Formation and Structure of Mycorrhizas of Seedlings of Coachwood (Ceratopetalum apetalum)

The mycorrhizas of seedlings of coachwood (Ceratopetalum apetalum) were examined. When the host was grown under increased photon flux density infections of both vesicular-arbuscular (VA) and a sheathing association were extended. Paris type VA mycorrhizas were observed, though arbuscules and vesicles were rare. Hyphae of VA mycorrhizal fungi appeared to degenerate when under the sheathing association. The sheathing association was characterised by thin mantles and no Hartig net. An electron-dense bilayer formed over hyphae in the sheath and hyphae were surrounded by a fibrillar matrix. Beneath the sheath, the walls of the epidermis were thickened and fibrillar. Lignin and suberin were present in the walls of cells of the hypodermis and absent in the epidermis. No evidence was found that the fungal associations induced a negative response from the host. While the structure of the mycorrhizas was unusual, the sheathing association was believed to be a variant of typical ectomycorrhizas.