The dark side is not fastidious--dark septate endophytic fungi of native and invasive plants of semiarid sandy areas

Dark septate endophytic (DSE) fungi represent a frequent root-colonizing fungal group common in environments with strong abiotic stress, such as (semi)arid ecosystems. This work aimed to study the DSE fungi colonizing the plants of semiarid sandy grasslands with wood steppe patches on the Great Hungarian Plain. As we may assume that fungi colonizing both invasive and native species are generalists, root associated fungi (RAF) were isolated from eight native and three invasive plant species. The nrDNA sequences of the isolates were used for identification. To confirm that the fungi were endophytes an artificial inoculation system was used to test the isolates: we considered a fungus as DSE if it colonized the roots without causing a negative effect on the plant and formed microsclerotia in the roots. According to the analyses of the ITS sequence of nrDNA the 296 isolates clustered into 41 groups. We found that 14 of these 41 groups were DSE, representing approximately 60% of the isolates. The main DSE groups were generalist and showed no specificity to area or season and colonized both native and invasive species, demonstrating that exotic plants are capable of using the root endophytic fungi of the invaded areas. The DSE community of the region shows high similarity to those found in arid grasslands of North America. Taking into account a previous hypothesis about the common root colonizers of those grasslands and our results reported here, we hypothesize that plants of (semi)arid grasslands share common dominant members of the DSE fungal community on a global scale.

Colonization of roots of cultivated Solanum lycopersicum by dark septate and other ascomycetous endophytes

Tomato (Solanum lycopersicum L.) roots from four different crop sites in Colombia were surface sterilized and 51 fungal isolates were obtained and conserved for further analysis. Based on microscopical observations and growth characteristics, 20 fungal isolates corresponded to genus Fusarium, six presented asexual conidia different from Fusarium, eight were sterile mycelia, seven of which had dark septate hyphae and 17 did not continue to grow on plates after being recovered from conservation. Growth on different media, detailed morphological characterization and ITS region sequencing of the six sporulating and eight sterile isolates revealed that they belonged to different orders of Ascomycota and that the sterile dark septate endophytes did not correspond to the well known Phialocephala group. Interactions of nine isolates with tomato plantlets were assessed in vitro. No effect on shoot development was revealed, but three isolates caused brown spots in roots. Colonization patterns as analyzed by confocal microscopy differed among the isolates and ranged from epidermal to cortical penetration. Altogether 11 new isolates from root endophytic fungi were obtained, seven of which showed features of dark septate endophytes. Four known morphotypes were represented by five isolates, while six isolates belonged to five morphotypes of putative new unknown species.

Diversity of sterile root-associated fungi of two Mediterranean plants

•  The diversity of dark sterile mycelia (DSM) associated with the roots of neighboring healthy ectomycorrhizal Pinus halepensis and endomycorrhizal Rosmarinus officinalis plants in a Mediterranean ecosystem in Italy was investigated to assess taxonomic affinities of these poorly known root endophytes. •  More than 260 fungal isolates were obtained and ascribed to distinct morphotypes based on their macro- and microscopic features. Polymerase chain reaction-restriction fragment length polymorphism and sequence analyses of the internal transcribed spacers (ITS1-5.8S-ITS2) and 18S rDNA regions were carried out for representatives of the morphotypes obtained from both hosts over an 11-yr period. •  Molecular evidence matched morphological group circumscription. Recognition of systematic affinities was possible with varying degrees of resolution for the different morphotypes. Morph 2 was closely related to Rhizopycnis vagum (within Dothideomycetidae), Morph 1 to Diaporthe / Phomopsis (within Sordariomycetidae), whereas Morphs 3a, 3b, 3c and 3d could only be given taxonomic placement at a higher level (Dothideomycetidae and Chaetothyriomycetidae). •  This peculiar systematic spectrum suggests that actual DSM diversity in nature is still largely underestimated. Morphophysiological convergence among morphotypes, and ecological traits possibly involved in interactions with plant hosts are discussed.