Wild trees in the Amazon basin harbor a great diversity of beneficial endosymbiotic fungi: is this evidence of protective mutualism?

Endophyte genomes support greater metabolic gene cluster diversity compared with non-endophytes in Trichoderma

Trichoderma is a cosmopolitan genus with diverse lifestyles and nutritional modes, including mycotrophy, saprophytism, and endophytism. Previous research has reported greater metabolic gene repertoires in endophytic fungal species compared to closely-related non-endophytes. However, the extent of this ecological trend and its underlying mechanisms are unclear. Some endophytic fungi may also be mycotrophs and have one or more mycoparasitism mechanisms. Mycotrophic endophytes are prominent in certain genera like Trichoderma, therefore, the mechanisms that enable these fungi to colonize both living plants and fungi may be the result of expanded metabolic gene repertoires. Our objective was to determine what, if any, genomic features are overrepresented in endophytic fungi genomes in order to undercover the genomic underpinning of the fungal endophytic lifestyle. Here we compared metabolic gene cluster and mycoparasitism gene diversity across a dataset of thirty-eight Trichoderma genomes representing the full breadth of environmental Trichoderma's diverse lifestyles and nutritional modes. We generated four new Trichoderma endophyticum genomes to improve the sampling of endophytic isolates from this genus. As predicted, endophytic Trichoderma genomes contained, on average, more total biosynthetic and degradative gene clusters than non-endophytic isolates, suggesting that the ability to create/modify a diversity of metabolites potential is beneficial or necessary to the endophytic fungi. Still, once the phylogenetic signal was taken in consideration, no particular class of metabolic gene cluster was independently associated with the Trichoderma endophytic lifestyle. Several mycoparasitism genes, but no chitinase genes, were associated with endophytic Trichoderma genomes. Most genomic differences between Trichoderma lifestyles and nutritional modes are difficult to disentangle from phylogenetic divergences among species, suggesting that Trichoderma genomes maybe particularly well-equipped for lifestyle plasticity. We also consider the role of endophytism in diversifying secondary metabolism after identifying the horizontal transfer of the ergot alkaloid gene cluster to Trichoderma.

Two novel endophytic Tolypocladium species identified from native pines in south Florida

This study investigated the incidence and diversity of Tolypocladium within trunks of south Florida slash pines (Pinus densa). Thirty-five isolates were recovered from trunk tissue including living phloem, cambium, and sapwood. Two novel species of Tolypocladium (T. subtropicale and T. trecense) are described here based on morphological and molecular analysis of concatenated LSU, ITS, tef-1, tub, and RPB1 sequences. Our findings expand our understanding of the distribution, diversity, and ecology of this genus and confirm that it is widely spread as an endophyte across ecosystems and hosts. Strains collected in this survey will be used in future bioassays to determine their potential ecological roles as mycoparasites or entomopathogens. Citation: Soares JM, Karlsen-Ayala E, Salvador-Montoya CA, Gazis R (2023). Two novel endophytic Tolypocladium species identified from native pines in south Florida. Fungal Systematics and Evolution 11: 51-61. doi: 10.3114/fuse.2023.11.04.

Genome Resources for the Colletotrichum gloeosporioides Species Complex: 13 Tree Endophytes from the Neotropics and Paleotropics

Thirteen draft genome assemblies are presented for four Colletotrichum gloeosporioides complex species, namely, Colletotrichum aeschynomenes, Colletotrichum asianum, Colletotrichum fructicola, and Colletotrichum siamense, which were isolated from tropical tree hosts as endophytes.

