Dark Septate Endophytes Strains Research Articles

Study on the Biological Characteristics of Dark Septate Endophytes under Drought and Cadmium Stress and Their Effects on Regulating the Stress Resistance of Astragalus membranaceus.

Astragalus membranaceus is a famous traditional medicinal plant. However, drought and cadmium (Cd) pollution are the main abiotic stress factors that affect plant growth and yield and the ability to improve the host's stress resistance through the use of beneficial endophytic fungi. To evaluate the tolerance of dark septate endophytes (DSE) to various abiotic stresses, 10 DSE strains [Microsphaeropsis cytisi (Mc), Alternaria alstroemeriae (Aa), Stagonosporopsis lupini (Sl), Neocamarosporium phragmitis (Np), Paraphoma chlamydocopiosa (Pc), Macrophomina phaseolina (Mp'), Papulaspora equi (Pe), Alternaria tellustris (At), Macrophomina pseudophaseolina (Mp), and Paraphoma radicina (Pr)] were investigated under different drought and Cd stressors in vitro by using solid-plate cultures and liquid-shaker cultures in the current study. The experiments involved using varying concentrations of PEG (0, 9, 18, and 27%) and Cd2+ (0, 25, 50, and 100 mg/L) to simulate different stress conditions on DSE. Additionally, the effect of DSE (Np and At) on the growth of A. membranaceus at different field water capacities (70% and 40%) and at different CdCl2 concentrations (0, 5, 10, and 15 mg Cd/kg) in soil was studied. The results demonstrated that the colony growth rates of Aa, Np, Pc, Mp', and Mp were the first to reach the maximum diameter at a PEG concentration of 18%. Aa, Np, and At remained growth-active at 100 mg Cd/L. In addition, Aa, Np, and At were selected for drought and Cd stress tests. The results of the drought-combined-with-Cd-stress solid culture indicated that the growth rate of Np was significantly superior to that of the other strains. In the liquid culture condition, the biomasses of Np and Aa were the highest, with biomasses of 1.39 g and 1.23 g under the concentration of 18% + 25 mg Cd/L, and At had the highest biomass of 1.71 g at 18% + 50 mg Cd/L concentration, respectively. The CAT and POD activities of Np reached their peak levels at concentrations of 27% + 50 mg Cd/L and 27% + 25 mg Cd/L, respectively. Compared to the control, these levels indicated increases of 416.97% and 573.12%, respectively. Aa, Np, and At positively influenced SOD activity. The glutathione (GSH) contents of Aa, Np, and At were increased under different combined stressors of drought and Cd. The structural-equation-modeling (SEM) analysis revealed that Aa positively influenced biomass and negatively affected Cd content, while Np and At positively influenced Cd content. Under the stress of 40% field-water capacity and the synergistic stress of 40% field-water capacity and 5 mg Cd/kg soil, Np and At significantly increased root weight of A. membranaceus. This study provides guidance for the establishment of agricultural planting systems and has good development and utilization value.

Fostering Growth in Cinnamomum kanehirae Cuttings: The Beneficial Role of Dark Septate Endophytes in Forest Nursery Management

Root development is critical to successful establishment after seedlings are out-planted on a forest restoration site. However, the restoration of an endangered Cinnamomum kanehirae using cuttings was limited by the lack of axial roots. Dark septate endophytes (DSEs) are an important group of asexual filamentous ascomycetous fungi and could promote the performance of host plants. In the current study, we explored the effects of four DSE strains (Melnikomyces sp., Acrocalymma vagum, Wiesneriomyces sp., and Tricholomataceae sp.) on the growth of C. kanehirae cuttings under nursery conditions. The results show that four DSE isolates are able to form symbiotic relationships with C. kanehira, enhancing the seedling height, fresh weight, and chlorophyll concentrations. Notably, the Melnikomyces sp. (DB5) showed significant improvements, secreting peroxidase and indole acetic acid. To facilitate the detection of DB5 within the host roots, we developed specific primers (DB5-1F/DB5-1R). We recommend the adoption of the endophyte inoculation approach and molecular detection methods in forestry nurseries as valuable tools to enhance silvicultural practices and contribute to the conservation of C. kanehirae.

