Miscellaneous Contribution to the Anatomy and Molecular phylogeny of tropical African resupinate Thelephorales (Basidiomycota, Fungi)

Episode von Fakultät für Biologie - Digitale Hochschulschriften der LMU - Teil 03/06 von Ludwig-Maximilians-Universität München · 26. Februar 2008

The Thelephorales (Basidiomycota, Fungi) form a monophyletic group with approximately 177 accepted species. The Thelephorales are cosmopolitan and encompass mainly ectomycorrhizal species. Unlike many fungal lineages, evolutionary trends within and between members of Thelephorales still remain incompletely assessed. Additionally, most phylogenetic investigations on fungi have failed to include representative samples from tropical Africa. In the present study started four years ago, we have assessed and documented some of the diversity of tropical African Thelephorales. It represents a part of a future broader but continuous project aiming for a complete monograph, and highlighting the anatomical and molecular relevance of tropical species in the evolutionary interpretation of Thelephorales in general. The study was started in the northern Guinean seasonal forests, located from central to north Benin (West Africa). Northern Guinean seasonal forests are characterised by a low specific plant richness, but predominated by a few ectomycorrhizal trees of the Caesalpiniaceae (Isoberlinia doka Craib & Stapf Isoberlinia tomenteosa (Harms) Craib & Stapf, Burkea africana Hook., and Afzelia africana Smith), Dipterocarpaceae (Monothes kerstingii Gilg.) and Euphorbiaceae (Uapaca guineensis Müll. Arg.). Four collecting trips were undertaken during the rainy seasons of 2003, 2004, 2005 and 2006. Specimens of Thelephorales and soil cores were randomly sampled under native ectomycorrhizal trees. The collecting trips yielded over 800 specimens of Thelephorales and 60 EcM samples in total. Taxonomic investigations and species concepts of the specimens were assessed using a combination of both molecular and anatomo-morphological approaches.

All examined specimens were sorted into 19 morphologically different species. In this dissertation four new species are described and illustrated. A full description is provided for each species, together with reliable line drawings and, where possible, with SEM micrographs. Anatomic studies have confirmed and emphasised the commonality of irregularly shaped thin hyphae on the rhizomorph surfaces of many African species. Novel anatomical features hitherto unknown within Thelephorales, and rarely recorded for Hymenomycetes in general, are recorded. Detailed anatomical comparison with type species has enabled us to depict fundamental arguments about the discrimination of thelephoroid genera. We report fundamental differences in spore ornamentation between African and temperate tomentelloid species.

Using molecular PCR methods, we confirmed the high divergence rate of the ITS regions of thelephoroid fungi. Within morphologically close specimens, the ITS rDNA sequence deviation generally ranges between 0.0 to 2.68%. However, genetic distance between some specimens (e.g.Tomentella furcata Yorou & Agerer and T. cf. furcata nom. prov.) illustrates how morphologically convergent specimens may be greatly divergent with regard to their ITS rDNA. Phylogenetically, tropical African species of Thelephorales are either basal or terminal within various clades of investigated temperate, boreal and tropical species. Generally, they highly deviate from temperate and boreal closest species by 4.3 to 12.9% with regard to the ITS rDNA sequences.

Northern Guinean seasonal forests harbour a great diversity of Thelephorales that are, however, hard to detect due to the down-facing growth of fruit bodies of most resupinate Thelephorales, and the annual burning of required substrates. Only one species, Tomentella africana Yorou & Agerer, is widespread and commonly recorded. Many other species occur scarcely on fragmented substrates. Though the Thelephorales are cosmopolitan, we failed to record species that are reported to have a worldwide distribution. Notably, representatives of the resupinate thelephoroid genera Pseudotomentella Svrček and Tomentellopsis Hjortstam were missing, as well as species of the mainly temperately distributed family Bankeraceae. In this study, we provide evidence of the ectomycorrhizal formation between Thelephorales and native tropical African forest trees. Anatomical and molecular characterisation of ectomycorrhizae formed between Thelephorales and native West African forest trees (namely Afzelia africana and Uapaca guineensis) are provided for the first time.

The present studies are based on original material collected in some Ceasalpinioid /Euphorbiaceae-dominated vegetation types found from central to north Benin. The Zambesian Centre of Endemism, located in South-East Africa, also harbours a variety of different ectomycorrhizal trees including Brachstegia spp, Julbernadia spp, and Isoberlinia spp. Stands dominated by monospecific ectomycorrhizal forest trees are also present in the rain forests of South Cameroon. The variety of ectomycorrhizal tree species present in tropical Africa implies a greater species richness of Thelephorales than that currently reported from Benin.

The present thesis represents a keystone study and provides baseline data for a continuing monograph of Thelephorales in tropical Africa. Intensive monographic and taxonomical investigations will undoubtedly reveal many interesting, and probably plesiomorphic, anatomical features from tropical Thelephorales. In this context, detailed anatomical investigations integrated with DNA sequence analyses and phylogenetic inferences are promising tools for discriminating thelephoroid species in general, and tropical ones in particular.

Taxonomic novelties in this study:

Tomentella capitata Yorou & Agerer

Tomentella brunneocystidia Yorou & Agerer

Tomentella furcata Yorou & Agerer

Tomentella africana Yorou & Agerer

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