Fungal endophytic community associated with Hevea spp.: diversity, enzymatic activity, and biocontrol potential

Plants of the genus Hevea present a great diversity of endophytic fungal species, which can provide bioactive compounds and enzymes for biotechnological use, and antagonist agents for plant disease biological control. The diversity of endophytic fungi associated with leaves of Hevea spp. clones in western Amazonia was explored using cultivation-based techniques, combined with the sequencing of the ITS rRNA-region. A total of 269 isolates were obtained, and phylogenetic analysis showed that they belong to 47 putative species, of which 24 species were unambiguous. The phylum Ascomycota was the most abundant (95.4%), with predominance of the genera Colletotrichum and Diaporthe, followed by the phylum Basidiomycota (4.6%), with abundance of the genera Trametes and Phanerochaete. Endophytic composition was influenced by the clones, with few species shared among them, and the greatest diversity was found in clone C44 (richness: 26, Shannon: 14,15, Simpson: 9.11). The potential for biocontrol and enzymatic production of endophytes has been investigated. In dual culture tests, 95% of the isolates showed inhibitory activity against C. gloeosporioides, and 84% against C. cassiicola. Efficient inhibition was obtained with isolates HEV158C and HEV255M (Cophinforma atrovirens and Polyporales sp. 2) for C. gloeosporioides, and HEV1A and HEV8B (Phanerochaete sp. 3 and Diaporthe sp. 4) for C. cassiicola. The endophytic isolates were positive for lipase (69.6%), amylase (67.6%), cellulase (33.3%), and protease (20.6%). The enzyme index ≥ 2 was found for amylase and lipase. The isolates obtained from rubber trees showed good antimicrobial and enzymatic potential, which can be tested in the future for use in the industry, and in the control of plant pathogens.

An Integrative View of the Phyllosphere Mycobiome of Native Rubber Trees in the Brazilian Amazon

The rubber tree, Hevea brasiliensis, is a neotropical Amazonian species. Despite its high economic value and fungi associated with native individuals, in its original area in Brazil, it has been scarcely investigated and only using culture-dependent methods. Herein, we integrated in silico approaches with novel field/experimental approaches and a case study of shotgun metagenomics and small RNA metatranscriptomics of an adult individual. Scientific literature, host fungus, and DNA databases are biased to fungal taxa, and are mainly related to rubber tree diseases and in non-native ecosystems. Metabarcoding retrieved specific phyllospheric core fungal communities of all individuals, adults, plantlets, and leaves of the same plant, unravelling hierarchical structured core mycobiomes. Basidiomycotan yeast-like fungi that display the potential to produce antifungal compounds and a complex of non-invasive ectophytic parasites (Sooty Blotch and Flyspeck fungi) co-occurred in all samples, encompassing the strictest core mycobiome. The case study of the same adult tree (previously studied using culture-dependent approach) analyzed by amplicon, shotgun metagenomics, and small RNA transcriptomics revealed a high relative abundance of insect parasite-pathogens, anaerobic fungi and a high expression of Trichoderma (a fungal genus long reported as dominant in healthy wild rubber trees), respectively. Altogether, our study unravels new and intriguing information/hypotheses of the foliar mycobiome of native H. brasiliensis, which may also occur in other native Amazonian trees.

Fungal communities in feces of the frugivorous bat Ectophylla alba and its highly specialized Ficus colubrinae diet

BACKGROUND

Bats are important long-distance dispersers of many tropical plants, yet, by consuming fruits, they may disperse not only the plant's seeds, but also the mycobiota within those fruits. We characterized the culture-dependent and independent fungal communities in fruits of Ficus colubrinae and feces of Ectophylla alba to determine if passage through the digestive tract of bats affected the total mycobiota.

RESULTS

Using presence/absence and normalized abundance data from fruits and feces, we demonstrate that the fungal communities were significantly different, even though there was an overlap of ca. 38% of Amplicon Sequence Variants (ASVs). We show that some of the fungi from fruits were also present and grew from fecal samples. Fecal fungal communities were dominated by Agaricomycetes, followed by Dothideomycetes, Sordariomycetes, Eurotiomycetes, and Malasseziomycetes, while fruit samples were dominated by Dothideomycetes, followed by Sordariomycetes, Agaricomycetes, Eurotiomycetes, and Laboulbeniomycetes. Linear discriminant analyses (LDA) show that, for bat feces, the indicator taxa include Basidiomycota (i.e., Agaricomycetes: Polyporales and Agaricales), and the ascomycetous class Eurotiomycetes (i.e., Eurotiales, Aspergillaceae). For fruits, indicator taxa are in the Ascomycota (i.e., Dothideomycetes: Botryosphaeriales; Laboulbeniomycetes: Pyxidiophorales; and Sordariomycetes: Glomerellales). In our study, the differences in fungal species composition between the two communities (fruits vs. feces) reflected on the changes in the functional diversity. For example, the core community in bat feces is constituted by saprobes and animal commensals, while that of fruits is composed mostly of phytopathogens and arthropod-associated fungi.