Temporal and spatial dynamics and functional metabolism of dark septate endophytes of Gymnocarpos przewalskii Maxim. in Northwest Desert, China

In extreme habitats, plants can survive mutually with their beneficial colony partners. How dark septate endophytes (DSE) assist the relict plant Gymnocarpos przewalskii survive in extremely desert environment and maintain the stability of the ecosystem remains unclear. Studying distribution, seasonal changes and functional physiological responses of DSE colonized in roots of G. przewalskii can help understand symbiosis mechanism of these endophytes associated to relict plants in extremely arid desert environments. DSE colonization, species diversity and soil properties of G. przewalskii were measured in Anxi and Minqin sites, Northwest China in July, September and December 2019. Subsequently, the functional metabolism of DSE strain was measured, and the response of DSE strain to drought stress was performed in vitro. DSE hyphal colonization (23.3 % - 39.2 %) and DSE isolation frequency (6.0 % - 27.6 %) varied sharply among seasons and sites. Soil alkaline phosphatase, nitrate nitrogen and total phosphorus were main factors affecting the DSE composition. Twenty-six DSE isolates produced indole-3-acetic acid (IAA) in the medium, while 50 % of DSE showed a potential for IAA production in L-tryptophan-dependent. Additionally, the composition of functional metabolites of DSE strains varied greatly with different drought levels and DSE isolates, which may indirectly reflect the complementarity between different strains in helping hosts cope with drought stress. This study confirmed the temporal and spatial dynamics and growth-promoting and drought-tolerant potential of DSE community in desert environment, and provided a new perspective for exploring the survival strategy and vegetation protection of desert relict plants.

Occurrence of dark septate endophytes in Phragmites australis in the Baiyang Lake and their resistance to Cd stress

Heavy metal pollution poses a serious hazard to human health, and microbial remediation of heavy metals in soil has been widely studied. A group of ascomycetes classified as dark septate endophytes (DSEs) colonize plant roots and benefit host plants under abiotic stress conditions. In this study, Phragmites australis, a common remediation plant in Baiyang Lake, was investigated. The root system and soil of P. australis were collected in typical heavy metal-contaminated sites, and the species diversity and community structure of DSEs in P. australis roots were studied. In addition, DSE strains were isolated, cultured, and tested for their tolerance to Cd stress. The results showed that DSEs occur extensively in P. australis roots, forming typical dark septate hyphae, with a total colonization rate of 19.7–83.1%. Morphological and ITS sequencing analyses were used to identify 10 DSE fungi in 9 genera. Among these fungi, 6 strains with considerable resistance to Cd stress were identified. The biomass values of Poaceascoma helicoides, Alternaria doliconidium, and Acrocalymma vagum strains increased as the Cd concentration increased. These results can not only help to understand plant-DSE interactions in wetland environments, but also provide a theoretical basis for making full use of DSE fungi to alleviate heavy metals in soil.

Impact of dark septate endophytes on salt stress alleviation of tomato plants.

Fungal endophytes can improve plant tolerance to abiotic stress conditions. Dark septate endophytes (DSEs) belong to phylogenetically non-related groups of root colonizing fungi among the Ascomycota with high melanin-producing activities. They can be isolated from roots of more than 600 plant species in diverse ecosystems. Still the knowledge about their interaction with host plants and their contribution to stress alleviation is limited. The current work aimed to test the abilities of three DSEs (Periconia macrospinosa, Cadophora sp., Leptodontidium sp.) to alleviate moderate and high salt stress in tomato plants. By including an albino mutant, the role of melanin for the interaction with plants and salt stress alleviation could also be tested. P. macrospinosa and Cadophora sp. improved shoot and root growth 6 weeks after inoculation under moderate and high salt stress conditions. No matter how much salt stress was applied, macroelement (P, N, and C) contents were unaffected by DSE inoculation. The four tested DSE strains successfully colonized the roots of tomato, but the colonization level was clearly reduced in the albino mutant of Leptodontidium sp. Any difference in the effects on plant growth between the Leptodontidium sp. wild type strain and the albino mutant could, however, not be observed. These results show that particular DSEs are able to increase salt tolerance as they promote plant growth specifically under stress condition. Increased plant biomasses combined with stable nutrient contents resulted in higher P uptake in shoots of inoculated plants at moderate and high salt conditions and higher N uptake in the absence of salt stress in all inoculated plants, in P. macrospinosa-inoculated plants at moderate salt condition and in all inoculated plants except the albino mutants at high salt condition. In summary, melanin in DSEs seems to be important for the colonization process, but does not influence growth, nutrient uptake or salt tolerance of plants.

