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Pine Seeds Carry Symbionts: Endophyte Transmission Re-examined
Abstract
Observations resulting from an increased scrutiny of seed-borne microbes are challenging our traditional concepts of endophyte transmission, but few of these studies have focused on trees, particularly the conifers that dominate many forested ecosystems. We reviewed the literature on pine seed endophytes and examined two pine species, pinyon (Pinus edulis) and ponderosa (P. ponderosa), in northern Arizona by culture-based and/or culture-independent methods. We predicted that the long seed development period in pines would be conducive to the assembly of a diverse seed microbiome. In the culture-based studies, the following patterns emerged: (1) pinyon pine had higher numbers of microbes isolated from its seeds than ponderosa pine. (2) One pinyon phenotype that is herbivore susceptible but drought tolerant (H−D+) had more culturable microbes associated with its seeds than the herbivore-resistant/drought-intolerant phenotype (H+D−). (3) H−D+ bacteria were of a different phylum (Gammaproteobacteria) than H+D− pinyon bacteria and ponderosa pine (Firmicutes). In our culture-independent study, fungal DNA sequences obtained from ponderosa seed were primarily basidiomycete fungi, many of which were ectomycorrhizal species. We infer that the presence of symbiotic fungal taxa and the relative absence of common environmental fungi in two species of pine seed imply filtering of the seed microbiome. We discuss endophyte transmission and propose a new mode, reticulate transmission, which combines elements of both vertical and horizontal transmission.
... Considering microbial diversity in ecosystem restoration is therefore of critical importance. However, there is a distinct lack of baseline microbiome information for natural ecosystems, with most of our knowledge originating from surveys of agricultural plants (Clay 1987;Clay and Holah 1999;Arnold and Herre 2003;Afkhami and Rudgers 2008;Compant et al. 2011;Barret et al. 2015;Giauque and Hawkes 2016;Klaedtke et al. 2016;Adam et al. 2018), forestry species (Helander et al. 1994;Deckert et al. 2019;Bergmann and Busby 2021) and soil microbiomes (Peay et al. 2007;Heneghan et al. 2008;Mu ñoz-Rojas et al. 2016;Gellie et al. 2017;Schöler et al. 2017;Leff et al. 2018;Saleem et al. 2019;Ngugi et al. 2020). ...
Context: Seeds harbour a diversity of microbes, which in some plants aid with germination and establishment. Seeds form a critical part in the lifecycle of plants and a role in many conservation and restoration activities. Aims: Because this is an emerging field in seed biology, we aim to highlight the key research gaps of interest to seed on the basis of restoration and ex situ conservation. Methods: We identify knowledge gaps associated with the seed endophytic microbiome of native Australian plants through undertaking a literature review. Additionally, culturing methods were used to identify the fungal seed endophytes of five native Australian species. Key results: We identified a diversity of taxa within the native seed and show three taxa that are common to all study hosts. Sampling seed from additional hosts at a site and additional sites of a host species showed new fungal diversity. Our literature review showed that little information is available on native seed microbiomes and we identified four key areas where research gaps exist, linking with seed-based restoration practices. Conclusions: We provide evidence that there is a complex and diverse seed microbiome within some Australian native plants and suggest ways that it could be integrated into restoration and conservation practices. Implications: We propose that by taking into consideration the presence of a seed microbiome and its potential impacts on plant health, seed microbiomes could be used as one method to restore microbial diversity into an ecosystem and to contribute to the seedling microbiome and plant health at restored sites. © 2023 The Author(s) (or their employer(s)). Published by CSIRO Publishing.
... Rhizosphaera kalkhoffii has been detected in the twigs of A. beshanzuensis (Yuan et al., 2011) and P. abies (Sieber, 1989). Remarkably, R. kalkhoffii is usually isolated in needles and seeds (Deckert et al., 2019;Magan and Smith, 1996;Sieber, 1988). R. kalkhoffii can also be pathogenic for the hosts when it occurs as a needle cast pathogen (Diamandis and Minter, 1980;Scattolin and Montecchio, 2009). ...
... The microbial contributions of the vertical and floral transmission pathways are likely to vary based on a plant species' pollination mode (Chesneau et al., 2020). Horizontal transmission is the acquisition of seed microbes from the environment, either prior to or after the maturation of the seed as it is still attached to the mother plant (Deckert et al., 2019) or as Variation in plant microbial communities can be observed at the macro-scale (i.e., meters to kilometers, or within and among sampling sites), meso-scale (i.e., centimeters to meters, or within and among plant organs to individuals), and micro-scale (i.e., nanometers to centimeters, or within and among plant organs) scales. The different colored stars represented distinct microbial communities at each scale. ...
Microorganisms have the potential to affect plant seed germination and seedling fitness, ultimately impacting plant health and community dynamics. Because seed-associated microbiota are highly variable across individual plants, plant species, and environments, it is challenging to identify the dominant processes that underlie the assembly, composition, and influence of these communities. We propose here that metacommunity ecology provides a conceptually useful framework for studying the microbiota of developing seeds, by the application of metacommunity principles of filtering, species interactions, and dispersal at multiple scales. Many studies in seed microbial ecology already describe individual assembly processes in a pattern-based manner, such as correlating seed microbiome composition with genotype or tracking diversity metrics across treatments in dispersal limitation experiments. But we see a lot of opportunities to examine understudied aspects of seed microbiology, including trait-based research on mechanisms of filtering and dispersal at the micro-scale, the use of pollination exclusion experiments in macro-scale seed studies, and an in-depth evaluation of how these processes interact via priority effect experiments and joint species distribution modeling.
... Rhizosphaera kalkhoffii has been detected in the twigs of A. beshanzuensis (Yuan et al., 2011) and P. abies (Sieber, 1989). Remarkably, R. kalkhoffii is usually isolated in needles and seeds (Deckert et al., 2019;Magan and Smith, 1996;Sieber, 1988). R. kalkhoffii can also be pathogenic for the hosts when it occurs as a needle cast pathogen (Diamandis and Minter, 1980;Scattolin and Montecchio, 2009). ...
In this chapter, we review the research on fungi present in the woody tissues of trees. The functions of fungi in stems are variable and can be mutualistic, commensalistic, saprotrophic, or pathogenic. We cover endophytic fungi found in the nonfoliage parts of woody tissues of conifers and broadleaf trees. The lifestyle switches of endophytes and the pathogenic fungi of stems and branches are discussed. Fungi have an important role in tree health and the nutrient cycle, especially wood decay. Similarly, there is evidence that changes in local environments can benefit opportunistic pathogens to switch their lifestyle from endophytic. The identity of species compositions of endophytes of healthy and diseased trees is extremely important to maintain forest resilience in a changing world.
