Franz Oberwinkler

Sebacinales: a hitherto overlooked cosm of heterobasidiomycetes with a broad mycorrhizal potential*

Within the basidiomycetes, the vast majority of known mycorrhizal species are homobasidiomycetes. It was therefore surprising when molecular and ultrastructural studies revealed a broad diversity of mycorrhizal associations involving members of the heterobasidiomycetous Sebacinaceae, fungi which, due to their inconspicuous basidiomes, have been often overlooked. To investigate the phylogenetic position of the Sebacinaceae within the basidiomycetes and to infer phylogenetic relationships within the Sebacinaceae, we made molecular phylogenetic analyses based on nuclear rDNA. We present a well-resolved phylogeny of the main lineages of basidiomycetes which suggests that the Sebacinaceae is the most basal group with known mycorrhizal members. Since more basal taxa of basidiomycetes consist of predominantly mycoparasitic and phytoparasitic fungi, it seems possible that a mycorrhizal life strategy, which was transformed into a saprotrophic strategy several times convergently, is an apomorphic character for the Hymenomycetidae. Mycorrhizal taxa of Sebacinaceae, including mycobionts of ectomycorrhizas, orchid mycorrhizas, ericoid mycorrhizas, and jungermannioid mycorrhizas, are distributed over two subgroups. One group contains species with macroscopically visible basidiomes, whereas members of the other group probably lack basidiomes. Sebacina appears to be polyphyletic; current species concepts in Sebacinaceae are questionable. Sebacina vermifera sensu Warcup & Talbot consists of a broad complex of species possibly including mycobionts of jungermannioid and ericoid mycorrhizas. This wide spectrum of mycorrhizal types in one fungal family is unique. Extrapolating from the known rDNA sequences in Sebacinaceae, it is evident that there is a cosm of mycorrhizal biodiversity yet to be discovered in this group. Taxonomically, we recognise the Sebacinaceae as constituting a new order, the Sebacinales.

Phylogenetic relationships in Cortinarius , section Calochroi , inferred from nuclear DNA sequences

BackgroundSection Calochroi is one of the most species-rich lineages in the genus Cortinarius (Agaricales, Basidiomycota) and is widely distributed across boreo-nemoral areas, with some extensions into meridional zones. Previous phylogenetic studies of Calochroi (incl. section Fulvi) have been geographically restricted; therefore, phylogenetic and biogeographic relationships within this lineage at a global scale have been largely unknown. In this study, we obtained DNA sequences from a nearly complete taxon sampling of known species from Europe, Central America and North America. We inferred intra- and interspecific phylogenetic relationships as well as major morphological evolutionary trends within section Calochroi based on 576 ITS sequences, 230 ITS + 5.8S + D1/D2 sequences, and a combined dataset of ITS + 5.8S + D1/D2 and RPB1 sequences of a representative subsampling of 58 species.ResultsMore than 100 species were identified by integrating DNA sequences with morphological, macrochemical and ecological data. Cortinarius section Calochroi was consistently resolved with high branch support into at least seven major lineages: Calochroi, Caroviolacei, Dibaphi, Elegantiores, Napi, Pseudoglaucopodes and Splendentes; whereas Rufoolivacei and Sulfurini appeared polyphyletic. A close relationship between Dibaphi, Elegantiores, Napi and Splendentes was consistently supported. Combinations of specific morphological, pigmentation and molecular characters appear useful in circumscribing clades.ConclusionOur analyses demonstrate that Calochroi is an exclusively northern hemispheric lineage, where species follow their host trees throughout their natural ranges within and across continents. Results of this study contribute substantially to defining European species in this group and will help to either identify or to name new species occurring across the northern hemisphere. Major groupings are in partial agreement with earlier morphology-based and molecular phylogenetic hypotheses, but some relationships were unexpected, based on external morphology. In such cases, their true affinities appear to have been obscured by the repeated appearance of similar features among distantly related species. Therefore, further taxonomic studies are needed to evaluate the consistency of species concepts and interpretations of morphological features in a more global context. Reconstruction of ancestral states yielded two major evolutionary trends within section Calochroi: (1) the development of bright pigments evolved independently multiple times, and (2) the evolution of abruptly marginate to flattened stipe bulbs represents an autapomorphy of the Calochroi clade.