Relationship of root dark septate endophytes and soil factors to plant species and seasonal variation in extremely arid desert in Northwest China

Investigations on host affiliations, seasonal variation and physiological response to drought tolerance of dark septate endophytes (DSE) in extremely arid desert environments can help explain the adaptive mechanisms of these endophytes in desert ecosystems. The colonization and species diversity of DSE and the soil factors in the rhizospheres of five desert shrubs were therefore determined in Anxi extremely arid environment in Northwest China in July, September and December 2020. Subsequently, six DSE strains were selected to test the growth and metabolic response of DSE strains to drought stress in vitro. The sampled plants and seasons significantly influenced the morphology, colonization and species diversity of DSE. Of the 15 DSE species isolated in the roots of these plants, Triangularia allahabadensis was reported in desert ecosystems for the first time. DSE colonization was predominately affected by season and soil factors, while species composition was more corresponded to plant species. The composition of metabolites of DSE strains varied significantly due to levels of drought stress and DSE identity, which indirectly reflected the difference of their traits to respond to drought stress. This study confirmed the establishment of relationship between DSE and roots of xerophytic plants, and proved the drought tolerance of DSE in vitro, providing insight into the application of DSE to assist desert plants to resist drought.

Antagonistic capacity of dark septate endophytes (DSE) against Ganoderma boninense from oil palm (Elaeis guinensis Jacq.)

Ganoderma boninense, a causal agent of basal stem rot, as one of the major problems in oil palm plantation in Indonesia. The potential of dark septate endophytes (DSE) as biocontrol agents for G. boninense is not widely studied. Therefore, this study aims to screen DSE strains to obtain high antagonistic strains. The antagonistic capacity of 10 DSE strains was determined based on the growth inhibition in the dual culture, and volatile compounds challenge against G. boninense, in vitro. Volatile compound profiling of selected DSE strains that showed the highest challenge capacity was done using Pyrolysis Gas Chromatography-Mass Spectrometry. Among 10 DSE strains tested, TKC 2.2a had the highest percentage of G. boninense inhibition in dual cultures and the volatile compound challenge. This strain inhibited better if grown in media seven days earlier than grown simultaneously with G. boninsense. The volatile compounds of 14 days old TKC 2.2a were of 2H-1-Benzopyran-7-ol, 3,4-dihydro-5-methoxy-6-methyl-2-phenyl; 4-Allyl-2,6-dimetho-xyphenol; and hexa-decanoic acid, which were reported as having either antimicrobial or antifungal activities. These results indicate that DSE TKC 2.2a can be a candidate for a biocontrol agent against G. boninense in oil palm, depending on further research on its ability to reduce basal stem rot symptoms.

Decolourization of congo red synthetic dyes by dark septate endophytes

The use of fungi is known to be an eco-friendly and cost-competitive approach to degrade synthetic dyes such as Congo Red (CR) in industrial effluents. This research aimed to evaluate the potential of dark septate endophytes (DSE) fungi in decolourizing CR synthetic dyes. Two DSE strains, namely CPP and KSP, were studied to decolourize 50 mgL−1 CR based on the capability to produce the ligninolytic enzyme, dye decolourization efficiency, decolourization index, and fungal dry biomass weight after 7 and 14 days of incubation. CR decolourization was monitored spectrophotometry at 495 nm. The result indicated that CPP and KSP were successfully decolourized CR dye up to 97.00% and 85.00%, respectively, with decolourization index of 1.37 and 1.36 within 14 days. There is no significant difference in DSE growth with and without the addition of CR dye. In addition, these two DSE fungi (CPP and KSP) are able to produce ligninolytic enzymes. The results indicated that the DSE are potential to be used as decolourization agents for azo synthetic dyes. This is the first report on the ability of DSE to decolourize azo synthetic dyes.