... Entry into the root tissues occurs by root cracks or lateral roots emergence points as well as during water/nutrient absorption . The next step in the series of events to colonization is endophytes transmission within plants (Gibert et al., 2015;Frank et al., 2017;Deckert et al., 2019). It is directly influenced by the colonizing ability and allocation of food resources to different organs. ...
In the past few decades course, the global human population has grown tremendously and reached 7.712 billion counts by 2019. It is expected to cross the whopping mark of 10 billion by 2053. This every second escalating growth has also directly increased the application of human-made fertilizers, the intensity of agricultural practices, and much wider use of chemicals like weedicides, insecticides, and multiple diseases controlling agents. However, along with other anthropogenic activities, the situation has somewhere worsened. As a result, the primary focus of the current age researchers is to increase the overall output yield of every crop as well as maintaining or enhancing soil fertility in an eco-friendly manner. Currently, various groups of researchers are working throughout the globe via different approaches. One of the prominent options that emerged during the last decade is microbiome engineering. It includes the engineering of every component of epiphytic, endophytic, and rhizospheric microbiome. It creates a unique set of conditions to enhance the interaction between plants and their associated microbes. However, the prerequisite for microbial engineering is the ample amount of knowledge of the plant’s microbiome. One of the prominent global crops in which the microbiome studies have been conducted in maize (Zea mays L., family Poaceae). Therefore, in the current book chapter, we have critically reviewed the relevant literature regarding the maize microbiome chiefly from the last decade. Additionally, the isolation method of maize microbiome and microbiome targeted maize breeding has been discussed.
Endophytic microbial communities of crop plants interact intimately with hosts and are associated with almost every plant. Endophytic microorganisms exhibit an array of plant beneficial traits similar to those reported for plant growth–promoting rhizobacteria (PGPR). Their localization inside the plant gives them an advantage over rhizobacteria in terms of availability of nutrients and shield against external unfavorable conditions. However, many microbial and host traits as well as environmental factors influence endophytic colonization. In the last decade, several reports have been published on the isolation of endophytic microorganisms from different plant tissues and their role in promoting plant growth under various environmental conditions. Seed endophytes are of great interest because of their capability to colonize the developing seeds, stay latent in the dormant seed, and transmit to the next generation after germination and plant development. Endophytic bacteria isolated from seeds have been found to produce antimicrobial compounds, phytohormones, enzymes, secondary metabolites, etc. that make them industrially as well as agriculturally very important. Application of seed endophytes has been reported to improve plant growth and physiological status under biotic and abiotic stress conditions. Limited studies have also reported their influence on plant gene expression resulting in altered physiological response. However, focused research is needed to study the vast diversity of endophytes in different crops and also to unravel their interaction with host plants, for their potential application in agriculture. The present book chapter aims to focus on the significance of seed endophytes, their entry, establishment, diversity, and interactions with host plants along with the applications in agriculture under changing climatic conditions. A better understanding of plant-endophyte interaction can help in the optimization of plant microbiome and microbe assisted breeding in the near future.
The interactions among climate change, plant genetic variation and fungal mutualists are poorly understood, but probably important to plant survival under drought. We examined these interactions by studying the ectomycorrhizal fungal ( EMF ) communities of pinyon pine seedlings ( Pinus edulis ) planted in a wildland ecosystem experiencing two decades of climate change‐related drought.
We established a common garden containing P. edulis seedlings of known maternal lineages (drought tolerant, DT ; drought intolerant, DI ), manipulated soil moisture and measured EMF community structure and seedling growth.
Three findings emerged: EMF community composition differed at the phylum level between DT and DI seedlings, and diversity was two‐fold greater in DT than in DI seedlings. EMF communities of DT seedlings did not shift with water treatment and were dominated by an ascomycete, Geopora sp. By contrast, DI seedlings shifted to basidiomycete dominance with increased moisture, demonstrating a lineage by environment interaction. DT seedlings grew larger than DI seedlings in high (28%) and low (50%) watering treatments.
These results show that inherited plant traits strongly influence microbial communities, interacting with drought to affect seedling performance. These interactions and their potential feedback effects may influence the success of trees, such as P. edulis , in future climates.
Phytobeneficial microbes, particularly endophytes, such as fungi and bacteria, are concomitant partners of plants throughout its developmental stages, including seed germination, root and stem growth, and fruiting. Endophytic microbes have been identified in plants that grow in a wide array of habitats; however, seed-borne endophytic microbes have not been fully explored yet. Seed-borne endophytes are of great interest because of their vertical transmission; their potential to produce various phytohormones, enzymes, antimicrobial compounds, and other secondary metabolites; and improve plant biomass and yield under biotic and abiotic stresses. This review addresses the current knowledge on endophytes, their ability to produce metabolites, and their influence on plant growth and stress mitigation.
Plants are hosts to complex communities of endophytic bacteria that colonize the interior of both below- and aboveground tissues. Bacteria living inside plant tissues as endophytes can be horizontally acquired from the environment with each new generation, or vertically transmitted from generation to generation via seed. A better understanding of bacterial endophyte transmission routes and modes will benefit studies of plant–endophyte interactions in both agricultural and natural ecosystems. In this review, we provide an overview of the transmission routes that bacteria can take to colonize plants, including vertically via seeds and pollen, and horizontally via soil, atmosphere, and insects. We discuss both well-documented and understudied transmission routes, and identify gaps in our knowledge on how bacteria reach the inside of plants. Where little knowledge is available on endophytes, we draw from studies on bacterial plant pathogens to discuss potential transmission routes. Colonization of roots from soil is the best studied transmission route, and probably the most important, although more studies of transmission to aerial parts and stomatal colonization are needed, as are studies that conclusively confirm vertical transfer. While vertical transfer of bacterial endophytes likely occurs, obligate and strictly vertically transferred symbioses with bacteria are probably unusual in plants. Instead, plants appear to benefit from the ability to respond to a changing environment by acquiring its endophytic microbiome anew with each generation, and over the lifetime of individuals.
Forest and woodland ecosystems play a crucial role in the global carbon cycle and may be strongly affected by changing climate. Here, we use an individual-based approach to model piñon pine (Pinus edulis) radial growth responses to climate across gradients of environmental stress. We sampled piñon pine trees at 24 sites across southwestern Colorado that varied in soil available water capacity (AWC), elevation, and latitude, obtaining a total of 552 piñon pine tree ring series. We used linear mixed-effect models to assess piñon pine growth responses to climate and site-level environmental stress (30-year mean cumulative climatic water deficit [CWD] and soil AWC). Using a similar modeling approach, we also determined long-term growth trends across our gradients of environmental stress. Piñon pine growth was strongly positively associated with winter precipitation. Summer vapor pressure deficit (VPD) was strongly negatively associated with piñon pine growth during years of low winter precipitation, whereas summer VPD had no effect on piñon pine growth during years of high winter precipitation. The strength of the relationship between the annual climatic variables (winter precipitation and summer VPD) and piñon pine growth was also influenced by site-level environmental stress, suggesting that the sensitivity of woodland ecosystems to changing climate will vary across the landscape due to differences in local physiographic conditions. Trees at sites with lower CWDs were more responsive to summer VPD, showing greater reductions in growth rates during warmer years. Trees at sites with greater soil AWC were more responsive to winter precipitation, showing higher growth rates during years of high precipitation. Piñon pine growth rates declined moderately over the past century across our study area, suggesting that recent increases in aridity have resulted in long-term growth declines.