Phylogenetic relationships of the downy mildews (Peronosporales) and related groups based on nuclear large subunit ribosomal DNA sequences

In order to investigate phylogenetic relationships of the Peronosporomycetes (Oomycetes), nuclear large subunit ribosomal DNA sequences containing the D1 and D2 region were analyzed of 92 species belonging to the orders Peronosporales, Pythiales, Leptomitales, Rhipidiales, Saprolegniales and Sclerosporales. The data were analyzed applying methods of neighbor-joining as well as maximum parsimony, both statistically supported using the bootstrap method. The results confirm the major division between the Pythiales and Peronosporales on the one hand and the Saprolegniales, Leptomitales, and Rhipidiales on the other. The Sclerosporales were shown to be polyphyletic; while Sclerosporaceae are nested within the Peronosporaceae, the Verrucalvaceae are merged within the Saprolegniales. Within the Peronosporomycetidae, Pythiales as well as Peronosporales as currently defined are polyphyletic. The well supported Albugo clade appears to be the most basal lineage, followed by a Pythium-Lagenidium clade. The third, highly supported clade comprises the Peronosporaceae together with Sclerospora, Phytophthora, and Peronophythora. Peronophythora is placed within Phytophthora, indicating that both genera should be merged. Bremiella seems to be polyphyletic within the genus Plasmopara, suggesting a transfer to Plasmopara. The species of Peronospora do not appear as a monophyletic group. Peronospora species growing on Brassicaceae form a highly supported clade.

Sebacinales Everywhere: Previously Overlooked Ubiquitous Fungal Endophytes

Inconspicuous basidiomycetes from the order Sebacinales are known to be involved in a puzzling variety of mutualistic plant-fungal symbioses (mycorrhizae), which presumably involve transport of mineral nutrients. Recently a few members of this fungal order not fitting this definition and commonly referred to as ‘endophytes’ have raised considerable interest by their ability to enhance plant growth and to increase resistance of their host plants against abiotic stress factors and fungal pathogens. Using DNA-based detection and electron microscopy, we show that Sebacinales are not only extremely versatile in their mycorrhizal associations, but are also almost universally present as symptomless endophytes. They occurred in field specimens of bryophytes, pteridophytes and all families of herbaceous angiosperms we investigated, including liverworts, wheat, maize, and the non-mycorrhizal model plant Arabidopsis thaliana. They were present in all habitats we studied on four continents. We even detected these fungi in herbarium specimens originating from pioneering field trips to North Africa in the 1830s/40s. No geographical or host patterns were detected. Our data suggest that the multitude of mycorrhizal interactions in Sebacinales may have arisen from an ancestral endophytic habit by specialization. Considering their proven beneficial influence on plant growth and their ubiquity, endophytic Sebacinales may be a previously unrecognized universal hidden force in plant ecosystems.

Phylogenetic relationships in Auriculariales and related groups—hypotheses derived from nuclear ribosomal DNA sequences

In order to estimate phylogenetic relationships in the Auriculariales sensu Bandoni (1984) and allied groups we have analysed a representative sample of species by comparison of nuclear coded ribosomal DNA sequences, applying models of neighbour joining, maximum parsimony, conditional clustering, and maximum likelihood. Analyses of the 5’ terminal domain of the gene coding for the 28 S ribosomal large subunit supported the monophyly of the Dacrymycetales and Tremellales, while the monophyly of the Auriculariales was not supported. The Sebacinaceae, including the genera Sebacina, Efibulobasidium, Tremelloscypha, and Craterocolla, was confirmed as a monophyletic group, which appeared distant from other taxa ascribed to the Auriculariales. Within the latter the following subgroups were significantly supported: (1) a group of closely related species containing members of the genera Auricularia, Exidia, Exidiopsis, Heterochaete, and Eichleriella; (2) a group comprising species of Bourdotia and Ductifera; (3) a group of globose-spored species of the genus Basidiodendron; (4) a group that includes the members of the genus Myxarium and Hyaloria pilacre; (5) a group consisting of species of the genera Protomerulius, Tremellodendropsis, Heterochaetella, and Protodontia. Additional analyses of the internal transcribed spacer (ITS) region of the species contained in group (1) resulted in a separation of these fungi due to their basidial types.

The simple-septate basidiomycetes: a synopsis

The simple-septate basidiomycetes comprise more than 8,000 species that show a high morphological and ecological heterogeneity. To gain insight in the phylogenetic relationships within this group, we compared several ultrastructural features such as septal pore apparatus, form, and behavior of the spindle pole bodies, types of host–parasite interaction, presence or absence of colacosomes, symplechosomes, atractosomes, and cystosomes as well as nuclear rDNA sequences coding for small- and large-subunit rRNA. Based on our integrated analysis, we propose a new classification system for the simple-septate basidiomycetes with the subphylum Pucciniomycotina and the classes Agaricostilbomycetes, Atractiellomycetes, Classiculomycetes, Cryptomycocolacomycetes, Cystobasidiomycetes, Microbotryomycetes, Mixiomycetes, and Pucciniomycetes. We also propose the pucciniomycotinous taxa Cystobasidiales, Erythrobasidiales, Helicobasidiales, Mixiales, Naohideales, Pachnocybales, Spiculogloeales, and Kondoaceae and the new subphyla Agaricomycotina (equivalent to the current Hymenomycetes) and Ustilaginomycotina (equivalent to the current Ustilaginomycetes).