Isolation, identification, and characterization of cadmium-tolerant endophytic fungi isolated from barley (Hordeum vulgare L.) roots and their role in enhancing phytoremediation.

Four hundred endophytic fungi isolates with different colony morphologies were isolated from roots of Hordeum vulgare L. collected from un-engineered landfills (the measured cadmium was 0.9 mg kg-1) of Kermanshah province in West Iran. Based on morphology and phylogeny of DNA sequence data for the internal transcribed spacer (ITS) rDNA and comparing the sequences with that available in NCBI database, 11 isolates are identified as dark septate endophytes (DSE) including Alternaria alternata, Microdochium bolleyi, Bipolaris zeicola, Alternaria sp., and Pleosporales sp., and the other nine are not dark septate endophytes (non-DSE) including Fusarium redolens, Fusarium tricinctum, Fusarium monliforme, Clonostachys rosea, and Epicoccum nigrum. Tolerance of DSE and non-DSE strains for Cd were investigated in potato dextrose agar medium. Minimum inhibitory concentrations (MIC) of Cd from nitrate salt source (Cd (NO3)2) and EC50 were determined. The means of MIC and EC50 values for DSE fungi species were 1254.5 and 209.74 mg/kg, compared to 800 and 150.3 mg/kg for non-DSEs. Among the endophytic fungi isolated, Alternaria sp. (TBR5) and Bipolaris zeicola (Tw26) showed the highest tolerance to Cd with a MIC value of 2000 mg/L and 1800 mg/L, respectively. Barley plants were inoculated with TBR5 and Tw26 in Cd-added sands (0, 10, 30, 60 mg Cd/kg sand). In terms of Cd accumulation, our results showed that TBR5 and Tw26 inoculation increased the amount of Cd in the barley roots. TBR5 and Tw26 significantly improved (p < 0.05) plant growth in the presence of Cd by enhancing plant growth attributes such as chlorophyll content, root weight, plant length, fresh weight, and dry weight of plants. This is the first study on the abundance and identification of endophytic root fungi of barley in a cadmium-contaminated soil in Iran. The results of this study showed that DSE and non-DSE have the potential to improve the efficiency of phytoremediation.

Effect of dark septate endophytes on plant performance of Artemisia ordosica and associated soil microbial functional group abundance under salt stress

Fungal endophytes can improve plant tolerance to abiotic stress, however, the role of these plant–fungal interactions in desert species ecology and their management implications remain unclear. This study aimed to assess the effects of dark septate endophytes (DSE) on the performance of Artemisia ordosica and associated soil factors and microbial functional group abundance under salt stress. We investigated the effects of three DSE (Alternaria chlamydosporigena [AC], Paraphoma chrysanthemicola [PC] and Bipolaris sorokiniana [BS]) isolated from desert habitats on plant morphology, physiology and rhizosphere soil microhabitat of A. ordosica seedlings under different NaCl concentrations (0, 1, 2, 3 g NaCl/kg soil) in a growth chamber. The three DSE strains could colonize the roots of A. ordosica, and the symbiotic response with host plants depended on DSE species and NaCl concentration. The greatest benefits associated with DSE occurred under 1 g NaCl/kg soil. Specifically, AC promoted the accumulation of total biomass and enhanced superoxide dismutase (SOD) activity; PC promoted the accumulation of root biomass and increased indoleacetic acid (IAA) contents; and BS enhanced SOD activity and glutathione (GSH) and IAA contents. DSE reduced the root Na+ content. Interestingly, BS promoted gram-positive (G +) under 1 g NaCl/kg soil and the abundance of arbuscular mycorrhizal (AM) fungi under 3 g NaCl/kg soil. PC positively affected fungi, AM fungi, gram-negative (G −) bacteria and actinomycetes under 2 g NaCl/kg soil, and increased AM fungi and G – bacteria under 3 g NaCl/kg soil, while AC increased the abundance of all examined microbes under 3 g NaCl/kg soil. Structural equation modeling (SEM) demonstrated that DSE inoculation significantly influenced the relationship between the growth of A. ordosica, soil factors and rhizospheric microbial functional groups under NaCl stress treatments. DSE enhanced the root development of host plants and altered the soil nutrient content and microbiota under different NaCl concentrations, possibly contributing to plant growth and ecological adaptability under saline environment. These results contribute to the understanding of ecological function of DSE inoculation in improving the adaptability of plants to salt stress and may be used to promote vegetation restoration in salinized desert areas.

