Endophytic mycobiota of leaves and roots of the grass Holcus lanatus

A pilot study of antioxidant potential of endophytic fungi from some Sudanese medicinal plants

OBJECTIVE

To evaluate the total phenolic content and total antioxidant capacity of ethyl acetate extracts of 21 endophytic fungi isolated from five Sudanese medicinal plants: Calotropis procera, Catharanthus roseus, Euphorbia prostrate, Vernonia amygdalina and Trigonella foenum-graecum.

METHODS

Crude extracts of endophytic fungi and their host plants were tested by classical Folin-Ciocalteu colorimetric method to determine the total phenolic content, also total antioxidant capacity was estimated using 1,1-diphenyl-2-picrylhydrazyl free radical scavenging in vitro method.

RESULTS

Among the endophytes, endophytic fungus Aspergillus sp. from Trigonella foenum-graecum seeds demonstrated the highest both total phenolic content in term of gallic acid equivalent [(89.9 ± 7.1) mg GAE/g] and antioxidant activity for 1,1-diphenyl-2-picrylhydrazyl radical scavenging assay [IC50: (18.0 ± 0.1) μg/mL]. A high positive linear correlation (R(2) = 0.999 1) was found between total antioxidant capacity and total phenolic content of endophytic fungi isolated from Vernonia amygdalina.

CONCLUSIONS

The present study revealed that some endophytic fungi from the five Sudanese medicinal plants could be a potential source of novel natural antioxidant compounds.

Phylogenic diversity and tissue specificity of fungal endophytes associated with the pharmaceutical plant, Stellera chamaejasme L. revealed by a cultivation-independent approach

The fungal endophytes associated with medicinal plants have been demonstrated as a reservoir with novel natural products useful in medicine and agriculture. It is desirable to explore the species composition, diversity and tissue specificity of endophytic fungi that inhabit in different tissues of medicinal plants. In this study, a culture-independent survey of fungal diversity in the rhizosphere, leaves, stems and roots of a toxic medicinal plant, Stellera chamaejasme L., was conducted by sequence analysis of clone libraries of the partial internal transcribed spacer region. Altogether, 145 fungal OTUs (operational taxonomic units), represented by 464 sequences, were found in four samples, of these 109 OTUs (75.2 %) belonging to Ascomycota, 20 (13.8 %) to Basidiomycota, 14 (9.7 %) to Zygomycota, 1 (0.7 %) to Chytridiomycota, and 1 (0.7 %) to Glomeromycota. The richness and diversity of fungal communities were strongly influenced by plant tissue environments, and the roots are associated with a surprisingly rich endophyte community. The endophyte assemblages associated with S. chamaejasme were strongly shaped by plant tissue environments, and exhibited a certain degree of tissue specificity. Our results suggested that a wide variety of fungal assemblages inhabit in S. chamaejasme, and plant tissue environments conspicuously influence endophyte community structure.

Fungal endophytic communities on twigs of fast and slow growing Scots pine (Pinus sylvestris L.) in northern Spain

Most plant species harbour a diverse community of endophytic, but their role is still unknown in most cases, including ecologically and economically important tree species. This study describes the culturable fungal endophytic community of Pinus sylvestris L. twigs in northern Spain and its relationship with diametric growth of the host. In all, 360 twig samples were collected from 30 Scots pines in fifteen stands. Isolates were obtained from all twig samples and 43 fungal taxa were identified by morphogrouping and subsequent ITS rDNA sequencing. All isolates were Ascomycetes, being Dothideomycetes and Sordariomycetes the most abundant classes. Half of the species were host generalists while the others were conifer or pine specialists. We found three new endophytic species for the Pinaceae: Biscogniauxia mediterranea, Phaeomoniella effusa and Plectania milleri, and additional six new species for P. sylvestris: Daldinia fissa, Hypocrea viridescens, Nigrospora oryzae, Ophiostoma nigrocarpum, Penicillium melinii and Penicillium polonicum. The endophytic community of fast and slow growing trees showed differences in species composition, abundance and evenness, but not in diversity. Phoma herbarum was associated to fast growing trees and Hypocrea lixii to those growing slow. Our results support the hypothesis that some endophytic species may affect growth of P. sylvestris.