An in vitro method for establishing mycorrhizae on coniferous tree seedlings

SummaryA method for in vitro synthesis of mycorrhizae on coniferous tree seedlings is described. Tree seedlings (Larix decidua Mill., Picea abies (L.) Karst, and Pinus sylvestris L.) and fungi Amanita muscaria (L. ex Fr.) Hooker, Piloderma croceum Erikss. et Hjorst., Pisolithus tinctorius (Pers.) Coker et Couch, and Suillus grevillei (Klotzsch) Singer were maintained under sterile conditions in petri dishes. Typical ectomycorrhizae were established within 2–3 weeks after inoculation and within 2 months after germination of seedlings. Eventually a high percentage of mycorrhizal root tips was obtained.

Mycorrhiza of forest trees — structure and function

Comprehensive surveys on mycorrhizae have recently been published by Harley and Smith (1983) and Strullu (1985). Harley (1984) has also briefly summarized mycorrhizal associations in general, whilst Moser and Haselwandter (1983) reported on the ecophysiology and Duddridge (1985) on the interface in mycorrhizae of Agaricales. France and Reid (1983) presented a compilation of the current knowledge regarding the nitrogen and carbon physiology of ectomycorrhizae. The main interest of the present paper lies in the interpretation of the morphology and ultrastructure of ectomycorrhizae of forest trees in respect of their function in the uptake and exchange of nutrients. The protectional ability of mycorrhizae is also considered briefly. Recent studies have shown the surprising similarity in the structure of the Hartig net and significant differences in the structure of the mantles of different mycorrhiza-forming fungal species, thus confirming the early report by Mangin (1910). This review article therefore deals firstly with more general aspects, that is the structure and function of the Hartig net in respect to nutrient exchange and transport, and secondly with the more specialized structures of the hyphal mantle, including hyphal strands and rhizomorphs and their function in nutrient uptake and storage. Finally, developmental changes of structure and function and those caused by environmental conditions are discussed.

Mycorrhizal status of indigenous trees in dry Afromontane forests of Ethiopia

Abstract The dry Afromontane forests in Ethiopia are composed of a number of indigenous tree species. Currently, indigenous trees are declining at an alarming rate in this ecosystem. The few reforestation programs, which have so far been undertaken, employ exotic tree species. This is mainly due to lack of knowledge on the environmental requirements of indigenous trees. Though there have been efforts to solve problems associated with the use of indigenous trees in the reforestation activities, information on the mycorrhizal symbiosis is still lacking. Investigation of roots of 11 indigenous trees, Albizia gummifera , Albizia schimperiana , Aningeria adolfi - friedericii , Croton machrostachyus , Ekebergia capensis , Hagenia abyssinica , Juniperus procera , Podocarpus falcatus , Prunus africana , Olea europaea ssp. cuspidata , and Syzygium guineense , revealed arbuscular mycorrhizal colonization. No evidence of ectomycorrhizal colonization was found. This is the first report on the mycorrhizal status of A. gummifera , A. schimperiana , A. adolfi - friedericii , E. capensis , H. abyssinica , P. africana and S. guineense. The mycorrhizas are characterized by dominantly intercellular hyphal growth, formation of arbuscules on intracellular hyphal branches and low frequency of hyphal coils which can be classified as an Arum -type of AM. The Arum -type of AM is reported for the first time in S. guineense (Myrtaceae), E. capensis (Meliaceae), A. adolfi - friedericii (Sapotaceae) and the gymnosperms J. procera and P. falcatus . Results established that arbuscular mycorrhizas (AM) are predominant in the dry Afromontane forests of Ethiopia. Therefore, AM should receive special attention in indigenous tree seedling production and restoration activities of the dry Afromontane ecosystems of the country.

Phylogeny of Hyaloperonospora based on nuclear ribosomal internal transcribed spacer sequences

Phylogenetic relationships in Hyaloperonospora (Oomycetes) were investigated by molecular analyses using internal transcribed spacer (ITS) sequences and collections from different host plants. Trees were inferred with Bayesian Markov chain Monte Carlo, neighbor-joining and maximum parsimony methods and rooted with Perofascia. The results are discussed with respect to host taxonomy and species concepts of downy mildews from the literature. Molecular data mainly support the use of narrow species delimitations and host range as a taxonomic marker. Hyaloperonospora brassicae turns out to be a non-monophyletic assemblage of different species. New combinations are proposed in accordance with the phylogenetic trees.