Tricholoma matsutake in a natural Pinus densiflora forest: correspondence between above- and below-ground genets, association with multiple host trees and alteration of existing ectomycorrhizal communities

Death caps (Amanita phalloides) frequently establish from sexual spores, but individuals can grow large and live for more than a decade in invaded forests

Global change is reshaping Earth's biodiversity, but the changing distributions of nonpathogenic fungi remain largely undocumented, as do mechanisms enabling invasions. The ectomycorrhizal Amanita phalloides is native to Europe and invasive in North America. Using population genetics and genomics, we sought to describe the life history traits of this successfully invading symbiotic fungus. To test whether death caps spread underground using hyphae, or aboveground using sexual spores, we mapped and genotyped mushrooms from European and US sites. Larger genetic individuals (genets) would suggest spread mediated by vegetative growth, while many small genets would suggest dispersal mediated by spores. To test whether genets are ephemeral or persistent, we also sampled from populations over time. At nearly every site and across all time points, mushrooms resolve into small genets. Individuals frequently establish from sexual spores. But at one Californian site, a single individual measuring nearly 10 m across dominated. At two Californian sites, the same genetic individuals were discovered in 2004, 2014, and 2015, suggesting single individuals (both large and small) can reproduce repeatedly over relatively long timescales. A flexible life history strategy combining both mycelial growth and spore dispersal appears to underpin the invasion of this deadly perennial ectomycorrhizal fungus.

High diversity of fungal ecological groups in Andean-Patagonian Nothofagus forests

Native Andean-Patagonian Nothofagus forests harbour a unique diversity of microorganisms with diverse ecological roles. Although ectomycorrhizal associations constitute an important fragment of the biota associated with these forests, the factors affecting such communities are largely unknown. We investigated the biodiversity, relative abundance, and composition of ectomycorrhizal fungal communities in relation to two host tree species and ages and the soil properties in six monospecific and mixed evergreen-deciduous Nothofagus forests. We used the internal transcribed spacer (ITS2) region by sequencing 9,600 ectomycorrhizae (ECM) root tips for the identification of fungi. In total, 1,125 fungal taxa at the genus level distributed over 131 orders were identified. The phyla Ascomycota (34.5%) and Basidiomycota (62.1%) were the most abundant, whereas Mucoromycota (3.1%), Chytridiomycota, Cryptomycota, Olpidiomycota, and Zoopagomycota occurred less frequently. The highest taxon diversity was found in old trees, whereas young trees often exhibited a lower diversity of the associated fungi. The fungal taxa were grouped into seven broad ecological categories, of which saprotrophic associations were most common, followed by pathotrophic, pathotrophic-saprotrophic-symbiotrophic, pathotrophic-saprotrophic, and symbiotrophic associations. We did not detect significant differences in the number of taxa in each category between young and old N. dombeyi and N. obliqua. Overall, the scale of the Illumina sequencing approach allowed us to detect a fungal taxa diversity that would not be possible to find through surveys of fruiting bodies alone and that have never been observed in Nothofagus forests before. Our findings suggest the impact of the proximity between sites, the similarity of the soil conditions, and anthropogenic use of the forests on the belowground fungal community's diversity and composition. Furthermore, there were differences between above- and belowground occurrences of the edible mushrooms B. loyo and Ramaria spp. However, future research, including on EMC tips found beneath fairy rings could provide significantly better correlations with the occurrence of aboveground fruiting body.

Positive citation bias and overinterpreted results lead to misinformation on common mycorrhizal networks in forests

A common mycorrhizal network (CMN) is formed when mycorrhizal fungal hyphae connect the roots of multiple plants of the same or different species belowground. Recently, CMNs have captured the interest of broad audiences, especially with respect to forest function and management. We are concerned, however, that recent claims in the popular media about CMNs in forests are disconnected from evidence, and that bias towards citing positive effects of CMNs has developed in the scientific literature. We first evaluated the evidence supporting three common claims. The claims that CMNs are widespread in forests and that resources are transferred through CMNs to increase seedling performance are insufficiently supported because results from field studies vary too widely, have alternative explanations or are too limited to support generalizations. The claim that mature trees preferentially send resources and defence signals to offspring through CMNs has no peer-reviewed, published evidence. We next examined how the results from CMN research are cited and found that unsupported claims have doubled in the past 25 years; a bias towards citing positive effects may obscure our understanding of the structure and function of CMNs in forests. We conclude that knowledge on CMNs is presently too sparse and unsettled to inform forest management.

Warmer winters result in reshaping of the European beech forest soil microbiome (bacteria, archaea and fungi)-With potential implications for ecosystem functioning

In temperate regions, climate warming alters temperature and precipitation regimes. During winter, a decline in insulating snow cover changes the soil environment, where especially frost exposure can have severe implications for soil microorganisms and subsequently for soil nutrient dynamics. Here, we investigated winter climate change responses in European beech forests soil microbiome. Nine study sites with each three treatments (snow exclusion, insolation, and ambient) were investigated. Long-term adaptation to average climate was explored by comparing across sites. Triplicated treatment plots were used to evaluate short-term (one single winter) responses. Community profiles of bacteria, archaea and fungi were created using amplicon sequencing. Correlations between the microbiome, vegetation and soil physicochemical properties were found. We identify core members of the forest-microbiome and link them to key processes, for example, mycorrhizal symbiont and specialized beech wood degraders (fungi) and nitrogen cycling (bacteria, archaea). For bacteria, the shift of the microbiome composition due to short-term soil temperature manipulations in winter was similar to the community differences observed between long-term relatively cold to warm conditions. The results suggest a strong link between the changes in the microbiomes and changes in environmental processes, for example, nitrogen dynamics, driven by variations in winter climate.

