The type of the in vitro root interactions of Terfezia terfezioides with the plants Robinia pseudoacacia and Helianthemum ovatum was investigated including detailed anatomical and ultrastructural characterization. No difference in growth was detected at different phosphate concentrations on agar synthetic medium between the inoculated and control plants during a short-time cultivation. The fungal colonization of the roots increased with higher phosphate level in both plant species, but was always lower in R. pseudoacacia roots. Septate hyphae formed frequently intracellular branched coils in dead cortical cells. In H. ovatum intercellular hyphae were observed forming finger-like structures reminiscent of Hartig-net structures in ectomycorrhizae. A loose hyphal envelope covered the root surface of both colonized and noncolonized roots. The features resembled similar structures described earlier during the mycorrhizae of different Terfezia species. Our detailed anatomical and ultrastructural study shows that the in vitro root interactions of the T. terfezioides cannot be considered unambiguously as mycorrhiza.
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