Colonization by dark septate endophytes improves the growth and rhizosphere soil microbiome of licorice plants under different water treatments

Dark septate endophytes (DSE) are facultative biotrophic ascomycetes that colonize plant roots. DSE may provide nutrients to their plant hosts and help them adapt to various abiotic and biotic stresses. However, their effects on the microbiome composition in plant rhizosphere need further clarification. Here, we conducted a pot experiment to establish whether the responses of licorice (Glycyrrhiza uralensis) to DSE (Acrocalymma vagum, Paraboeremia putaminum) inoculation under different water treatments are caused by changes in the rhizosphere microbiome. Rhizosphere microbiome compositions were measured by Illumina MiSeq sequencing of the 16S and ITS2 rRNA genes. The inoculation with DSE strains had a positive effect on plant growth of licorice depending on DSE species and water treatments. Subsequently, a total of 1278 fungal and 1583 bacterial operational taxonomic units (OUTs) were obtained at a 97% sequence similarity level. Ascomycota were the predominant fungi and Proteobacteria, Actinobacteria, Chloroflexi and Firmicutes were the predominant bacteria. DSE inoculation and water regime significantly influenced the microbiome composition. However, the effects of DSE on the fungal community were greater than those on the bacterial community. P. putaminum exerted a stronger impact on the licorice rhizosphere microbiome than A. vagum under drought stress. The observed changes in edaphic factors (water condition, soil organic matter, available nitrogen, available phosphorus, and available potassium) caused by DSE inoculation could be explained by the variations in microbiome composition. A network analysis indicated that DSE inoculation augmented the relative abundance of beneficial symbiotrophic fungi and growth-promoting bacteria but diminished the relative abundance of pathogens in the licorice rhizosphere. The present study showed that the licorice rhizosphere microbial community differed between the DSE-inoculated and uninoculated plants. DSE had a stronger influence on the fungal than on the bacterial rhizosphere community under drought stress. These give us the guidance to develop biofertilizers with DSE consortia to enhance the cultivation of medicinal plants by shaping soil microbial community structure and soil nutrient status in dryland agriculture.

Dark septate endophytes isolated from non-hyperaccumulator plants can increase phytoextraction of Cd and Zn by the hyperaccumulator Noccaea caerulescens.

Dark septate endophytes (DSEs) can improve plant stress tolerance by promoting growth and affecting element accumulation. Due to its ability to accumulate high Cd, Zn, and Ni concentrations in its shoots, Noccaea caerulescens is considered a promising candidate for phytoextraction in the field. However, the ability of DSEs to improve trace element (TE) phytoextraction with N. caerulescens has not yet been studied. The aim of this study was therefore to determine the ability of five DSE strains, previously isolated from poplar roots collected at different TE-contaminated sites, to improve plant development, mineral nutrient status, and metal accumulation by N. caerulescens during a pot experiment using two soils differing in their level of TE contamination. Microscopic observations revealed that the tested DSE strains effectively colonised the roots of N. caerulescens. In the highly contaminated (HC) soil, a threefold increase in root biomass was found in plants inoculated with the Leptodontidium sp. Pr30 strain compared to that in the non-inoculated condition; however, the plant nutrient status was not affected. In contrast, the two strains Phialophora mustea Pr27 and Leptodontidium sp. Me07 had positive effects on the mineral nutrient status of plants without significantly modifying their biomass. Compared to non-inoculated plants cultivated on HC soil, Pr27- and Pr30-inoculated plants extracted more Zn (+ 30%) and Cd (+ 90%), respectively. In conclusion, we demonstrated that the responses of N. caerulescens to DSE inoculation ranged from neutral to beneficial and we identified two strains (i.e. Leptodontidium sp. (Pr30) and Phialophora mustea (Pr27)) isolated from poplar that appeared promising as they increased the amounts of Zn and Cd extracted by improving plant growth and/or TE accumulation by N. caerulescens. These results generate interest in further characterising the DSEs that naturally colonise N. caerulescens and testing their ability to improve phytoextraction.