The microbial component of healthy seeds – the seed microbiome – appears to be inherited between plant generations and can dynamically influence germination, plant performance, and survival. As such, methods to optimize the seed microbiomes of major crops could have far-reaching implications for plant breeding and crop improvement to enhance agricultural food, feed, and fiber production. Here, we describe a new approach to modulate seed microbiomes of elite crop seed embryos and concomitantly design the traits to be mediated by seed microbiomes. Specifically, we discovered that by introducing the endophyte Paraburkholderia phytofirmans PsJN to the flowers of parent plants we could drive its inclusion in progeny seed microbiomes, thereby inducing vertical inheritance to the offspring generation. We demonstrated the introduction of PsJN to seeds of monocot and dicot plant species and the consequential modifications to seed microbiome composition and growth traits in wheat, illustrating the potential role of novel seed-based microbiomes in determining plant traits.
With high-throughput sequencing (HTS), we are able to explore the hidden world of microscopic organisms to an unpre-cedented level. The fast development of molecular technology and statistical methods means that microbial ecologists must keep their toolkits updated. Here, we review and evaluate some of the more widely adopted and emerging techniques for analysis of diversity and community composition, and the inference of species interactions from co-occurrence data generated by HTS of marker genes. We emphasize the importance of observational biases and statistical properties of the data and methods. The aim of the review is to critically discuss the advantages and disadvantages of established and emerging statistical methods, and to contribute to the integration of HTS-based marker gene data into community ecology.
The Sebacinales are a monophyletic group of ubiquitous hymenomycetous mycobionts which form ericoid and orchid mycorrhizae, ecto- and ectendomycorrhizae, and nonspecific root endophytic associations with a wide spectrum of plants. However, due to the complete lack of fungal isolates derived from Ericaceae roots, the Sebacinales ericoid mycorrhizal (ErM) potential has not yet been tested experimentally. Here, we report for the first time isolation of a serendipitoid (formerly Sebacinales Group B) mycobiont from Ericaceae which survived in pure culture for several years. This allowed us to test its ability to form ericoid mycorrhizae with an Ericaceae host in vitro, to describe its development and colonization pattern in host roots over time, and to compare its performance with typical ErM fungi and other serendipitoids derived from non-Ericaceae hosts. Out of ten serendipitoid isolates tested, eight intracellularly colonized Vaccinium hair roots, but only the Ericaceae-derived isolate repeatedly formed typical ericoid mycorrhiza morphologically identical to ericoid mycorrhiza commonly found in naturally colonized Ericaceae, but yet different from ericoid mycorrhiza formed in vitro by the prominent ascomycetous ErM fungus Rhizoscyphus ericae. One Orchidaceae-derived isolate repeatedly formed abundant hyaline intracellular microsclerotia morphologically identical to those occasionally found in naturally colonized Ericaceae, and an isolate of Serendipita (= Piriformospora) indica produced abundant intracellular chlamydospores typical of this species. Our results confirm for the first time experimentally that some Sebacinales can form ericoid mycorrhiza, point to their broad endophytic potential in Ericaceae hosts, and suggest possible ericoid mycorrhizal specificity in Serendipitaceae.
Seed dispersal mutualisms with scatter-hoarders play a crucial role in population dynamics of temperate large-seeded trees. These behaviors shape seed dispersal patterns, which can be applied to conservation of populations, communities, and even ecosystems dominated by large-seeded trees. We draw on a growing body of literature to describe the ecological context and consequences of scatter-hoarding as a seed dispersal mechanism. We synthesize the quantitative literature on the interaction between members of the avian family Corvidae (crows, ravens, jays, magpies, and nutcrackers) and nut-bearing trees such as pines (Pinus spp.) and oaks (Quercus spp.) to examine unique aspects of avian scatter-hoarders as seed dispersers. During the scatter-hoarding process, seed selectivity, transportation distance, hoarding frequency, and cache placement affect seed dispersal effectiveness, a measure of the quantity and quality of dispersal. Case studies from around the world highlight the role of corvid seed dispersal in population dynamics of trees, and how the birds' scatter-hoarding behavior can be facilitated for the restoration of oak- and pine-dominated habitats. This mutualism, which provides many plant species with long-distance, high-quality seed dispersal, will likely become even more important for conservation of oak and pine ecosystems as suitable climates shift rapidly in the decades ahead. This ecosystem service provided by corvids could therefore serve as an efficient conservation tool.
Many fungi belonging to mostly Ascomycota inhabit living tissues of plants of all major lineages without causing any visible symptoms. Termed horizontally transmitted endophytes, they have been investigated mostly for their capacity to produce bioactive secondary metabolites. However, many questions regarding the interactions between endophytes and their plant hosts, phytophagous insects and other fungi remain unanswered. This review highlights some of these areas of endophyte biology about which very little or no knowledge exists. Information garnered' using modern methodologies' on these grey areas of ‘endophytism’ (endophytic mode of lifestyle) would help immensely in understanding the evolution of endophytes of aerial plant tissues and in exploiting endophytes in various fields of biotechnology.
All plants are inhabited internally by diverse microbial communities comprising bacterial, archaeal, fungal, and protistic taxa. These microorganisms showing endophytic lifestyles play crucial roles in plant development, growth, fitness, and diversification. The increasing awareness of and information on endophytes provide insight into the complexity of the plant microbiome. The nature of plant-endophyte interactions ranges from mutualism to pathogenicity. This depends on a set of abiotic and biotic factors, including the genotypes of plants and microbes, environmental conditions, and the dynamic network of interactions within the plant biome. In this review, we address the concept of endophytism, considering the latest insights into evolution, plant ecosystem functioning, and multipartite interactions.
