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.

The impact of host plant (Pinus thunbergii) on the mycelial features of the ectomycorrhizal fungus Rhizopogon roseolus.

The impact of host plant on the mycelial features of mycorrhizal symbiont and its characteristics has been poorly investigated. This study aimed to compare and quantify (statistically tested) some of the mycelial features of an ectomycorrhiza (ECM)-forming fungus with and without the ECM host. The ECM-forming fungus, Rhizopogon roseolus, inoculated with or without Pinus thunbergii on both rich and poor nutrient media, was observed under laboratory conditions. On rich medium, fungi with the host had the highest colony diameter and consistently produced the highest hyphal length relative to fungi on other media. Thus, the host had a significant impact on the mycelium production of R. roseolus in both rich and poor media. Further, fungi without the host had a higher number of hyphal anastomoses per hyphal length on both poor and rich media than fungi with the host in the same medium. Anastomosis, which refers to the fusion of two parallel hyphae, was evident in all experiments. However, there was no significant impact of the host on the number of hyphal anastomoses. In addition, fungi without the host had more frequent hyphal branching on both rich and poor media than fungi with the host. The occurrence of a host only had a significant impact on the formation of the hyphal branch on poor medium. Further, a chlamydospore-like structure was identified, which had a higher diameter when formed with the host on both rich and poor media. The present data provide new insights into the host plant's impact on the mycelial features of ECM-forming fungi.

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

Most cytology reports on ectomycorrhiza (ECM) have been less focused on the fungal structures, especially on the exploratory organ. This study aimed to evaluate the morphological response of explorative mycelia of ECM forming fungi with and without the occurrence of the ECM host. We assessed the mycelial aggregates of Rhizopogon roseolus which was inoculated with and without Pinus thunbergii under controlled laboratory conditions. The mycelial aggregates with the host produced strikingly complex hyphal strands relative to those without host. Light microscopy revealed that the cytology and plectology of both mycelial aggregates had the approximately similar architecture. The tubular hyphae diameter without the host was consistently larger than that with the host. This study confirmed that the septa diameter of the tubular hyphae conjunction of mycelial aggregates with the host were shorter than those without the host. In addition, partially and completely dissolved septa of the tubular hyphae were evident with and without host. We also described the thromboplerous hyphae, which have rarely been reported in vitro. These hyphae were produced in higher numbers near the fungal inoculum with and without the host. The current findings will add to the current knowledge regarding ECM fungi mycelial aggregate response to the host.