Dark Septate Endophytic Fungi Associated with Sugarcane Plants Cultivated in São Paulo, Brazil

Dark septate endophytes (DSEs) constitute a polyphyletic group within the Ascomycota, with global distribution and a wide range of host plant species. The present study evaluated the diversity of DSE in sugarcane roots of the varieties RB867515, RB966928, and RB92579, and four varieties of not commercialized energy cane. A total of 16 DSE strains were isolated, mostly from the varieties RB966928 and RB867515, with six and five isolates, respectively. Just one of the four energy cane varieties had fungi with DSE appearance. The analyses of the DNA sequences from the internal transcribed spacer (ITS) and the large subunit (LSU), in association with the micromorphology of the isolates, allowed the differentiation of the 16 isolates in at least five species, within the families Periconiaceae, Pleosporaceae, Lentitheciaceae, Vibrisseaceae, and Apiosporaceae and the orders Pleosporales, Helotiales, and Xylariales. The order Pleosporales represented 80% of the isolates, and the species Periconia macrospinosa, with six isolates, accounted for the highest isolation frequency. The results confirm the natural occurrence of the DSE symbiosis in sugarcane varieties and the generalist character of these fungi as some of the detected species have already been reported associated with other host plants, ecosystems, and regions of the world.

Plant performance of enhancing licorice with dual inoculating dark septate endophytes and Trichoderma viride mediated via effects on root development

BackgroundThis study aimed to assess whether licorice (Glycyrrhiza uralensis) can benefit from dual inoculation by Trichoderma viride and dark septate endophytes (DSE) isolated from other medicinal plants.MethodsFirst, we isolated and identified three DSE (Paraboeremia putaminum, Scytalidium lignicola, and Phoma herbarum) and Trichoderma viride from medicinal plants growing in farmland of China. Second, we investigated the influences of these three DSE on the performance of licorice at different T. viride densities (1 × 106, 1 × 107, and 1 × 108 CFU/mL) under sterilised condition in a growth chamber.ResultsThree DSE strains could colonize the roots of licorice, and they established a positive symbiosis with host plants depending on DSE species and T. viride densities. Inoculation of P. putaminum increased the root biomass, length, surface area, and root:shoot ratio. S. lignicola increased the root length, diameter and surface area and decreased the root:shoot ratio. P. herbarum increased the root biomass and surface area. T. viride increased the root biomass, length, and surface area. Structural equation model (SEM) analysis showed that DSE associated with T. viride augmented plant biomass and height, shoot branching, and root surface area. Variations in root morphology and biomass were attributed to differences in DSE species and T. viride density among treatments. P. putaminum or P. herbarum with low- or medium T. viride density and S. lignicola with low- or high T. viride density improved licorice root morphology and biomass.ConclusionsDSE isolated from other medicinal plants enhanced the root growth of licorice plants under different densities T. viride conditions and may also be used to promote the cultivation of medicinal plants.

Effects of enhancement of liquorice plants with dark septate endophytes on the root growth, glycyrrhizic acid and glycyrrhizin accumulation amended with organic residues

Dark septate endophytes (DSE) is a diverse group of Ascomycetes fungi involved in a mutualistic symbiosis with plant roots, however, their ecological roles need further clarification. This study aimed to investigate how DSE (Acrocalymma vagum and Paraboeremia putaminum) affect liquorice (Glycyrrhiza uralensis) growth under additional sterilized fermented and unfermented organic residues. Two DSE strains could establish a positive symbiosis with the host plants depending on DSE species and residue availability. Specifically, A. vagum inoculation mainly promoted the development of lateral roots, whereas P. putaminum inoculation mainly improved the taproot development. Mantel test and structural equation model (SEM) analysis demonstrated that DSE associated with residues significantly positively influenced the plant biomass, taproot length, total root length, root diameter, glycyrrhizic acid and glycyrrhizin content. The greatest benefits of DSE inoculation occurred in fermented residue treatment. Variation in root growth can be attributed to the effects of DSE inoculation. As A. vagum exhibited positive effects on the plant biomass, root growth, and active ingredient content in liquorice plants under organic residues treatment, it was considered to be the best combination of A. vagum and fermented residues for the liquorice cultivation. These results contribute to the understanding of the ecological function of DSE fungi in nutrient deficiency lands.

