Hyaloscypha gabretae and Hyaloscypha gryndleri spp. nov. (Hyaloscyphaceae, Helotiales), two new mycobionts colonizing conifer, ericaceous and orchid roots

Historically, Hyaloscypha s. lat. (Hyaloscyphaceae, Helotiales) included various saprobes with small apothecia formed on decaying plant matter, usually wood, that were defined by chemical and (ultra)structural aspects. However, recent molecular phylogenetic and resynthesis studies have narrowed the concept of the genus and shown that it contains several widely distributed species with unknown sexual morphs that form ectomycorrhizae, ericoid mycorrhizae, and mycothalli and also grow endophytically in plant roots and hypogeous ectomycorrhizal (EcM) fruitbodies (i.e., the historical Hymenoscyphus ericae aggregate). Hence, some of the sexually reproducing saprobic Hyaloscypha s. lat. and the symbionts belong to the monophyletic Hyaloscypha s. str. Here, we introduce two new root-symbiotic Hyaloscypha s. str. species, i.e., H. gabretae and H. gryndleri spp. nov. While the former was isolated only from ericaceous hosts (Vaccinium myrtillus from Southern Bohemia, Czechia and Calluna vulgaris from England, UK), the latter was obtained from a basidiomycetous EcM root tip of Picea abies (Pinaceae), roots of Pseudorchis albida (Orchidaceae), and hair roots of V. myrtillus from Southern Bohemia and C. vulgaris from England. Hyaloscypha gryndleri comprises two closely related lineages, suggesting ongoing speciation, possibly connected with the root-symbiotic life-style. Fungal isolates from ericaceous roots with sequences similar to H. gabretae and H. gryndleri have been obtained in Japan and in Canada and Norway, respectively, suggesting a wide and scattered distribution across the Northern Hemisphere. In a series of in vitro experiments, both new species failed to form orchid mycorrhizal structures in roots of P. albida and H. gryndleri repeatedly formed what morphologically corresponds to the ericoid mycorrhizal (ErM) symbiosis in hair roots of V. myrtillus, whereas the ErM potential of H. gabretae remained unresolved. Our results highlight the symbiotic plasticity of root-associated hyaloscyphoid mycobionts as well as our limited knowledge of their diversity and distribution, warranting further ecophysiological and taxonomic research of these important and widespread fungi.

The root-symbiotic Rhizoscyphus ericae aggregate and Hyaloscypha (Leotiomycetes) are congeneric: Phylogenetic and experimental evidence

Data mining for a phylogenetic study including the prominent ericoid mycorrhizal fungus Rhizoscyphus ericae revealed nearly identical ITS sequences of the bryophilous Hyaloscypha hepaticicola suggesting they are conspecific. Additional genetic markers and a broader taxonomic sampling furthermore suggested that the sexual Hyaloscypha and the asexual Meliniomyces may be congeneric. In order to further elucidate these issues, type strains of all species traditionally treated as members of the Rhizoscyphus ericae aggregate (REA) and related taxa were subjected to phylogenetic analyses based on ITS, nrLSU, mtSSU, and rpb2 markers to produce comparable datasets while an in vitro re-synthesis experiment was conducted to examine the root-symbiotic potential of H. hepaticicola in the Ericaceae. Phylogenetic evidence demonstrates that sterile root-associated Meliniomyces, sexual Hyaloscypha and Rhizoscyphus, based on R. ericae, are indeed congeneric. To this monophylum also belongs the phialidic dematiaceous hyphomycetes Cadophora finlandica and Chloridium paucisporum. We provide a taxonomic revision of the REA; Meliniomyces and Rhizoscyphus are reduced to synonymy under Hyaloscypha. Pseudaegerita, typified by P. corticalis, an asexual morph of H. spiralis which is a core member of Hyaloscypha, is also transferred to the synonymy of the latter genus. Hyaloscypha melinii is introduced as a new root-symbiotic species from Central Europe. Cadophora finlandica and C. paucisporum are confirmed conspecific, and four new combinations in Hyaloscypha are proposed. Based on phylogenetic analyses, some sexually reproducing species can be attributed to their asexual counterparts for the first time whereas the majority is so far known only in the sexual or asexual state. Hyaloscypha bicolor sporulating in vitro is reported for the first time. Surprisingly, the mycological and mycorrhizal sides of the same coin have never been formally associated, mainly because the sexual and asexual morphs of these fungi have been studied in isolation by different research communities. Evaluating all these aspects allowed us to stabilize the taxonomy of a widespread and ecologically well-studied group of root-associated fungi and to link their various life-styles including saprobes, bryophilous fungi, root endophytes as well as fungi forming ericoid mycorrhizae and ectomycorrhizae.