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Unlabelled:
Endophytes are microbes that inhabit plant tissues without any apparent signs of infection, often fundamentally altering plant phenotypes. While endophytes are typically studied in plant roots, where they colonize the apoplast or dead cells, Methylobacterium extorquens strain DSM13060 is a facultatively intracellular symbiont of the meristematic cells of Scots pine (Pinus sylvestris L.) shoot tips. The bacterium promotes host growth and development without the production of known plant growth-stimulating factors. Our objective was to examine intracellular colonization by M. extorquens DSM13060 of Scots pine and sequence its genome to identify novel molecular mechanisms potentially involved in intracellular colonization and plant growth promotion. Reporter construct analysis of known growth promotion genes demonstrated that these were only weakly active inside the plant or not expressed at all. We found that bacterial cells accumulate near the nucleus in intact, living pine cells, pointing to host nuclear processes as the target of the symbiont's activity. Genome analysis identified a set of eukaryote-like functions that are common as effectors in intracellular bacterial pathogens, supporting the notion of intracellular bacterial activity. These include ankyrin repeats, transcription factors, and host-defense silencing functions and may be secreted by a recently imported type IV secretion system. Potential factors involved in host growth include three copies of phospholipase A2, an enzyme that is rare in bacteria but implicated in a range of plant cellular processes, and proteins putatively involved in gibberellin biosynthesis. Our results describe a novel endophytic niche and create a foundation for postgenomic studies of a symbiosis with potential applications in forestry and agriculture.
Importance:
All multicellular eukaryotes host communities of essential microbes, but most of these interactions are still poorly understood. In plants, bacterial endophytes are found inside all tissues. M. extorquens DSM13060 occupies an unusual niche inside cells of the dividing shoot tissues of a pine and stimulates seedling growth without producing cytokinin, auxin, or other plant hormones commonly synthesized by plant-associated bacteria. Here, we tracked the bacteria using a fluorescent tag and confocal laser scanning microscopy and found that they localize near the nucleus of the plant cell. This prompted us to sequence the genome and identify proteins that may affect host growth by targeting processes in the host cytoplasm and nucleus. We found many novel genes whose products may modulate plant processes from within the plant cell. Our results open up new avenues to better understand how bacteria assist in plant growth, with broad implications for plant science, forestry, and agriculture.
Many grasses are infected by systemic fungal endophytes (Clavicipitaceae, Ascomycetes) that produce physiologically active alkaloids in the tissues of their hosts. Infection makes grasses toxic to domestic mammals and increases resistance to insect herbivores. Some grasses are sterilized by endophyte infection while remaining vegetatively vigorous; other infected grasses remain completely fertile. Plant growth and seed production can be increased by infection. This symbiotic association may be a defensive mutualism in which the fungi defend their hosts against herbivory, thereby defending their own resources. -from Author
To date, it has been thought that endophytic fungi in forbs infect the leaves of their hosts most commonly by air-borne spores (termed "horizontal transmission"). Here, we show that vertical transmission from mother plant to offspring, via seeds, occurs in six forb species (Centaurea cyanus, C. nigra,Papaver rhoeas,Plantago lanceolata,Rumex acetosa, and Senecio vulgaris), suggesting that this may be a widespread phenomenon. Mature seeds were collected from field-grown plants and endophytes isolated from these, and from subsequent cotyledons and true leaves of seedlings, grown in sterile conditions. Most seeds contain one species of fungus, although the identity of the endophyte differs between plant species. Strong evidence for vertical transmission was found for two endophyte species, Alternaria alternata and Cladosporium sphaerospermum. These fungi were recovered from within seeds, cotyledons, and true leaves, although the plant species they were associated with differed. Vertical transmission appears to be an imperfect process, and germination seems to present a bottleneck for fungal growth. We also found that A. alternata and C. sphaerospermum occur on, and within pollen grains, showing that endophyte transmission can be both within and between plant generations. Fungal growth with the pollen tube is likely to be the way in which endophytes enter the developing seed. The fact that true vertical transmission seems common suggests a more mutualistic association between these fungi and their hosts than has previously been thought, and possession of endophytes by seedling plants could have far-reaching ecological consequences. Seedlings may have different growth rates and be better protected against herbivores and pathogens, dependent on the fungi that were present in the mother plant. This would represent a novel case of trans-generational resistance in plants.
In order to address the hypothesis that seeds from ecologically and geographically diverse plants harbor characteristic epiphytic microbiota, we characterized the bacterial and fungal microbiota associated with Triticum and Brassica seed surfaces.
The total microbial complement was determined by amplification and sequencing of a fragment of chaperonin 60 (cpn60). Specific microorganisms were quantified by qPCR. Bacteria and fungi corresponding to operational taxonomic units (OTU) that were identified in the sequencing study were isolated and their interactions examined.
A total of 5477 OTU were observed from seed washes. Neither total epiphytic bacterial load nor community richness/evenness was significantly different between the seed types; 578 OTU were shared among all samples at a variety of abundances. Hierarchical clustering revealed that 203 were significantly different in abundance on Triticum seeds compared with Brassica. Microorganisms isolated from seeds showed 99–100% identity between the cpn60 sequences of the isolates and the OTU sequences from this shared microbiome. Bacterial strains identified as Pantoea agglomerans had antagonistic properties toward one of the fungal isolates (Alternaria sp.), providing a possible explanation for their reciprocal abundances on both Triticum and Brassica seeds.
cpn60 enabled the simultaneous profiling of bacterial and fungal microbiota and revealed a core seed-associated microbiota shared between diverse plant genera.
Models analyzing how Southwestern plant communities will respond to climate change predict that increases in temperature will lead to upward elevational shifts of montane species. We tested this hypothesis by reexamining Robert Whittaker's 1963 plant transect in the Santa Catalina Mountains of southern Arizona, finding that this process is already well underway. Our survey, five decades after Whittaker's, reveals large changes in the elevational ranges of common montane plants, while mean annual rainfall has decreased over the past 20 years, and mean annual temperatures increased 0.25°C/decade from 1949 to 2011 in the Tucson Basin. Although elevational changes in species are individualistic, significant overall upward movement of the lower elevation boundaries, and elevational range contractions, have occurred. This is the first documentation of significant upward shifts of lower elevation range boundaries in Southwestern montane plant species over decadal time, confirming that previous hypotheses are correct in their prediction that mountain communities in the Southwest will be strongly impacted by warming, and that the Southwest is already experiencing a rapid vegetation change.
Culturing needles at early stages of discolouration and a number of experiments failed to show that R. kalkhoffii or any other fungus has a primary involvement in foliar symptoms in “top-dying” of Norway spruce by attacking the needles or shoots of the last two years'growth.
