Does water availability influence the abundance of species of the Phialocephala fortinii s.l. – Acephala applanata complex (PAC) in roots of pubescent oak (Quercus pubescens) and Scots pine (Pinus sylvestris)?

Importance of Dark Septate Endophytes in Agriculture in the Face of Climate Change

Climate change is a notable challenge for agriculture as it affects crop productivity and yield. Increases in droughts, salinity, and soil degradation are some of the major consequences of climate change. The use of microorganisms has emerged as an alternative to mitigate the effects of climate change. Among these microorganisms, dark septate endophytes (DSEs) have garnered increasing attention in recent years. Dark septate endophytes have shown a capacity for mitigating and reducing the harmful effects of climate change in agriculture, such as salinity, drought, and the reduced nutrient availability in the soil. Various studies show that their association with plants helps to reduce the harmful effects of abiotic stresses and increases the nutrient availability, enabling the plants to thrive under adverse conditions. In this study, the effect of DSEs and the underlying mechanisms that help plants to develop a higher tolerance to climate change were reviewed.

The Role of Phialocephala fortinii in Improving Plants' Phosphorus Nutrition: New Puzzle Pieces

Plants' mineral nutrition in acidic soils can be facilitated by phosphate solubilizing fungi inhabiting the root systems of these plants. We attempt to find dark septate endophyte (DSE) isolates in the roots of wild-heather plants, which are capable of improving plants' phosphorus nutrition levels. Bright-field and confocal laser scanning microscopy were used for the visualization of endophytes. A model system of co-cultivation with Vaccinium macrocarpon Ait. was used to study a fungal isolate's ability to supply plants with phosphorus. Fungal phytase activity and phosphorus content in plants were estimated spectrophotometrically. In V. vitis-idaea L. roots, we obtained a Phialocephala fortinii Wang, Wilcox DSE2 isolate with acid phytase activity (maximum 6.91 ± 0.17 U on 21st day of cultivation on potato-dextrose broth medium) and the ability to accumulate polyphosphates in hyphae cells. The ability of the isolate to increase both phosphorus accumulation and biomass in V. macrocarpon is also shown. The data obtained for the same isolate, as puzzle pieces put together, indicate the possible mediation of P. fortinii DSE2 isolate in the process of phosphorus intake from inorganic soil reserves to plants.

Effects of nitrogen addition and root fungal inoculation on the seedling growth and rhizosphere soil microbial community of Pinus tabulaeformis

Nitrogen (N) availability is significant in different ecosystems, but the response of forest plant-microbial symbionts to global N deposition remains largely unexplored. In this study, the effects of different N concentration levels on four types of fungi, Suillus granulatus (Sg), Pisolithus tinctorius (Pt), Pleotrichocladium opacum (Po), and Pseudopyrenochaeta sp. (Ps), isolated from the roots of Pinus tabulaeformis were investigated in vitro. Then, the effects of the fungi on the growth performance, nutrient uptake, and rhizosphere soil microbial community structure of P. tabulaeformis under different N addition conditions (0, 40, and 80 kg hm⁻² year⁻¹) were examined. The biomass and phytohormone contents of the Sg, Pt and Po strains increased with increasing N concentration, while those of the Ps strain first increased and then decreased. All four fungal strains could effectively colonize the plant roots and form a strain-dependent symbiosis with P. tabulaeformis. Although the effects depended on the fungal species, the growth and root development of inoculated seedlings were higher than those of uninoculated seedlings under N deficiency and normal N supply conditions. However, these positive effects disappeared and even became negative under high N supply conditions. The inoculation of the four fungal strains also showed significant positive effects on the shoot and root nutrient contents of P. tabulaeformis. Fungal inoculation significantly increased different microbial groups and the total soil microorganisms but decreased the microbial diversity under N deficiency stress. In summary, exogenous symbiotic fungal inoculations could increase the growth performance of P. tabulaeformis under N deficiency and normal N supply conditions, but the effects were negative under excessive N addition.

Improved Tolerance of Artemisia ordosica to Drought Stress via Dark Septate Endophyte (DSE) Symbiosis

Dark septate endophytes (DSEs) usually colonize plant roots, especially in stress environments. However, their relationship with plants ranges from beneficial to harmful and has remained largely uncharacterized. In the present study, 14 DSE species grouped into 11 genera were isolated from the roots of a desert plant, Artemisia ordosica, which is widely distributed in northwest China. Three dominant DSE species—Paraphoma chrysanthemicola (Pc), Alternaria chartarum (Ac), and Acrocalymma vagum (Av)—were selected and tested for their resistance to drought in vitro. Furthermore, we characterized the responses of A. ordosica under drought conditions in relation to the presence of these DSEs following inoculation. The results showed that all three strains grew well under in vitro drought stress, and the biomass of Ac and Av was significantly higher than that of the unstressed control. The effects of DSE inoculation on the growth of A. ordosica under drought stress varied according to the different DSE species but were generally beneficial. Under drought stress, Av and Pc promoted plant growth, antioxidant enzyme activity, and root development of the hosts. The Ac strain conferred obvious positive effects on the antioxidant enzyme activity of the hosts. In general, Av and Pc demonstrated better application potential for improving the drought resistance of A. ordosica.

