Isolation of Oidiodendron maius from Rhododendron and ultrastructural characterization of synthesized mycorrhizas

Abstract

Twelve fungal isolates were obtained from roots of field-grown Rhododendron plants. One of these produced ericoid mycorrhizal roots within 5 days when reassociated with Rhododendron plantlets under aseptic conditions. The organism was identified as Oidiodendron maius. A characteristic feature of this organism was production of conidiophores in both pure culture and in association with root cells of the host. Ultrastructural observations confirmed its mycorrhizal status and showed intracellular hyphae surrounded by an interfacial zone and plasma membrane. Hyphae were found in close association with the host nucleus and cytoplasmic organelles. Pure isolates derived from diverse alternative sources were also tested for mycorrhizal formation with Rhododendron under aseptic conditions. Thus, Pezizella ericae obtained from Calluna vulgaris produced mycorrhizal infections after 10 days of culture, whereas O. maius from Sitka spruce and Oidiodendron griseum from wood pulp failed to form mycorrhizas.