CONCLUSIONS

Our study provides the groundwork to continue disentangling the direct and indirect symbiotic relationships in an ecological network that has not received enough attention: fungi-plants-bats. Findings also suggest that the role of frugivores in plant-animal mutualistic networks may extend beyond seed dispersal: they may also promote the dispersal of potentially beneficial microbial symbionts while, for example, hindering those that can cause plant disease.

Influence of plant growth-promoting endophytes Colletotrichum siamense and Diaporthe masirevici on tomato plants (Lycopersicon esculentum Mill.)

The protective and growth-promoting activities of Colletrotrichum and Diaporthe endophytes on tomato plants (Lycopersicon esculentum Mill.) are underexplored. We screened 40 endophytic fungi associated with Mexican shrimp plant (Justicia brandegeana) using an in vitro dual culture assay for Fusarium oxysporum, one of the most important phytopathogens of tomato plants. The three best antagonists, Colletotrichum siamense (JB224.g1), C. siamense (JB252.g1), and Diaporthe masirevicii (JB270), were identified based on multilocus sequence analysis. They were assessed in vitro for their inhibition of F. oxysporum and phosphate solubilisation capacity, and for the production of indole acetic acid. Greenhouse experiments verified the growth-promoting effects of these endophytes and the suppression of F. oxysporum symptoms in tomato plants.   Under greenhouse conditions, the JB252.g1 and JB270 isolates showed positive results for seedling emergence speed. The radicular system depth of plants inoculated with JB270 was greater than that in uninoculated plants (27.21 vs 21.95 cm). The soil plant analysis development chlorophyll metre (SPAD) index showed statistically significant results, especially for the endophyte JB224.g1 (36.99) compared to the control plants (30.90) and plants infected solely with F. oxysporum (33.64).

Synergistic Association With Root Endophytic Fungi Improves Morpho-Physiological and Biochemical Responses of Chenopodium quinoa to Salt Stress

Symbiotic associations with microbes can contribute to mitigating abiotic environmental stress in plants. In this study, we investigated individual and interactive effects of two root endophytic fungal species on physiological and biochemical mechanisms of the crop Chenopodium quinoa in response to salinity. Fungal endophytes (FE) Talaromyces minioluteus and Penicillium murcianum, isolated from quinoa plants that occur naturally in the Atacama Desert, were used for endophyte inoculation. A greenhouse experiment was developed using four plant groups: (1) plants inoculated with T. minioluteus (E1+), (2) plants inoculated with P. murcianum (E2+), (3) plants inoculated with both fungal species (E1E2+), and (4) non-inoculated plants (E-). Plants from each group were then assigned to either salt (300 mM) or control (no salt) treatments. Differences in morphological traits, photosynthesis, stomatal conductance, transpiration, superoxide dismutase (SOD), ascorbate peroxidase (APX), peroxidase, (POD), phenylalanine ammonia-lyase (PAL), phenolic content, and lipid peroxidation between plant groups under each treatment were examined. We found that both endophyte species significantly improved morphological and physiological traits, including plant height, number of shoots, photosynthesis, stomatal conductance, and transpiration, in C. quinoa in response to salt, but optimal physiological responses were observed in E1E2+ plants. Under saline conditions, endophyte inoculation improved SOD, APX, and POD activity by over 50%, and phenolic content by approximately 30%, with optimal enzymatic responses again observed in E1E2+ plants. Lipid peroxidation was significantly lower in inoculated plants than in non-inoculated plants. Results demonstrate that both endophyte species enhanced the ability of C. quinoa to cope with salt stress by improving antioxidative enzyme and non-enzyme systems. In general, both FE species interacting in tandem yielded better morphological, physiological, and biochemical responses to salinity in quinoa than inoculation by a single species in isolation. Our study highlights the importance of stress-adapted FE as a biological agent for mitigating abiotic stress in crop plants.