Bioactive bile salt-capped silver nanoparticles activity against destructive plant pathogenic fungi through in vitro system

Sodium deoxycholate (NaDC) capped silver nanoparticles are employed to counteract the fungusColletotrichum gloeosporioideswhich causes anthracnose disease in a wide number of plants throughout the world.

Is the prominent ericoid mycorrhizal fungus Rhizoscyphus ericae absent in the Southern Hemisphere's Ericaceae? A case study on the diversity of root mycobionts in Gaultheria spp. from northwest Patagonia, Argentina

Ericaceae diversity hotspots are in the mountains of the Neotropics and Papua New Guinea, South Africa's fynbos and Southeast Asia but majority of references to their root mycobionts come from the Northern Hemisphere. Here, typical cultivable ericoid mycorrhizal (ErM) fungi comprise Rhizoscyphus ericae, Meliniomyces variabilis, and Oidiodendron maius. It is however unclear whether this is true also for the Southern Hemisphere. Our study focused on cultivable mycobionts from hair roots of Gaultheria mucronata and Gaultheria poeppigii (Ericaceae) from two natural forests in NW Patagonia, Argentina, differing in mycorrhizal preferences of their tree dominants. We detected 62 well-defined OTUs mostly belonging to Helotiales and Hypocreales; the most frequent were Phialocephala fortinii s. l., Pochonia suchlasporia, and Ilyonectria radicicola. Only one out of 257 isolates showed ITS nrDNA similarity to members of the R. ericae aggregate (REA) but was not conspecific with R. ericae, and only five isolates were conspecific with O. maius. Microscopic observations showed that the screened roots were frequently colonized in a manner differing from the pattern typically produced by R. ericae and O. maius. A re-synthesis experiment with selected isolates showed that only O. maius formed colonization resembling ericoid mycorrhiza. Amplification of root fungal DNA with REA-specific and Sebacinaceae-specific primers showed that REA mycobionts were present in some of the screened samples while Sebacinaceae were present in all samples. These results suggest that Gaultheria spp. from NW Patagonia form ericoid mycorrhizae predominantly with the difficult-to-cultivate Sebacinaceae while the incidence of REA is relatively low and may be masked by other most likely non-mycorrhizal cultivable mycobionts.

Temperate pine barrens and tropical rain forests are both rich in undescribed fungi

Most of fungal biodiversity on Earth remains unknown especially in the unexplored habitats. In this study, we compared fungi associated with grass (Poaceae) roots from two ecosystems: the temperate pine barrens in New Jersey, USA and tropical rain forests in Yunnan, China, using the same sampling, isolation and species identification methods. A total of 426 fungal isolates were obtained from 1600 root segments from 80 grass samples. Based on the internal transcribed spacer (ITS) sequences and morphological characteristics, a total of 85 fungal species (OTUs) belonging in 45 genera, 23 families, 16 orders, and 6 classes were identified, among which the pine barrens had 38 and Yunnan had 56 species, with only 9 species in common. The finding that grass roots in the tropical forests harbor higher fungal species diversity supports that tropical forests are fungal biodiversity hotspots. Sordariomycetes was dominant in both places but more Leotiomycetes were found in the pine barrens than Yunnan, which may play a role in the acidic and oligotrophic pine barrens ecosystem. Equal number of undescribed fungal species were discovered from the two sampled ecosystems, although the tropical Yunnan had more known fungal species. Pine barrens is a unique, unexplored ecosystem. Our finding suggests that sampling plants in such unexplored habitats will uncover novel fungi and that grass roots in pine barrens are one of the major reservoirs of novel fungi with about 47% being undescribed species.