Plant Growth and Soil Microbial Impacts of Enhancing Licorice With Inoculating Dark Septate Endophytes Under Drought Stress.

This study mainly aimed to investigate the effects of dark septate endophytes (DSE) (Acrocalymma vagum, Paraboeremia putaminum, and Fusarium acuminatum) on the growth and microbial community composition in the rhizosphere soil of a medicinal plant, licorice (Glycyrrhiza uralensis), grown in the non-sterile soil under drought stress. The results showed that three DSE strains could effectively colonize the plant roots and form a strain-dependent symbiosis with licorice. Although drought stress declined the growth of licorice plants, these decreases were partly recovered by DSE inoculation. Specifically, the inoculation of A. vagum and P. putaminum significantly increased the biomass and glycyrrhizin content, whereas A. vagum and F. acuminatum increased glycyrrhizic acid content of host plants under drought stress. However, the inoculation of F. acuminatum showed significant negative effects on the shoot, root, and total biomass of licorice plants. In addition, the effects of DSE inoculation on the morphological, photosynthetic, and antioxidant parameters of licorice plants, and mineral nutrient and microbial community composition in the rhizosphere soil were dependent on the DSE species as well as water regime. Interestingly, DSE inoculation significantly increased AM fungi content under drought stress. In addition, DSE associated with water had a significant positive influence on soil organic matter, available phosphorus (P), AM fungi, leaf number, soluble protein, SOD activity, total root length, root branch, and glycyrrhizic acid content. Based on the results of variance partitioning analysis, 17.0, 34.0, 14.9, 40.1, 28.2, and 18.0% variations in shoot morphology, root morphology, plant biomass, active ingredient, photosynthetic parameters, and antioxidant parameters, respectively, were attributable to the presence of certain soil microorganisms. These findings suggest the possibility that DSE inoculation improved the root development and nutrient absorption of host plants, altered the soil microbiota, and might also contribute to plant growth and survival under drought conditions. As A. vagum exhibited positive effects on the plant biomass, morphological and physiological parameters, and active ingredient content in licorice plants under drought stress, it was considered to be the best fungus for licorice cultivation. These results contribute to the understanding of the ecological function of DSE fungi in dryland agriculture.

Effects of Dark Septate Endophytes on the Performance of Hedysarum scoparium Under Water Deficit Stress.

Hedysarum scoparium, a species characterized by rapid growth and high drought resistance, has been used widely for vegetative restoration of arid regions in Northwest China that are prone to desertification. Desert soil is typically deficient in available water and the alleviation of drought stress to host plants by endophytes could be an efficient strategy to increase the success of desert restoration. With the objective to seek more beneficial symbionts that can be used in the revegetation strategies, we addressed the question whether H. scoparium can benefit from inoculation by dark septate endophytes (DSEs) isolated from other desert plants. We investigated the influences of four non-host DSE strains (Phialophora sp., Knufia sp., Leptosphaeria sp., and Embellisia chlamydospora) isolated from other desert plants on the performance of H. scoparium under different soil water conditions. Differences in plant performance, such as plant growth, antioxidant enzyme activities, carbon, nitrogen, and phosphorous concentration under all the treatments, were examined. Four DSE strains could colonize the roots of H. scoparium successfully, and they established a positive symbiosis with the host plants depending on DSE species and water availability. The greatest benefits of DSE inoculation occurred in water stress treatment. Specifically, Phialophora sp. and Leptosphaeria sp. improved the root biomass, total biomass, nutrient concentration, and antioxidant enzyme activities of host plants under water deficit conditions. These data contribute to the understanding of the ecological function of DSE fungi in drylands.