Lifecycle of Pyrenopeziza protrusa (Helotiales, Dermateaceae sensu lato) in Magnolia obovata revealed by field observation and molecular quantification

Fungi exhibit saprophytic, parasitic, and symbiotic lifestyles, and flexibly switching between them by the environmental changes and host conditions. However, only a few studies have elucidated the detailed changes in fungal DNA or morphology, including the formation of reproductive structures along with lifestyle switching. We hypothesized that Pyrenopeziza protrusa, which occurs abundantly and specifically on Magnolia obovata as a saprophyte, is also associated with living hosts and switches its lifestyles as part of its lifecycle. To elucidate this hypothesis, we periodically sampled the fresh/fallen leaves of M. obovata to observe the seasonal occurrence of reproductive structures for the isolation and detection/quantification of P. protrusa DNA with newly developed species-specific primers. The isolation frequency and amount of P. protrusa DNA drastically increased in the fresh leaves just before defoliation in autumn, but remained high in fallen leaves from autumn to spring. Abundant production of conidiomata and apothecia was also observed in the fallen leaves with increasing DNA content. These results clarified a large part of the lifecycle of P. protrusa, suggesting that the lifestyle is switched from symbiotic to saprophytic stage by significantly increasing the amount of DNA in response to host conditions according to the seasonal variations.

New species and records of Trichoderma isolated as mycoparasites and endophytes from cultivated and wild coffee in Africa

A survey for species of the genus Trichoderma occurring as endophytes of Coffea, and as mycoparasites of coffee rusts (Hemileia), was undertaken in Africa; concentrating on Cameroon and Ethiopia. Ninety-four isolates of Trichoderma were obtained during this study: 76 as endophytes of healthy leaves, stems and berries and, 18 directly from colonized rust pustules. A phylogenetic analysis of all isolates used a combination of three genes: translation elongation factor-1α (tef1), rpb2 and cal for selected isolates. GCPSR criteria were used for the recognition of species; supported by morphological and cultural characters. The results reveal a previously unrecorded diversity of Trichoderma species endophytic in both wild and cultivated Coffea, and mycoparasitic on Hemileia rusts. Sixteen species were delimited, including four novel taxa which are described herein: T. botryosum, T. caeruloviride, T. lentissimum and T. pseudopyramidale. Two of these new species, T. botryosum and T. pseudopyramidale, constituted over 60% of the total isolations, predominantly from wild C. arabica in Ethiopian cloud forest. In sharp contrast, not a single isolate of Trichoderma was obtained using the same isolation protocol during a survey of coffee in four Brazilian states, suggesting the existence of a 'Trichoderma void' in the endophyte mycobiota of coffee outside of Africa. The potential use of these African Trichoderma isolates in classical biological control, either as endophytic bodyguards-to protect coffee plants from Hemileia vastatrix, the fungus causing coffee leaf rust (CLR)-or to reduce its impact through mycoparasitism, is discussed, with reference to the on-going CLR crisis in Central America.

Response of psychrophilic plant endosymbionts to experimental temperature increase

Countless uncertainties remain regarding the effects of global warming on biodiversity, including the ability of organisms to adapt and how that will affect obligate symbiotic relationships. The present study aimed to determine the consequences of temperature increase in the adaptation of plant endosymbionts (endophytes) that grow better at low temperatures (psychrophilic). We isolated fungal endophytes from a high-elevation (paramo) endemic plant, Chusquea subtessellata. Initial growth curves were constructed at different temperatures (4-25°C). Next, experiments were carried out in which only the psychrophilic isolates were subjected to repeated increments in temperature. After the experiments, the final growth curves showed significantly slower growth than the initial curves, and some isolates even ceased to grow. While most studies suggest that the distribution of microorganisms will expand as temperatures increase because most of these organisms grow better at 25°C, the results from our experiments demonstrate that psychrophilic fungi were negatively affected by temperature increases. These outcomes raise questions concerning the potential adaptation of beneficial endosymbiotic fungi in the already threatened high-elevation ecosystems. Assessing the consequences of global warming at all trophic levels is urgent because many species on Earth depend on their microbial symbionts for survival.