Fungicides failed to arrest the disease. Needle browning was temporarily prevented by bagging shoots of diseased trees at the start of the flushing period. R. kalkhoffii could colonize pulvini as well as
▪ Abstract Endophytic fungi living asymptomatically within plant tissues have been found in virtually all plant species. Endophytes are considered plant mutualists: They receive nutrition and protection from the host plant while the host plant may benefit from enhanced competitive abilities and increased resistance to herbivores, pathogens, and various abiotic stresses. Limited evidence also indicates that endophytes may influence population dynamics, plant community diversity, and ecosystem function. However, most of the empirical evidence for this mutualism and its ecological consequences has been based on a few agronomic grass endophytes. More recent studies suggest that endophyte-host plant interactions are variable and range from antagonistic to mutualistic. A more comprehensive view of the ecology and evolution of endophytes and host plants is needed. This article discusses how life history traits—such as fungal reproduction and pattern of infections and genotypic variation and ecological factors—in...
Optical microscopy of recently living and cleared material of the fucoid, Ascophyllum nodosum (L.) Le Jolis, revealed novel aspects of its interaction with the ascomycete Mycophycias ascophylli (Cotton) Kohlmeyer and Kohlmeyer (previously Mycosphaerella ascophylli Cotton). Most host cells are associated with hyphae by lateral attachment of cell walls. Hyphae form extensive networks throughout the host thallus and show considerable differentiation in the various host tissues. In the base of epidermal cells, hyphae form multicellular rings around each host cell to produce a continuous network. In medullary regions, long, relatively unbranched and longitudinally aligned hyphae occur, with radial branches extending into cortical regions. Scattered in the inner cortex of host tissue are numerous multicellular nodes of smaller, polygonal to irregular shaped cells with five or more radiating arms of hyphae. Individual hyphal cells show a variety of specializations including swellings and appressoria-like attachments to some host cells. These observations provide the morphological basis for the mutualistic symbiosis supported by recent experimental work. We conclude that this association is best described by the term “symbiotum.”
Within- and among-tree variation in assemblages of endophytic fungi in Scots pine (Pinus sylvestris) needles were studied in a subarctic area where background pollution values are low; the effects of tree density and prolonged simulated acid rain on the occurrence of endophytic fungi were investigated. The needle endophyte most frequently isolated was Cenangium ferruginosum, accounting for 64% of all fungal individuals, followed by Cyclaneusma minus (12% of all individuals). Old needles were colonized more frequently by endophytes than young ones. In young needles the colonization by endophytes increased during the summer, whereas in old ones no seasonal variation was detected. Endophyte colonization was positively correlated with stand density and was reduced on pines treated with spring water acidified with either sulphuric acid alone or in combination with nitric acid. In contrast, nitric acid alone did not affect endophyte colonization. Key words: endophytes, needles, pine, Pinus, simulated acid rain,...
Significance
Soil microbes influence plant performance and may be critical to the persistence of some plants with climate change. However, microbes are highly diverse, and individuals of the same plant species often associate with different microbes. We examined the importance of soil microbes to the growth and survival of a widespread pine under drought conditions. We found that specific beneficial fungus–host genotype combinations promoted drought tolerance in field and greenhouse studies. Drought tolerance, and associations with particular fungi, were passed from mother trees to their offspring, indicating the traits are genetic. These results demonstrate the interlinked importance of the genetics of a tree and its microbiome, which can be used to restore forest losses resulting from drought.
Premise of the study:
A transgenerational effect occurs when a biotic or abiotic environmental factor acts on a parental individual and thereby affects the phenotype of progeny. Due to the importance of transgenerational effects for understanding plant ecology and evolution, their underlying mechanisms are of general interest. Here, we introduce the concept that inherited symbiotic microorganisms could act as mechanisms of transgenerational effects in plants.
Methods:
We define the criteria required to demonstrate that transgenerational effects are microbially mediated and review evidence from the well-studied, vertically transmitted plant-fungal symbiosis (grass-Epichloë spp.) in support of such effects. We also propose a basic experimental design to test for the presence of adaptive transgenerational effects mediated by plant symbionts.
Key results:
An increasingly large body of literature shows that vertically transmitted microorganisms are common in plants, with potential to affect the phenotypes and fitness of progeny. Transgenerational effects could occur via parental modification of symbiont presence/absence, symbiont load, symbiont products, symbiont genotype or species composition, or symbiont priming. Several of these mechanisms appear likely in the grass-Epichloë endophytic symbiosis, as there is variation in the proportion of the progeny that carries the fungus, as well as variation in concentrations of mycelia and secondary compounds (alkaloids and osmolytes) in the seed.
Conclusions:
Symbiont-mediated transgenerational effects could be common in plants and could play large roles in plant adaptation to changing environments, but definitive tests are needed. We hope our contribution will spark new lines of research on the transgenerational effects of vertically transmitted symbionts in plants.
Seeds are involved in the transmission of microorganisms from one plant generation to another and consequently act as the initial inoculum for the plant microbiota. The purpose of this mini-review is to provide an overview of current knowledge on the diversity, structure and role of the seed microbiota. The relative importance of the mode of transmission (vertical vs horizontal) of the microbial entities composing the seed microbiota as well as the potential connections existing between seed and other plant habitats such as the anthosphere and the spermosphere is discussed. Finally the governing processes (niche vs neutral) involved in the assembly and the dynamics of the seed microbiota are examined.
Lophodermium comprises ascomycetous fungi that are both needle-cast pathogens and asymptomatic endophytes on a diversity of plant hosts. It is distinguished from other genera in the family Rhytismataceae by its filiform ascospores and ascocarps that open by a longitudinal slit. Nucleotide sequences of the internal transcribed spacer (ITS) region of nuclear ribosomal DNA were used to infer phylogenetic relationships within Lophodermium. Twenty-nine sequences from approximately 11 species of Lophodermium were analyzed together with eight sequences from isolates thought to represent six other genera of Rhytismataceae: Elytroderma, Lirula, Meloderma, Terriera, Tryblidiopsis and Colpoma. Two putative Meloderma desmazieresii isolates occurred within the Lophodermium clade but separate from one another, one grouped with L. indianum and the other with L. nitens. An isolate of Elytroderma deformans also occurred within the Lophodermium clade but on a solitary branch. The occurrence of these genera within the Lophodermium clade might be due to problems in generic concepts in Rhytismataceae, such as emphasis on spore morphology to delimit genera, to difficulty of isolating Rhytismataceae needle pathogens from material that also is colonized by Lophodermium or to a combination of both factors. We also evaluated the congruence of host distribution and several morphological characters on the ITS phylogeny. Lophodermium species from pine hosts formed a monophyletic sister group to Lophodermium species from more distant hosts from the southern hemisphere, but not to L. piceae from Picea. The ITS topology indicated that Lophodermium does not show strict cospeciation with pines at deeper branches, although several closely related isolates have closely related hosts. Pathogenic species occupy derived positions in the pine clade, suggesting that pathogenicity has evolved from endophytism. A new combination is proposed, Terriera minor (Tehon) P.R. Johnst.