Tall fescue is a potential spillover reservoir host for Alternaria species

The spread of invasive species is complicated and multifaceted. Enemy spillover (i.e. the transfer of a natural enemy from a reservoir host to a novel host) is one mechanism that facilitates the spread of non-native species. The reservoir host is a species that harbors high abundance of the enemy with little cost to fitness. We asked whether Schedonorus arundinaceus (tall fescue), a highly invasive grass species in North America, is a potential reservoir host for the ubiquitous genus of fungi, Alternaria. We also asked whether spillover of Alternaria is possible among grasses that commonly occur with S. arundinaceus in grassland ecosystems. We performed a greenhouse cross inoculation of three isolates of Alternaria and six grass species (three native, three invasive, including S. arundinaceus). We determined that spillover is possible because the fungal isolates infected and caused disease symptoms on all six grasses and decreased biomass in two of the grass species. We also determined that the invasive grass species appear to be more competent hosts than the native species and that S. arundinaceus could be a likely reservoir host for Alternaria spp. because it can harbor the pathogen with no apparent fitness cost.

Endophytic fungi associated with Macrosolen tricolor and its host Camellia oleifera

Endophytic fungi play an important role in terrestrial ecosystem, while little is known about those in hemi-parasitic plants, a group of special plants which absorb nutrients from its hosts by haustoria. The relationship of the endophytes in the two parts of the bipartite systems (hemiparasites together with their hosts) is also poorly understood. Endophytic fungi of a hemi-parasitic plant Macrosolen tricolor, and its host plant Camellia oleifera were investigated and compared in this study. M. tricolor contained rich and diversified endophytic fungi (H' = 2.829), which consisted mainly of ascomycetes, distributed in more than ten orders of four classes (Sordariomycetes, Dothideomycetes, Leotiomycetes and Eurotiomycetes) besides Incertae sedis strains (23.2 % of total). In addition, 2.2 % of isolates were identified to be Basidiomycota, all of which belonged to Agaricomycetes. Obvious differences were observed between the endophytic fungal assembles in the leaves and those in the branches of M. tricolor. The endophytic fungi isolated from C. oleifera distributed in nearly same orders of the four classes of Ascomycota and one class (Agaricomycetes) of Basidiomycota as those from M. tricolor with similar proportion. For both M. tricolor and C. oleifera, Valsa sp. was the dominant endophyte species in the leaves, Torula sp. 1 and Fusarium sp. 1 were the dominant endophytic fungi in the branches. The similarity coefficient of the endophyte assembles in the two host was 64.4 %. Canonical correspondence analysis showed that the endophyte assembles of M. tricolor and C. oleifera were significantly different (p < 0.01).

Diversity and dynamics of fungal endophytes in leaves, stems and roots of Stellera chamaejasme L. in northwestern China

This study was conducted to explore fungal endophyte communities inhabiting a toxic weed (Stellera chamaejasme L.) from meadows of northwestern China. The effects of plant tissue and growth stage on endophyte assemblages were characterized. Endophytes were recovered from 50 % of the samples, with a total of 714 isolates. 41 operational taxonomical units (OTUs) were identified, consisting of 40 OTUs belonging primarily to Ascomycota and 1 OTU belonging to Basidiomycota. Pleosporales and Hypocreales were the orders contributing the most species to the endophytic assemblages. The total colonization frequency and species richness of endophytic fungi were higher in roots than in leaves and stems. In addition, for the plant tissues, the structure of fungal communities differed significantly by growth stages of leaf emergence and dormancy; for the plant growth stages, the structure of fungal communities differed significantly by plant tissues. This study demonstrates that S. chamaejasme serves as a reservoir for a wide variety of fungal endophytes that can be isolated from various plant tissues.

Multiplexed interactions: viruses of endophytic fungi

Mycoviruses have been detected from all four classes of fungal endophytes. The virus species richness is probably extremely high in endophytes. The incidence and diversity of mycoviruses may be affected by transmission modes, virus-fungus-plant interactions, and endophyte population structures. Endophyte viruses are unlikely to be strong antagonists to their fungal hosts and can clearly play mutualistic roles in the multiplex symbioses with endophytes and plants under some environmental conditions. A better understanding of fungal endophyte viruses will help prospects of future applications for sustainable agriculture.