Amazonian biogenic volatile organic compounds under global change

Biogenic volatile organic compounds (BVOCs) play important roles at cellular, foliar, ecosystem and atmospheric levels. The Amazonian rainforest represents one of the major global sources of BVOCs, so its study is essential for understanding BVOC dynamics. It also provides insights into the role of such large and biodiverse forest ecosystem in regional and global atmospheric chemistry and climate. We review the current information on Amazonian BVOCs and identify future research priorities exploring biogenic emissions and drivers, ecological interactions, atmospheric impacts, depositional processes and modifications to BVOC dynamics due to changes in climate and land cover. A feedback loop between Amazonian BVOCs and the trends of climate and land-use changes in Amazonia is then constructed. Satellite observations and model simulation time series demonstrate the validity of the proposed loop showing a combined effect of climate change and deforestation on BVOC emission in Amazonia. A decreasing trend of isoprene during the wet season, most likely due to forest biomass loss, and an increasing trend of the sesquiterpene to isoprene ratio during the dry season suggest increasing temperature stress-induced emissions due to climate change.

The diversity and distribution of endophytes across biomes, plant phylogeny and host tissues: how far have we come and where do we go from here?

The interiors of plants are colonized by diverse microorganisms that are referred to as endophytes. Endophytes have received much attention over the past few decades, yet many questions remain unanswered regarding patterns in their biodiversity at local to global scales. To characterize research effort to date, we synthesized results from ~600 published studies. Our survey revealed a global research interest and highlighted several gaps in knowledge. For instance, of the 17 biomes encompassed by our survey, 7 were understudied and together composed only 7% of the studies that we considered. We found that fungal endophyte diversity has been characterized in at least one host from 30% of embryophyte families, while bacterial endophytes have been surveyed in hosts from only 10.5% of families. We complimented our survey with a vote counting procedure to determine endophyte richness patterns among plant tissue types. We found that variation in endophyte assemblages in above-ground tissues varied with host growth habit. Stems were the richest tissue in woody plants, whereas roots were the richest tissue in graminoids. For forbs, we found no consistent differences in relative tissue richness among studies. We propose future directions to fill the gaps in knowledge we uncovered and inspire further research.

Endophytes from Wild Rubber Trees as Antagonists of the Pathogen Corynespora cassiicola

The Corynespora leaf fall disease of rubber trees, caused by the necrotrophic fungus Corynespora cassiicola, is responsible for important yield losses in Asian and African plantations, whereas its impact is negligible in South America. The objective of this study was to identify potential antagonists of C. cassiicola among fungal endophytes (i.e., Pestalotiopsis, Colletotrichum, and Trichoderma spp.) isolated from wild and cultivated rubber trees distributed in the Peruvian Amazon. We first tested the endophytes in dual in vitro confrontation assays against a virulent C. cassiicola isolate (CCP) obtained from diseased rubber trees in the Philippines. All Trichoderma isolates overran the CCP colony, suggesting some antagonistic mechanism, while species from the other genera behaved as mutual antagonists. Trichoderma isolates were then tested through antibiosis assays for their capacity to produce growth-inhibiting molecules. One isolate (LA279), recovered as an endophyte from a wild Hevea guianensis specimen and identified as Trichoderma koningiopsis, showed significant antibiosis capacity. We demonstrated that LA279 was also able to endophytically colonize the cultivated rubber tree species (H. brasiliensis). Under controlled laboratory conditions, rubber plants were inoculated with three Trichoderma strains, including LA279, in combination with the pathogenic CCP. Results showed that 1 week preinoculation with the endophytes differentially reduced CCP mycelial development and symptoms. In conclusion, this study suggests that T. koningiopsis isolate LA279-and derivate compounds-could be a promising candidate for the biological control of the important rubber tree pathogen C. cassiicola.