The corvids of the southwest possess many adaptations for the harvest, transport, caching and recovery of pine seeds. However, there is a large degree of between-species variation in the distribution of these traits. These corvids have a well-accepted phylogeny (Hope, 1989), live within close proximity to one another and have relatively well-known natural histories. They therefore present an excellent opportunity to apply the comparative method (Kamil, 1988) to the study of these species differences (Balda et al., 1997). The comparative method for the study of adaptation and evolution of behavioral traits begins with a careful study of the natural histories of the study species which should reveal how a particular trait (or suite of traits) is utilized, and provide some information about the selective pressure and potential fitness which differentially influence the trait in the different species. Species differences (and similarities) in the use of the trait can be attributed to the ecology and/or phylogeny of the species. Two processes are particularly powerful in these types of investigations, convergence and divergence. Convergence leads to similarities among distantly related species owing to the influence of similar ecological constraints. Divergence leads to differences among closely related species that correlate with the influence of different ecological constraints. The strongest support for the evolution of a trait or set of traits is found when one can find patterns of convergence between distantly related groups and divergence between similar groups for a single suite of traits. Here, we examine the natural history of the various southwestern corvids with particular attention paid to the traits involved in seed harvest, caching and cache recovery.
Plants can no longer be considered as standalone entities and a more holistic perception is needed. Indeed, plants harbor a wide diversity of microorganisms both inside and outside their tissues, in the endosphere and ectosphere, respectively. These microorganisms, which mostly belong to Bacteria and Fungi, are involved in major functions such as plant nutrition and plant resistance to biotic and abiotic stresses. Hence, the microbiota impact plant growth and survival, two key components of fitness. Plant fitness is therefore a consequence of the plant per se and its microbiota, which collectively form a holobiont. Complementary to the reductionist perception of evolutionary pressures acting on plant or symbiotic compartments, the plant holobiont concept requires a novel perception of evolution. The interlinkages between the plant holobiont components are explored here in the light of current ecological and evolutionary theories. Microbiome complexity and the rules of microbiotic community assemblage are not yet fully understood. It is suggested that the plant can modulate its microbiota to dynamically adjust to its environment. To better understand the level of plant dependence on the microbiotic components, the core microbiota need to be determined at different hierarchical scales of ecology while pan‐microbiome analyses would improve characterization of the functions displayed.
Contents
Summary
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I.
Introduction
1196
II.
Plants as holobionts
1197
III.
Recruitment of the plant microbiota: what are the driving factors?
1198
IV.
The plant holobiont: an existing core plant microbiota?
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V.
The plant and its microbiome: what controls what?
1201
VI.
Concluding remarks and prospects
1204
Acknowledgements
1204
References
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Rhabdocline parkeri, an endophyte of Douglas fir, forms symptomless infections within single epidermal cells of healthy needles. Rhabdocline parkeri strains were isolated from trees growing in various habitats ranging from virgin old growth forests to a single young tree growing isolated in a meadow. Different genotypes of R. parkeri were distinguished by using the Random Amplified Polymorphic DNA (RAPD) technique. A significantly lower number of R. parkeri genotypes per unit foliage were isolated from trees within a 20-year-old managed stand and from an isolated tree than from old growth trees. Foliage from young trees (20 years old) in a stand directly adjacent to the sampled old growth trees showed levels of genotypic endophyte diversity comparable to that in the old growth trees. Genotypic diversity is estimated to be at least three orders of magnitude greater in foliage of the old growth trees and adjacent young trees than in foliage from the managed stand and from an isolated tree. This difference is ascribed to differences in tree age and access to inoculum.
Although the importance of plant-associated microorganisms for plant growth and health was getting more recognition recently, the role of seed-associated microorganisms, and especially seed endophytic bacteria, still is underestimated. Nevertheless, these
associations could be beneficial for germination and seedling establishment as seed endophytic bacteria are already present in these very early plant growth stages. Moreover, bacteria with beneficial characteristics can be selected by the plants and could be transferred via the seed to benefit the next generation.
In this paper, the current literature concerning bacterial endophytes that have been isolated from seeds of different plant species is reviewed. Their colonization routes, localization inside seeds and mode of transmission as well as their role and fate during germination and seedling development are discussed. At the end, some examples of bacterial seed endophytes with applications as a plant growthpromoting or biocontrol agent are given.
During three decades of research on conifer endophytes of the Acadian forest, numerous
insights have been gained in conifer-fungal ecology and secondary metabolite production.
Recently, we have explored endophyte assemblages of understory plants commonly
occurring with pine. Here we report for the first time the production of the potent antifungal
compound griseofulvin by a fungal endophyte isolated from eastern white pine
(Pinus strobus) needles and lowbush blueberry (Vaccinium angustifolium) stems from the
Acadian forest of New Brunswick and Nova Scotia, Canada. Maximum likelihood phylogenetic
analysis has placed the endophyte strains as an undescribed Xylaria sp. Our study
highlights the complexity of endophyte-host lifecycles and points to the existence of a
pine-blueberry ecotype. Aside from griseofulvin, piliformic acid was isolated from one of
the pine endophytes. This compound has been reported from Xylaria and related species
but not from Penicillium species known to produce griseofulvin.
Although the importance of plant-associated microbes is increasingly recognized, little is known about the biotic and abiotic factors that determine the composition of that microbiome. We examined the influence of plant genetic variation, and two stressors, one biotic and one abiotic, on the ectomycorrhizal (EM) fungal community of a dominant tree species, Pinus edulis. During three periods across 16 years that varied in drought severity, we sampled the EM fungal communities of a wild stand of P. edulis in which genetically based resistance and susceptibility to insect herbivory was linked with drought tolerance and the abundance of competing shrubs. We found that the EM fungal communities of insect-susceptible trees remained relatively constant as climate dried, while those of insect-resistant trees shifted significantly, providing evidence of a genotype by environment interaction. Shrub removal altered the EM fungal communities of insect-resistant trees, but not insect-susceptible trees, also a genotype by environment interaction. The change in the EM fungal community of insect-resistant trees following shrub removal was associated with greater shoot growth, evidence of competitive release. However, shrub removal had a 7-fold greater positive effect on the shoot growth of insect-susceptible trees than insect-resistant trees when shrub density was taken into account. Insect-susceptible trees had higher growth than insect-resistant trees, consistent with the hypothesis that the EM fungi associated with susceptible trees were superior mutualists. These complex, genetic-based interactions among species (tree-shrub-herbivore-fungus) argue that the ultimate impacts of climate change are both ecological and evolutionary.