Production of phenolics and the emission of volatile organic compounds by perennial ryegrass (Lolium perenne L.)/Neotyphodium lolii association as a response to infection by Fusarium poae

Grasses very often form symbiotic associations with Neotyphodium/Epichloë endophytic fungi. These endophytes often allow the host grass to be protected from different pathogens. However, there is little known about the mechanisms of such endophyte influence on the host. Thus, the purpose of this research was to examine the effect of the N. lolii endophyte on the total production of phenolic compounds, VOCs emission and the resistance of three perennial ryegrass genotypes infected by pathogenic Fusarium poae. Analyses of total phenolics content were performed in control (not inoculated) and inoculated plants after 1, 2, 3, 4, 5, and 6 days (DAI) and for VOCs after 0, 3, 6 and 12 DAI. The presence of endophytes significantly reduced the disease index in two of the three genotypes relative to that in E-. Plants infected by N. lolii exhibited higher production of phenolics relative to the E- plants. The highest amounts of phenolics were observed on the second and sixth DAI. Genotype Nl22 showed the strongest effect of the endophyte on the production of phenolics, which increased by over 61%. Both the endophyte infected and non-infected plants emitted most abundantly two GLVs ((Z)-3-hexenal, (Z)-3-hexen-1-yl acetate), three terpenes (linalool, (Z)-ocimene, β-caryophyllene) and three shikimic acid pathway derivatives (benzyl acetate, indole, and methyl salicylate). The endophyte presence and the intervals of VOCs detection were a highly significant source of variation for all emitted volatiles (P<0.001). The genotype of the perennial ryegrass significantly affected only the emission of methyl salicylate (P<0.05) and β-caryophyllene (P<0.05). Most of the VOCs ((Z)-3-hexen-1-yl acetate, (Z)-3-hexenal, linalool and methyl salicylate) reached their highest levels of emission on the sixth DAI, when averaged over genotypes and endophyte status. The results highlight the role of Neotyphodium spp. in the mediation of quadro-trophic interactions among plants, symbiotic endophytes, invertebrate herbivores and plant pathogenic fungi. Our results also confirm the fact that symbiotic plants can activate a defense reaction faster than non-symbiotic plants after a pathogen attack. Thus, N. lolii can be involved in the defense of perennial ryegrass against pathogens and potentially could be central to the host plants' protection.

Hidden host plant associations of soilborne fungal pathogens: an ecological perspective

Much of the current knowledge on population biology and ecology of soilborne fungal pathogens has been derived from research based on populations recovered from plants displaying disease symptoms or soil associated with symptomatic plants. Many soilborne fungal pathogens are known to cause disease on a large number of crop plants, including a variety of important agronomical, horticultural, ornamental, and forest plants species. For instance, the fungus Verticillium dahliae causes disease on >400 host plants. From a phytopathological perspective, plants on which disease symptoms have not been yet observed are considered to be nonhosts for V. dahliae. This term may be misleading because it does not provide information regarding the nature of the plant-fungus association; that is, a nonhost plant may harbor the fungus as an endophyte. Yet, there are numerous instances in the literature where V. dahliae has been isolated from asymptomatic plants; thus, these plants should be considered hosts. In this article, we synthesize scattered research that indicates that V. dahliae, aside from being a successful and significant vascular plant pathogen, may have a cryptic biology on numerous asymptomatic plants as an endophyte. Thus, we suggest here that these endophytic associations among V. dahliae and asymptomatic plants are not unusual relationships in nature. We propose to embrace the broader ecology of many fungi by differentiating between "symptomatic hosts" as those plants in which the infection and colonization by a fungus results in disease, and "asymptomatic hosts" as those plants that harbor the fungus endophytically and are different than true nonhosts that should be used for plant species that do not interact with the given fungus. In fact, if we broaden our definition of "host plant" to include asymptomatic plants that harbor the fungus as an endophyte, it is likely that the host ranges for some soilborne fungal pathogens are much larger than previously envisioned. By ignoring the potential for soilborne fungal pathogens to display endophytic relationships, we leave gaps in our knowledge about the population biology and ecology, persistence, and spread of these fungi in agroecosystems.