Exploration of stem endophytic communities revealed developmental stage as one of the drivers of fungal endophytic community assemblages in two Amazonian hardwood genera

Many aspects of the dynamics of tropical fungal endophyte communities are poorly known, including the influence of host taxonomy, host life stage, host defence, and host geographical distance on community assembly and composition. Recent fungal endophyte research has focused on Hevea brasiliensis due to its global importance as the main source of natural rubber. However, almost no data exist on the fungal community harboured within other Hevea species or its sister genus Micrandra. In this study, we expanded sampling to include four additional Hevea spp. and two Micrandra spp., as well as two host developmental stages. Through culture-dependent and -independent (metagenomic) approaches, a total of 381 seedlings and 144 adults distributed across three remote areas within the Peruvian Amazon were sampled. Results from both sampling methodologies indicate that host developmental stage had a greater influence in community assemblage than host taxonomy or locality. Based on FunGuild ecological guild assignments, saprotrophic and mycotrophic endophytes were more frequent in adults, while plant pathogens were dominant in seedlings. Trichoderma was the most abundant genus recovered from adult trees while Diaporthe prevailed in seedlings. Potential explanations for that disparity of abundance are discussed in relation to plant physiological traits and community ecology hypotheses.

Forest Tree Microbiomes and Associated Fungal Endophytes: Functional Roles and Impact on Forest Health

Terrestrial plants including forest trees are generally known to live in close association with microbial organisms. The inherent features of this close association can be commensalism, parasitism or mutualism. The term “microbiota” has been used to describe this ecological community of plant-associated pathogenic, mutualistic, endophytic and commensal microorganisms. Many of these microbiota inhabiting forest trees could have a potential impact on the health of, and disease progression in, forest biomes. Comparatively, studies on forest tree microbiomes and their roles in mutualism and disease lag far behind parallel work on crop and human microbiome projects. Very recently, our understanding of plant and tree microbiomes has been enriched due to novel technological advances using metabarcoding, metagenomics, metatranscriptomics and metaproteomics approaches. In addition, the availability of massive DNA databases (e.g., NCBI (USA), EMBL (Europe), DDBJ (Japan), UNITE (Estonia)) as well as powerful computational and bioinformatics tools has helped to facilitate data mining by researchers across diverse disciplines. Available data demonstrate that plant phyllosphere bacterial communities are dominated by members of only a few phyla (Proteobacteria, Actinobacteria, Bacteroidetes). In bulk forest soil, the dominant fungal group is Basidiomycota, whereas Ascomycota is the most prevalent group within plant tissues. The current challenge, however, is how to harness and link the acquired knowledge on microbiomes for translational forest management. Among tree-associated microorganisms, endophytic fungal biota are attracting a lot of attention for their beneficial health- and growth-promoting effects, and were preferentially discussed in this review.

A multiscale study of fungal endophyte communities of the foliar endosphere of native rubber trees in Eastern Amazon

Hevea brasiliensis is a native hyperdiverse tree species in the Amazon basin with great economic importance since it produces the highest quality natural rubber. H. brasiliensis, in its natural habitat, may harbor fungal endophytes that help defend against phytopathogenic fungi. In this work, we investigated the fungal endophytic communities in two pristine areas in Eastern Amazon (Anavilhanas National Park - ANP and Caxiuanã National Forest - CNF) at different spatial scales: regional, local, individual (tree), and intra-individual (leaflet). Using a culture-based approach, 210 fungal endophytes were isolated from 240 sampling units and assigned to 46 distinct MOTUs based on sequencing of the nrITS DNA. The community compositions of the endophytomes are different at both regional and local scales, dominated by very few taxa and highly skewed toward rare taxa, with many endophytes infrequently isolated across hosts in sampled space. Colletotrichum sp. 1, a probably latent pathogen, was the most abundant endophytic putative species and was obtained from all individual host trees in both study areas. Although the second most abundant putative species differed between the two collection sites, Clonostachys sp. 1 and Trichoderma sp. 1, they are phylogenetically related (Hypocreales) mycoparasites. Thus, they probably exhibit the same ecological function in the foliar endosphere of rubber tree as antagonists of its fungal pathogens.