The entomopathogenic fungus Beauveria bassiana commonly causes disease on a range of insects, including bark beetle pests of plantation forest trees. However, using broadcast application of the fungus to control pest beetles in large scale plantation forests could be difficult to achieve economically. B. bassiana has also been found as an endophyte in plants, including the main commercially planted tree in New Zealand, Pinus radiata. In this study we investigated two methods to establish B. bassiana as endophytes of pine seedlings, seed coating and root dip. Two isolates previously isolated from within mature pines were used and the seedlings monitored for 9 months. Samples of unwashed, washed and surface sterilised roots, surface sterilised needles and soil were plated on semi-selective agar at 2, 4 and 9 months after inoculation. B. bassiana was successfully established in pine seedlings using both root dip and seed coating. The fungus was found in soil, non-sterile and sterilised samples at 2 and 4 months, but only one seedling of 30 was positive for fungus in surface sterilised samples after 9 months.
The first developmental studies of Ascophyllum nodosum are presented in which zygote development is compared in thalli with and without endophytic Mycosphaerella ascophylli. In cultures where 24 h A. nodosum zygotes were inoculated with ascospores of M. ascophylli, 20-50% of the zygotes developed differently from control cultures without ascospores, with later infections (at 1-3 weeks) having little effect. Morphological differences were apparent within one month when infected thalli were ovoid and non-infected thalli were clavate. In addition, infected thalli were longer, had greater apical diameters, more apical hairs, and fewer and shorter rhizoids than non-infected thalli, the development of which more closely resembled other fucoid species. Differences between infected and non-infected individuals became more pronounced with development. After eight months there was a four-fold difference in thallus length, and morphologically transformed thalli had endophytic fungi. This transformation provides the first experimental evidence for an obligate, mutualistic symbiosis between A. nodosum and M. ascophylli.
Endophytic fungi were isolated from the interiors of surface-sterilized needles of balsam fir (Abies balsamea) and red spruce (Picea rubens) in New Brunswick, Canada. Four different fungi were isolated frequently. One species, designated X-W, was isolated exlusively from the petiole segment of red spruce needles. There was no difference in the variety of species isolated from fir needles from two sites, but a difference in frequency of species did exist. Micrographs of the interior of balsam fir needles showed hyphae occupying intercellular spaces and adhering to the outer walls of parenchyma cells. No penetration of cells by either fungus was observed.
Summary Induced by global warming, mountain plant species are migrating upwards. Species inhabiting the nival zone of today are threatened by competitors which move from the alpine zone towards the summits. The manner in which species move depends on their abilities to cope with microtopographical situations. We present a spatially explicit predictive model which draws scenarios of future species distribution patterns at a typical high mountain of the European Alps. The altitudinal temperature gradient is examined. Based on the lapse rate and on definitions of topographical niches of species, a +1 °C- and a +2 °C-warming scenario are modelled using a fine-scaled digital elevation model. Nival species will lose area and become restricted to specific topographical situations. Alpine and subnival grassland species are predicted to expand their area, mainly along stable surface situations. Whether the migration will take place as a filling or a moving process is specific to the particular species. Overall, biodiversity is apparently not threatened on the decadal scale. In special cases, however, genetic losses are likely both on a local and on a regional scale.
The distribution of foliar fungal endophytes within and between needles and trees of Pinus strobus L. (white pine) is largely unknown. In this study, needles were collected in Muskoka, Ontario, plated, and scored for hyphal outgrowth of endophytes to observe distributional patterns. Individual trees displayed different levels of infection but branches within those trees had similar levels. There was a large difference in the infection levels between the two extant needle age-classes, with the youngest needles being virtually endophyte-free. Needles divided into four sections exhibited the most hyphal outgrowth from the distal portion and the least from the medial-proximal portion. Cultural morphotypes were primarily of the Lophodermium and Hormonema morphologies. Lophodermium occurred at all positions along the needle but Hormonema was restricted to the proximal and distal portions. Infrequently occurring fungi of diverse morphotypes were found at all four needle positions. A separate experiment compared levels of endophyte infection between Muskoka trees and trees growing in an urban area (Guelph, Ontario). Needle pieces from Guelph hosts had low rates of infection (0.02%) compared with needle pieces from Muskoka hosts (66.5%). Thus, for white pine, foliar endophyte distribution is patchy within and between needles, trees, and locations, possibly reflecting differences in microhabitat or infection success.
Endophytes are fungi that form inapparent infections within leaves and stems of healthy plants. Closely related to virulent pathogens but with limited, if any, pathogenic effects themselves, many endophytes protect host plants from natural enemies. Animal herbivores and, in some cases, pathogenic microbes are poisoned by the mycotoxins produced by endophytes, "Constitutive mutualism' is the relatively faithful association, usually with grasses, of endophytes that infect host ovules and are propagated in host seed; substantial fungal biomass with probable high metabolic cost develops throughout the aerial parts of the host plant. "Inducible mutualist' endophytes are not involved with host seed and disseminate independently through air or in water. Infecting only vegetative parts of the host and remaining metabolically inactive for long periods with relatively little fungal biomass, inducible mutualists grow rapidly and produce toxins against herbivores when damaged host tissues provide new sites for infection. -from Author
Widespread piñon ( Pinus edulis ) mortality occurred across the southwestern USA during 2002–2003 in response to drought and bark beetle infestations. Given the recent mortality and changes in regional climate over the past several decades, there is a keen interest in post‐mortality regeneration dynamics in piñon–juniper woodlands.
Here, we examined piñon and Utah juniper ( Juniperus osteosperma ) recruitment at 30 sites across southwestern Colorado, USA that spanned a gradient of adult piñon mortality levels (10–100%) to understand current regeneration dynamics.
Piñon and juniper recruitment was greater at sites with more tree and shrub cover. Piñon recruitment was more strongly facilitated than juniper recruitment by trees and shrubs. New (post‐mortality) piñon recruitment was negatively affected by recent mortality. However, mortality had no effect on piñon advanced regeneration (juveniles established pre‐mortality) and did not shift juvenile piñon dominance.
Our results highlight the importance of shrubs and juniper trees for the facilitation of piñon establishment and survival. Regardless of adult piñon mortality levels, areas with low tree and shrub cover may become increasingly juniper dominated as a result of the few suitable microsites for piñon establishment and survival. In areas with high piñon mortality and high tree and shrub cover, our results suggest that piñon is regenerating via advanced regeneration.
Endophytic fungi were isolated from the needles of 45 species and varieties of the genus Pinus planted in an arboretum, and the species composition of the endophytes were compared among the pines examined. In general, Leptostroma spp. and Cenangium ferruginosum Fr. ex Fr. were dominant in the middle segment of the needle, while on the basal segment, Phialocephala sp. was more frequently isolated than the other two taxa. Leptostroma spp. seemed to be excluded from the basal segment by Phialocephala sp. The endophytic mycobiota of pines belonging to the same taxonomic group was similar. The taxonomic affinities of the host pines strongly affected the colonization patterns of the endophytes, while the effects of factors such as sampling date, tree age, and location in the stand were much weaker. Keywords: endophytic fungi, Pinus, host preference.