From rhizoids to roots? Experimental evidence of mutualism between liverworts and ascomycete fungi

Background and Aims

The rhizoids of leafy liverworts (Jungermanniales, Marchantiophyta) are commonly colonized by the ascomycete fungus Pezoloma ericae. These associations are hypothesized to be functionally analogous to the ericoid mycorrhizas (ErMs) formed by P. ericae with the roots of Ericaceae plants in terms of bi-directional phosphorus for carbon exchange; however, this remains unproven. Here, we test whether associations between the leafy liverwort Cephalozia bicuspidata and P. ericae are mutualistic.

Methods

We measured movement of phosphorus and carbon between C. bicuspidata and P. ericae using [33P]orthophosphate and 14CO2 isotope tracers in monoxenic cultures. We also measured leafy liverwort growth, with and without P. ericae.

Key Results

We present the first demonstration of nutritionally mutualistic symbiosis between a non-vascular plant and an ErM-forming fungus, showing transfer of fungal-acquired P to the liverwort and of liverwort-fixed C to the fungus alongside increased growth in fungus-colonized liverworts.

Conclusions

Thus, this ascomycete-liverwort symbiosis can now be described as mycorrhiza-like, providing further insights into ericoid mycorrhizal evolution and adding Ascomycota fungi to mycorrhizal fungal groups engaging in mutualisms with plants across the land plant phylogeny. As P. ericae also colonizes the rhizoids of Schistochilaceae liverworts, which originated in the Triassic and are sister to all other jungermannialean liverworts associated with fungi, our findings point toward an early origin of ascomycete-liverwort symbioses, possibly pre-dating their evolution in the Ericales by some 150 million years.

First record of Rhizoscyphus ericae in Southern Hemisphere's Ericaceae

Ericoid mycorrhiza is arguably the least investigated mycorrhizal type, particularly when related to the number of potential hosts and the ecosystems they inhabit. Little is known about the global distribution of ericoid mycorrhizal (ErM) fungi, and this holds true even for the prominent ErM mycobiont Rhizoscyphus ericae. Earlier studies suggested R. ericae might be low in abundance or absent in the roots of Southern Hemisphere's Ericaceae, and our previous investigations in two Argentine Patagonian forests supported this view. Here, we revisited the formerly investigated area, albeit at a higher altitude, and screened fungi inhabiting hair roots of Gaultheria caespitosa and Gaultheria pumila at a treeless alpine site using the same methods as previously. We obtained 234 isolates, most of them belonging to Ascomycota. In contrast to previous findings, however, among 37 detected operational taxonomic units (OTUs), OTU 1 (=R. ericae s. str.) comprised the highest number of isolates (87, ∼37 %). Most of the OTUs and isolates belonged to the Helotiales, and 82.5 % of isolates belonged to OTUs shared between both Gaultheria species. At the alpine site, ericoid mycorrhizal fungi dominated, followed by dark septate endophytes and aquatic hyphomycetes probably acting as root endophytes. Our results suggest that the distribution of R. ericae is influenced, among others, by factors related to altitude such as soil type and presence/absence and type of the neighboring vegetation. Our study is the first report on R. ericae colonizing Ericaceae roots in the Southern Hemisphere and extends the known range of this prominent ErM species to NW Patagonia.