No abstract

Ash dieback caused by the mitosporic ascomycete Chalara fraxinea is a novel disease of major concern affecting Fraxinus excelsior and Fraxinus angustifolia in large parts of Europe. Recently, its teleomorph was detected and assigned to Hymenoscyphus albidus, which has been known from Europe since 1851. In this study, we present molecular evidence for the existence of two morphologically very similar taxa, H. albidus, which is lectotypified and Hymenoscyphus pseudoalbidus sp. nov. Differences were found between the species in the loci calmodulin, translation elongation factor 1-a and the internal transcribed spacers of the rDNA genes, and strong differentiation was obtained with ISSR markers. It is likely that H. albidus is a non-pathogenic species, whereas H. pseudoalbidus is a virulent species causing ash dieback. Genotyping herbarium specimens showed that H. pseudoalbidus has been present in Switzerland for at least 30 years prior to the outbreak of the epidemic.

Endophytic fungi are a taxonomically and ecologically heterogenous group of organisms, mainly belonging to the Ascomycotina and Deuteromycotina. The isolation methods affect the species composition of the endophyte assemblage in a given host. The number of endophyte taxa isolated from a host species is usually large; however, only few, normally host specific species or strains are dominant. Endophyte assemblages are specific at the host species level, but species composition and frequencies are significantly affected by site-specific conditions. Moreover, the relative importance and number of endophytic species vary among individuals within sites. In some cases, each individual could be considered a separate ecosystem. In general, however, 40 individuals with 30 to 40 sampling units per organ and individual should be enough to detect 80% of taxa present in a given host at one site. Endophytes usually produce the enzymes necessary for the colonization of plant tissues. Substrate utilization studies and isozyme analysis have demonstrated that most endophytes are able to utilize most plant cell components. The production of growth promoting factors and of metabolites useful in the pharmaceutical and agricultural industry is widespread among endophytic fungi. The usefulness of endophytes in agricultural and pharmaceutical research is briefly discussed.

Once the disease is established, management is hardly possible. The occurrence of a small fraction of partially tolerant trees constitutes hope for resistance breeding in the future. Healthy-looking trees should be preserved.

Dark septate endophytes (DSE), a diverse group of ascomycetes, are dominant root colonizers in many ecosystems. The most frequent DSE in natural forest ecosystems in the Northern hemisphere belong to the Phialocephala fortinii s.l. – Acephala applanata species complex (PAC). Recently, species rank was assigned to seven cryptic species (CSP) of P. fortinii s.l.: Phialocephala fortinii s. str. C.J.K. Wang & H.E. Wilcox, Phialocephala europaea C.R. Grünig et T.N. Sieber, Phialocephala helvetica C.R. Grünig et T.N. Sieber, Phialocephala letzii C.R. Grünig et T.N. Sieber, Phialocephala subalpina C.R. Grünig et T.N. Sieber, Phialocephala turiciensis C.R. Grünig et T.N. Sieber, and Phialocephala uotolensis C.R. Grünig et T.N. Sieber. PAC species occur on all parts of the root system of trees, from mycorrhizal root tips to the stem base. Up to 80% of fine roots in forest stands can be colonized by them, and up to eight species occur sympatrically. The present work is a mixture of review and reconsideration of published work in the light of the subdivision of P. fortinii s.l. into several species. We review the current knowledge related to taxonomy, geographical distribution, population biology, and ecology of PAC species. We identified strains of P. fortinii s.l. from previously published studies to species level. The reassessment of earlier studies indicates that PAC species behave in a versatile manner along the mutualism-parasitism continuum and lifestyle designation is complicated by the use of different experimental systems. Finally we define the most promising research areas, which will contribute to elucidate the ecological role of root endophytes in general and PAC species in particular.