At a landscape level, endophyte distribution patterns are determined by host specificity, liquid precipitation, canopy cover, and geographic continuity or disjuctness. At the level of the individual stand or tree, height in the crown may become important. At the level of individual branch systems, age of substrate appears the most important factor. At a microscopic scale, tissue specificity, leaf topography, and phenology of the infection process with respect to leaf development all play a role. Endophytic fungi have seldom been found to cause widespread disease in trees; their age-specific infection frequencies in conifer needles shwo continuous increases with needle age, in contrast to needle pathogens in which infections are largely confined to young needles. Endophytes are usually viewed as protective mutualists acting against herbivorous insects and pathogenic fungi. Multiple infections of single leaves may lead to synergistic interactions of toxins produced by endophytes. Insect herbivores have evolved behavioral responses to the presence of endophytes, and protective mutualism by endophytes may occur only intermittently. -from Author
Endophytic fungi were isolated from black spruce (Picea mariana (Mill.) BSP) dormant buds and needles of four age-classes. Only one isolate was obtained from 400 buds. A total of 914 isolates were obtained from the needles. With increasing needle age the rate of colonization increased between current-year and 3-year-old needles from 4 to 90%, respectively. The needle segment attached to the twig was colonized more often (p < 0.05) than other segments overall and for 6 of the 11 taxa isolated. The first endophyte from current-year needles was isolated on July 14, 1988, but endophytes were obtained from needles of the other age-classes (1, 2, and 3 years) on all sampling dates between June 10 and September 16, 1988. Key words: endophyte, Picea mariana, dormand buds, needles.
Antiserum specific for Lophodermium piceae hyphae was obtained by absorbing a rabbit L. piceae antiserum with hyphal material of different fungal isolates. The specificity of this absorbed antiserum was tested with hyphae of endophytic fungi isolated from green, asymptomatic needles of Norway spruce (Picea abies Karst.) using the on-section immunogold labeling technique. With this specific, absorbed antiserum, a homogenous labeling was obtained with cultured hyphae of L. piceae, whereas all other spruce needle endophytes examined remained practically unlabeled. Insignificant cross-reactivity was also observed with needle tissues. The absorbed antiserum was then applied for the immunoelectron microscopical identification of L. piceae hyphae in situ in infected tissues of green, asymptomatic Norway spruce needles. The function of papillalike structures observed in infected needle mesophyll as well as the role of the hyphal sheath surrounding endophytic L. piceae hyphae are discussed in connection with the interaction between L. piceae and asymptomatic Norway spruce needles.
Quantitative estimates of frequencies of latent infections by Rhabdocline parkeri Sherw. on Douglas-fir were obtained by direct microscopy of cleared needles from three half-sib trees. The infections are intracellular and are confined to a single epidermal cell until the onset of needle senescence, a period of 2 – 5 years. Infection frequencies varied widely among trees but increase logarithmically with needle age on all three trees. Differences in infection frequencies among trees were not demonstrably related to levels of infestation by Contarinia spp., a needle-galling dipteran. Active colonization of the needle resumes at the onset of needle senescence, beginning with the production of haustoria in cells adjacent to the original infection sites. Rapid colonization of the needle and sporulation of R. parkeri coincide with needle abscission, occurring before substantial colonization of the needles by saprophytic fungi. Saprophytic fungi colonized needles rapidly following abscission, but R. parkeri was recoverable in culture from needles up to 35 days after abscission.
Endophytic fungi were isolated from foliage of four host species of Cupressaceae sampled from 19 sites in Oregon. Chamaecyparis lawsoniana and Thuja plicata showed high overall rates of infection (30–50%) while Calocedrus decurrens and Juniperus occidentalis showed lower rates (10–35%). For any particular host, samples from homogeneous stands with a closed canopy showed higher infection rates than those from mixed stands with an open canopy. For a given tree, infection rates tended to increase with increasing foliage age and decreasing distance from the trunk (exceptions are noted in the text below). The most commonly isolated endophytes include Linodochium sp. and Geniculosporium sp. on C. decurrens; Scolecosporiella sp., Nodulisporium sp., Geniculosporium sp., and Chloroscypha alutipes on C. lawsoniana; Retinocyclus abietis anamorph and Hormonema sp. on J. occidentalis; and Chloroscypha seaveri on T. plicata.
The incidence of internal fungal infections has been scored in coniferous needles from 19 hosts sampled in over 200 sites dispersed throughout western Oregon and southern Washington. Abies grandis, A. magnifica, Picea sitchensis, Pseudotsuga menziesii, and Sequoia sempervirens have proved congenial hosts for needle blade endophytes; petiole fungi are common in all species of Picea and Tsuga sampled. An undescribed taxon in the Hemiphacidiaceae, Chloroscypha spp., Cryptocline spp., Leptostroma spp., Naemacyclus spp., Phomopsis spp., Phyllosticta sp., and several unidentified Coelomycetes with Phoma-like spores were the dominant fungal taxa in the coniferous hosts sampled. The observed patterns of species dominance and diversity suggest that the true population of endophytes has been inadequately sampled in the present study and that an order of magnitude more intensive sampling might be required for real patterns of dominance and diversity to emerge. Many endophytes are restricted to a single coniferous host or to a restricted group of hosts. When similarity coefficients between coniferous species are computed on the basis of their internal needle microfloras, the resultant taxonomic groupings appear similar to those derived from consideration of conventional morphological criteria. Comparison of endophyte incidence with host distribution patterns for Pseudotsuga menziesii reveals that infection rates decrease at high elevations and dry sites.
Leaf endophytic fungi were isolated from 1 to 12-yr-old leaves of mature trees and basal sprouts of coastal redwood [Sequoia sempervirens (D. Don ex Lamb.) Endl.] in a redwood forest in Central California. Almost all samples yielded at least one species. The two most frequent species were Pleuroplaconema sp. and Cryptosporiopsis abietina Petrak. Among isolated taxa are endophytic generalists, species previously known as pathogens and a possible specialist. Species composition in leaves of progressing age in single branches revealed a patchy pattern of leaf colonization without an obvious sequence of succession. Changes in diversity and equitability in the endophytic community with leaf age are linked with differential distribution of some species in young versus old leaves and the increase in species richness in 4- and 5-yr-old leaves. The endophytic communities from leaves of trees and sprouts were generally similar, but with important differences in species richness and in distribution of Pleuroplaconema sp. and Pestalotiopsis funerea (Desm.) Stey. Principal component analysis based on endophytic frequency also indicated closeness of trees and sprouts as groups, but clearly separated each tree from its sprout. Differential susceptibility between trees and sprouts to endophytic infection is suggested on the basis of their endophytic communities.