A comparative study of the effects of the root endophytes Leptodontidium orchidicola and Phialocephala fortinii (Fungi Imperfecti) on the growth of some subalpine plants in culture

Resynthesis studies were done to determine the ecological role of Leptodontidium orchidicola, a dematiaceous hyphomycete commonly associated with roots of plants growing in cool and humus-rich soils. Results were compared with those of Phialocephala fortinii, another common root endophyte with similar cultural and vegetative characteristics. In axenic culture with Salix glauca seedlings, L. orchidicola caused a marked increase in host root length but also invaded the stele, causing extensive 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 of four L. orchidicola strains on host dry weight were strain- and host-specific; the effects of Phialocephala fortinii were also host-specific. Leptodontidium orchidicola formed a range of symbiotic associations that could be considered mycorrhizal to parasitic, whereas the effects of Phialocephala fortinii suggest amensal, parasitic, or neutral association. In pot combination cultures, the Phialocephala fortinii - Potentilla fruticosa symbiosis resulted in a significant increase in shoot weight in contrast with the results of the same symbiosis in monoculture resynthesis. The resynthesis experiments demonstrated that the effects of both L. orchidicola and Phialocephala fortinii also vary according to cultural conditions.