On the reliability of DNA sequences of Ophiocordyceps sinensis in public databases

Some DNA sequences in the International Nucleotide Sequence Databases (INSD) are erroneously annotated, which has lead to misleading conclusions in publications. Ophiocordyceps sinensis (syn. Cordyceps sinensis) is a fungus endemic to the Tibetan Plateau, and more than 100 populations covering almost its distribution area have been examined by us over recent years. In this study, using the data from authentic materials, we have evaluated the reliability of nucleotide sequences annotated as O. sinensis in the INSD. As of October 15, 2012, the INSD contained 874 records annotated as O. sinensis, including 555 records representing nuclear ribosomal DNA (63.5 %), 197 representing protein-coding genes (22.5 %), 92 representing random markers with unknown functions (10.5 %), and 30 representing microsatellite loci (3.5 %). Our analysis indicated that 39 of the 397 internal transcribed spacer entries, 27 of the 105 small subunit entries, and five of the 53 large subunit entries were incorrectly annotated as belonging to O. sinensis. For protein-coding sequences, all records of serine protease genes, the mating-type gene MAT1-2-1, the DNA lyase gene, the two largest subunits of RNA polymerase II, and elongation factor-1α gene were correct, while 14 of the 73 β-tubulin entries were indeterminate. Genetic diversity analyses using those sequences correctly identified as O. sinensis revealed significant genetic differentiation in the fungus although the extent of genetic differentiation varied with the gene. The relationship between O. sinensis and some other related fungal taxa is also discussed.

Neighboring Deschampsia flexuosa and Trientalis europaea harbor contrasting root fungal endophytic communities

Fungal endophytic communities and potential host preference of root-inhabiting fungi of boreal forest understory plants are poorly known. The objective of this study was to find out whether two neighboring plant species, Deschampsia flexuosa (Poaceae) and Trientalis europaea (Primulaceae), share similar root fungal endophytic communities and whether the communities differ between two sites. The study was carried out by analysis of pure culture isolates and root fungal colonization percentages. A total of 84 isolates from D. flexuosa and 27 isolates from T. europaea were obtained. The roots of D. flexuosa harbored 16 different isolate types based on macromorphological characteristics, whereas only 4 isolate types were found in T. europaea. The root colonization by dark septate and hyaline septate hyphae correlated with isolate numbers being higher in D. flexuosa compared to T. europaea. The different isolate types were further identified on the basis of internal transcribed spacer sequence and phylogenetic analysis. An isolate type identified as dark septate endophyte Phialocephala fortinii colonized 50 % of the T. europaea and 21 % of the D. flexuosa specimens. In addition, Meliniomyces variabilis, Phialocephala sphaeroides, and Umbelopsis isabellina were found colonizing the grass, D. flexuosa, for the first time and Mycena sp. was confirmed as an endophyte of D. flexuosa. Site-specific differences were observed in the abundance and diversity of endophytic fungi in the roots of both study plants, but the differences were not as predominant as those between plant species. It is concluded that D. flexuosa harbors both higher amount and more diverse community of endophytic fungi in its roots compared to T. europaea.

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.

Fungi associated with the southern Eurasian orchid Spiranthes spiralis (L.) Chevall

The hitherto unknown relationships between the European orchid Spiranthes spiralis (L.) Chevall and its internally associated fungi were explored by a combined approach involving microscopy-based investigations at a morpho-histological level as well as by molecular analyses of the identity of the eukaryotic endophytes present in the root tissue of the plant. We found that this orchid which is currently reported to have a vulnerable status in northern Italy, can host and interact with at least nine types of fungi. Some of these fungi show similarity to mycorrhizal genera found in orchids such as the Ceratobasidium-Rhizoctonia group. Other fungi found are from the genera Davidiella (Ascomycota), Leptosphaeria (Ascomycota), Alternaria (Ascomycota), and Malassezia (Basidiomycota), some of which until have not previously been reported to have an endophytic relationship with plants. The repeated occurrence of often pathogenic fungi such as Fusarium oxysporum, Bionectria ochroleuca, and Alternaria sp., within healthy specimens of this orchid suggests a tempered interaction with species that are sometimes deleterious to non-orchid plants. The fact is reminiscent of the symbiotic compromise established by orchids with fungi of the rhizoctonia group.

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.