, causing ext ensive cellular lysis. Phialocephala fortinii formed a Hartig net and a thin, patchy mantle. In pot monocultures with Potentilla fruticosa, Dryas octopetala, S. glauca, and Picea glauca seedlings, the effects o f four L. orchidicola strains on host dry weight were strain- and host -specific; the effects of Phialocephala fortinii were also host-specif ic. Leptodontidium orchidicola formed a range of symbiotic association s that could be considered mycorrhizal to parasitic, whereas the effec ts of Phialocephala fortinii suggest amensal, parasitic, or neutral as sociation. In pot combination cultures, the Phialocephala fortinii - P otentilla fruticosa symbiosis resulted in a significant increase in sh oot weight in contrast with the results of the same symbiosis in monoc ulture resynthesis. The resynthesis experiments demonstrated that the effects of both L. orchidicola and Phialocephala fortinii also vary ac cording to cultural conditions.