Advances in the Role of Dark Septate Endophytes in the Plant Resistance to Abiotic and Biotic Stresses

Endophytic fungi have been studied in recent decades to understand how they interact with their hosts, the types of relationships they establish, and the potential effects of this interaction. Dark septate endophytes (DSE) are isolated from healthy plants and form melanised structures in the roots, including inter- and intracellular hyphae and microsclerotia, causing low host specificity and covering a wide geographic range. Many studies have revealed beneficial relationships between DSE and their hosts, such as enhanced plant growth, nutrient uptake, and resistance to biotic and abiotic stress. Furthermore, in recent decades, studies have revealed the ability of DSE to mitigate the negative effects of crop diseases, thereby highlighting DSE as potential biocontrol agents of plant diseases (BCAs). Given the importance of these fungi in nature, this article is a review of the role of DSE as BCAs. The findings of increasing numbers of studies on these fungi and their relationships with their plant hosts are also discussed to enable their use as a tool for the integrated management of crop diseases and pests.

Investigating Host Preference of Root Endophytes of Three European Tree Species, with a Focus on Members of the Phialocephala fortinii-Acephala applanata Species Complex (PAC)

Host preference of root endophytes of the three European tree species of Norway spruce (Picea abies), common ash (Fraxinus excelsior), and sycamore maple (Acer pseudoplatanus) were investigated in two forest stands near Zurich, Switzerland. The focus was placed on members of the Phialocephala fortinii s.l. (sensu lato)-Acephala applanata species complex (PAC), as well as other dark septate endopyhtes (DSE). PAC species were identified based on 13 microsatellite loci. Eleven PAC species were found, with Phialocephala helvetica, P. europaea being the most frequent. All but cryptic species 12 (CSP12) preferred Norway spruce as a host. Though very rare in general, CSP12 was most frequently isolated from maple roots. Regarding the abundant PAC species, P. helvetica and P. europaea, the preference of spruce as a host was least pronounced in P. europaea, as it was also often isolated from ash and maple. It is the first record of PAC found on common ash (Fraxinus excelsior). Cadophora orchidicola, a close relative of PAC, has frequently been isolated from ash. Various species of the Nectriaceae (Cylindrocarpon spp.) have often been isolated, particularly from maple roots. By comparison, Pezicula spp. (Cryptosporiopsis spp.) was found to be abundant on all three hosts. Phomopsis phaseoli exhibits a clear preference for spruce.

Mollisiaceae: An overlooked lineage of diverse endophytes

Mollisia is a taxonomically neglected discomycete genus (Helotiales, Leotiomycetes) of commonly encountered saprotrophs on decaying plant tissues throughout temperate regions. The combination of indistinct morphological characters, more than 700 names in the literature, and lack of reference DNA sequences presents a major challenge when working with Mollisia. Unidentified endophytes, including strains that produced antifungal or antiinsectan secondary metabolites, were isolated from conifer needles in New Brunswick and placed with uncertainty in Phialocephala and Mollisia, necessitating a more comprehensive treatment of these genera. In this study, morphology and multigene phylogenetic analyses were used to explore the taxonomy of Mollisiaceae, including Mollisia, Phialocephala, and related genera, using new field collections, herbarium specimens, and accessioned cultures and sequences. The phylogeny of Mollisiaceae was reconstructed and compared using the nuc internal transcribed spacer rDNA (ITS) barcode and partial sequences of the 28S nuc rDNA (LSU) gene, largest subunit of RNA polymerase II (RPB1), DNA topoisomerase I (TOP1), and the hypothetical protein Lipin/Ned1/Smp2 (LNS2). The results show that endophytism is common throughout the Mollisiaceae lineage in a diverse range of hosts but is infrequently attributed to Mollisia because of a paucity of reference sequences. Generic boundaries within Mollisiaceae are poorly resolved and based on phylogenetic evidence the family included species placed in Acephala, Acidomelania, Barrenia, Bispora, Cheirospora, Cystodendron, Fuscosclera, Hysteronaevia, Loramyces, Mollisia, Neopyrenopeziza, Obtectodiscus, Ombrophila, Patellariopsis, Phialocephala, Pulvinata, Tapesia (=Mollisia), and Trimmatostroma. Taxonomic novelties included the description of five novel Mollisia species and five novel Phialocephala species and the synonymy of Fuscosclera with Phialocephala, Acidomelania with Mollisia, and Loramycetaceae with Mollisiaceae.