Habitat conditions and phenological tree traits overrule the influence of tree genotype in the needle mycobiome-Picea glauca system at an arctic treeline ecotone

Plant-associated mycobiomes in extreme habitats are understudied and poorly understood. We analysed Illumina-generated ITS1 sequences from the needle mycobiome of white spruce (Picea glauca) at the northern treeline in Alaska (USA). Sequences were obtained from the same DNA that was used for tree genotyping. In the present study, fungal metabarcoding and tree microsatellite data were compared for the first time. In general, neighbouring trees shared more fungal taxa with each other than trees growing in further distance. Mycobiomes correlated strongly with phenological host traits and local habitat characteristics contrasting a dense forest stand with an open treeline site. Genetic similarity between trees did not influence fungal composition and no significant correlation existed between needle mycobiome and tree genotype. Our results suggest the pronounced influence of local habitat conditions and phenotypic tree traits on needle-inhabiting fungi. By contrast, the tree genetic identity cannot be benchmarked as a dominant driver for needle-inhabiting mycobiomes, at least not for white spruce in this extreme environment.

The defensive role of foliar endophytic fungi for a South American tree

Fungal endophytes colonize living internal plant tissues without causing any visible symptoms of disease. Endophytic fungi associated with healthy leaves may play an important role in the protection of hosts against herbivores and pathogens. In this study, the diversity of foliar endophytic fungi (FEF) of the southern temperate tree Embothrium coccineum (Proteaceae), as well as their role in plant protection in nature was determined. Fungal endophytes were isolated from 40 asymptomatic leaves by the culture method for molecular identification of the 18S rRNA gene. A relationship between FEF frequency and plant protection was evaluated in juveniles of E. coccineum Fungal endophyte frequency was estimated using real-time PCR analyses to determine endophyte DNA content per plant. A total of 178 fungal isolates were identified, with sequence data revealing 34 different operational taxonomic units (OTUs). A few common taxa dominated the fungal endophyte community, whereas most taxa qualified as rare. A significant positive correlation between plant protection (evaluated in terms of percentage of leaf damage) and FEF frequency was found. Furthermore, in vitro confrontation assays indicated that FEF were able to inhibit the growth of fungal pathogens. The data showed a relatively high diversity of fungal endophytes associated with leaves of E. coccineum, and suggest a positive relationship between fungal endophyte frequencies in leaves and host protection in nature.

Endophytic Fungi from Frankincense Tree Improves Host Growth and Produces Extracellular Enzymes and Indole Acetic Acid

Boswellia sacra, an economically important frankincense-producing tree found in the desert woodlands of Oman, is least known for its endophytic fungal diversity and the potential of these fungi to produce extracellular enzymes and auxins. We isolated various fungal endophytes belonging to Eurotiales (11.8%), Chaetomiaceae (17.6%), Incertae sadis (29.5%), Aureobasidiaceae (17.6%), Nectriaceae (5.9%) and Sporomiaceae (17.6%) from the phylloplane (leaf) and caulosphere (stem) of the tree. Endophytes were identified using genomic DNA extraction, PCR amplification and sequencing the internal transcribed spacer regions, whereas a detailed phylogenetic analysis of the same gene fragment was made with homologous sequences. The endophytic colonization rate was significantly higher in the leaf (5.33%) than the stem (0.262%). The Shannon-Weiner diversity index was H′ 0.8729, while Simpson index was higher in the leaf (0.583) than in the stem (0.416). Regarding the endophytic fungi’s potential for extracellular enzyme production, fluorogenic 4-methylumbelliferone standards and substrates were used to determine the presence of cellulases, phosphatases and glucosidases in the pure culture. Among fungal strains, Penicillum citrinum BSL17 showed significantly higher amounts of glucosidases (62.15±1.8 μM^-1min^-1mL) and cellulases (62.11±1.6 μM^-1min^-1mL), whereas Preussia sp. BSL10 showed significantly higher secretion of glucosidases (69.4±0.79 μM^-1min^-1mL) and phosphatases (3.46±0.31μM^-1min^-1mL) compared to other strains. Aureobasidium sp. BSS6 and Preussia sp. BSL10 showed significantly higher potential for indole acetic acid production (tryptophan-dependent and independent pathways). Preussia sp. BSL10 was applied to the host B. sacra tree saplings, which exhibited significant improvements in plant growth parameters and accumulation of photosynthetic pigments. The current study concluded that endophytic microbial resources producing extracellular enzymes and auxin could establish a unique niche for ecological adaptation during symbiosis with the host Frankincense tree.