Cytological comparison of mycelial aggregates of Rhizopogon roseolus with and without the ectomycorrhiza host

Hyphal coil morphology and its relationship to thromboplerous hyphae in Rhizopogon roseolus

While observing mycelial features of the ectomycorrhizal fungus Rhizopogon roseolus, we noted the formation of hyphal coils in laboratory cultures. The coiled hyphae initially formed at the hyphal tip in the presence or absence of the plant host (Pinus thunbergii), on both rich and poor modified Melin-Norkrans media. Hyphal coils formed from the hyphal tips toward the middle of the hyphae, with rope-like hyphal strands fused as extensive circular coils. Hyphal coils were generally oval and circular. Coils were composed of 1-5 layers of hyphae. Presence of the host had a significant impact on the diameter of the coil loops, which was consistently wider without the host than with the host present on both media. In addition, the terminal part of the mature coils was melanized and separated from the unmelanized coil by a septum. The melanized coils resembled thick condensed hyphae and were detached and scattered throughout the fungal colony. The observation of morphological characteristics suggested that mature coils detached into the mycelia were thromboplerous hyphae. This is the first report on hyphal coil morphogenesis and its potential relationship to the initial development of thromboplerous hyphae.

Basidium formation of Rhizopogon roseolus with Pinus thunbergii in agar medium

The edible ectomycorrhizal (ECM) mushroom Rhizopogon roseolus usually develops basidium and basidiospores in the gleba of its basidiomata. Here, we report a novel production of basidia in laboratory cultures of the edible ECM mushroom. The basidium with sterigma was observed on the old mantle structure (> six months) of the ECM between R. roseolus and Pinus thunbergii in a modified Melin-Norkrans medium that was subjected to a temperature shock from 25 °C to 4 °C. The basidia were cylindrical to clavate, with prominent sterigmata and no basidiospores. The absence of basidiospores might indicate partial development of the basidium structure as a response to environmental stress and incomplete life cycle of R. roseolus. In addition, branched cystidia were evident in two or three clavate-to-ovoid cells. This study suggests the possibility of obtaining the primary mycelium of R. roseolus from pure cultures and may be an alternative genetic source for cultivation purposes. Further observations are required to induce basidiosporogenesis of R. roseolus basidia in an agar medium focusing on manipulation of temperature.