Dark septate endophytes isolated from a xerophyte plant promote the growth of Ammopiptanthus mongolicus under drought condition

Dark septate endophytes (DSE) may facilitate plant growth and stress tolerance in stressful ecosystems. However, little is known about the response of plants to non-host DSE fungi isolated from other plants, especially under drought condition. This study aimed to seek and apply non-host DSE to evaluate their growth promoting effects in a desert species, Ammopiptanthus mongolicus, under drought condition. Nine DSE strains isolated from a super-xerophytic shrub, Gymnocarpos przewalskii, were identified and used as the non-host DSE. And DSE colonization rate (30–35%) and species composition in the roots of G. przewalskii were first reported. The inoculation results showed that all DSE strains were effective colonizers and formed a strain-dependent symbiosis with A. mongolicus. Specifically, one Darksidea strain, Knufia sp., and Leptosphaeria sp. increased the total biomass of A. mongolicus compared to non-inoculated plants. Two Paraconiothyrium strains, Phialophora sp., and Embellisia chlamydospora exhibited significantly positive effects on plant branch number, potassium and calcium content. Two Paraconiothyrium and Darksidea strains particularly decreased plant biomass or element content. As A. mongolicus plays important roles in fixing moving sand and delay desertification, the ability of certain DSE strains to promote desert plant growth indicates their potential use for vegetation recovery in arid environments.

Melanization and ageing are not drawbacks for successful agro-transformation of dark septate endophytes

Dark septate endophytes (DSEs) are melanin-enriched ascomycetous fungi that are abundant in stressed environments. However, little is known about their physiology and metabolism, and DSE genes have not been functionally characterized yet. Therefore developing molecular genetic tools to investigate the biological function of genes of interest in DSEs is of major significance. We investigated Agrobacterium tumefaciens-mediated transformation (ATMT) efficiency in eight DSE strains belonging to Cadophora sp., Cadophora malorum, Leptodontidium sp., Phialophora mustea, and Cladosporium cladosporioides. ATMT efficiency was DSE-dependent and ranged from 0.6 to 125 %. We further focused on the effect of mycelium ageing on ATMT efficiency. Leptodontidium sp. Me07, Leptodontidium sp. Pr30, and C. cladosporioides CBS 101367 were significantly more transformed using 15-d-old mycelium (44.5, 6.9, and 1.1 %, respectively) as compared to 2-d-old mycelium (121, 28.7, and 25.1, respectively), whereas P. mustea Pr29 was more transformed using young mycelium (21.5 % compared to 5.3 % for the old mycelium). Finally, we focused on the effect of melanin content on ATMT efficiency. Melanin content in mycelium ranged from 0.9 to 3.2 mg g−1 DW. Tricyclazole negatively modulated melanin content, while copper positively modulated it. However there was no correlation between hyphal melanin content and ATMT efficiency.

Dark septate endophytes present different potential to solubilize calcium, iron and aluminum phosphates

Many microorganisms play a significant role in releasing phosphorus (P) from soil insoluble phosphates to crops. Here, we evaluated the ability of dark septate endophytes (DSE) to solubilize calcium, aluminum and iron phosphates. DSE were isolated from the roots of wheat (Triticum aestivum) and the forages Panicum coloratum and Chloris gayana, which are grown in slightly acidic and alkaline soils of the Argentine Pampas, respectively. Protocols to corroborate their endophytic nature were followed. Nine fungi were identified by morphological and molecular characteristics, and their sequences were deposited in GenBank. The isolates belonged to the same order and genera as DSE fungi recorded in other parts of the world. The temperature and pH requirements of the DSE strains were verified. To determine their ability to solubilize phosphate, we followed two in vitro methodologies: solid and liquid media. On solid medium, all isolates showed ability to solubilize calcium phosphate, three strains solubilized aluminum phosphate, and none of them solubilized iron phosphate. The DSE most efficient in solubilizing calcium phosphate were Ophiosphaerella sp. and Cochliobolus sp., followed by Setosphaeria rostrata. The strains Drechslera sp. (P6), Ophiosphaerella herpotricha and Drechslera sp. (12–15) were able to solubilize aluminum phosphate. In liquid medium, the isolates showed different ability to generate acidity and to solubilize phosphates. Drechslera sp. (12–15) was among the most efficient in solubilizing calcium phosphate, Curvularia sp. in solubilizing aluminum phosphate and Ophiosphaerella sp. in solubilizing iron phosphate. The results obtained combining both methodologies indicate that S. rostrata was not the best with each phosphate individually but showed the best global performance. DSE fungi are far less identified than other groups of fungi and bacteria as soil insoluble phosphate-solubilizing agents. However, they showed potential for application as biofertilizers in different soils to manage sustainable agroecosystems.