The fall of the summer truffle: Recurring hot, dry summers result in declining fruitbody production of Tuber aestivum in Central Europe

Global warming is pushing populations outside their range of physiological tolerance. According to the environmental envelope framework, the most vulnerable populations occur near the climatic edge of their species' distributions. In contrast, populations from the climatic center of the species range should be relatively buffered against climate warming. We tested this latter prediction using a combination of linear mixed effects and machine learning algorithms on an extensive, citizen-scientist generated dataset on the fruitbody productivity of the Burgundy (aka summer) truffle (Tuber aestivum Vittad.), a keystone, ectomycorrhizal tree-symbiont occurring on a wide range of temperate climates. T. aestivum's fruitbody productivity was monitored at 3-week resolution over up to 8 continuous years at 20 sites distributed in the climatic center of its European distribution in southwest Germany and Switzerland. We found that T. aestivum fruitbody production is more sensitive to summer drought than would be expected from the breadth of its species' climatic niche. The monitored populations occurring nearly 5°C colder than the edge of their species' climatic distribution. However, interannual fruitbody productivity (truffle mass year^-1 ) fell by a median loss of 22% for every 1°C increase in summer temperature over a site's 30-year mean. Among the most productive monitored populations, the temperature sensitivity was even higher, with single summer temperature anomalies of 3°C sufficient to stop fruitbody production altogether. Interannual truffle productivity was also related to the phenology of host trees, with ~22 g less truffle mass for each 1-day reduction in the length of the tree growing season. Increasing summer drought extremes are therefore likely to reduce fruiting among summer truffle populations throughout Central Europe. Our results suggest that European T. aestivum may be a mosaic of vulnerable populations, sensitive to climate-driven declines at lower thresholds than implied by its species distribution model.

Cultivation studies of edible ectomycorrhizal mushrooms: successful establishment of ectomycorrhizal associations in vitro and efficient production of fruiting bodies

Most edible ectomycorrhizal mushrooms are harvested in forests or controlled tree plantations; examples include truffles, chanterelles, porcinis, saffron milk caps, and matsutake. This study explored recent advances in in vitro ectomycorrhizal cultivation of chanterelles and matsutakes for successful ectomycorrhizal seedling establishment and the subsequent manipulation of these seedlings for efficient fruiting body production. Chanterelle cultivation studies have been limited due to the difficulty of establishing pure cultures. However, once pure cultures were established in the Japanese yellow chanterelle (Cantharellus anzutake), its ectomycorrhizal manipulation produced fruiting bodies under controlled laboratory conditions. As C. anzutake strains have fruited repeatedly under ectomycorrhizal symbiosis with pine and oak seedlings, mating tests for the cross breeding are ongoing issues. As one of the established strains C-23 has full-genome sequence, its application for various type of ectomycorrhizal studies is also expected. By contrast, Tricholoma matsutake fruiting bodies have not yet been produced under controlled conditions, despite successful establishment of ectomycorrhizal seedlings. At present, the shiro structure of ≈1L in volume can be provided in two y incubation with pine hosts under controlled environmental conditions. Therefore, further studies that provides larger shiro on the host root system are desired for the outplantation trial and fruiting.

Ectomycorrhizal Networks in the Anthropocene: From Natural Ecosystems to Urban Planning

Trees acquire hydric and mineral soil resources through root mutualistic associations. In most boreal, temperate and Mediterranean forests, these functions are realized by a chimeric structure called ectomycorrhizae. Ectomycorrhizal (ECM) fungi are highly diversified and vary widely in their specificity toward plant hosts. Reciprocally, association patterns of ECM plants range from highly specialist to generalist. As a consequence, ECM symbiosis creates interaction networks, which also mediate plant-plant nutrient interactions among different individuals and drive plant community dynamics. Our knowledge of ECM networks essentially relies on a corpus acquired in temperate ecosystems, whereas the below-ground facets of both anthropogenic ECM forests and inter-tropical forests remain poorly investigated. Here, we successively (1) review the current knowledge of ECM networks, (2) examine the content of early literature produced in ECM cultivated forests, (3) analyze the recent progress that has been made in understanding the place of ECM networks in urban soils, and (4) provide directions for future research based on the identification of knowledge gaps. From the examined corpus of knowledge, we reach three main conclusions. First, the emergence of metabarcoding tools has propelled a resurgence of interest in applying network theory to ECM symbiosis. These methods revealed an unexpected interconnection between mutualistic plants with arbuscular mycorrhizal (AM) herbaceous plants, embedding ECM mycelia through root-endophytic interactions. This affinity of ECM fungi to bind VA and ECM plants, raises questions on the nature of the associated functions. Second, despite the central place of ECM trees in cultivated forests, little attention has been paid to these man-made landscapes and in-depth research on this topic is lacking. Third, we report a lag in applying the ECM network theory to urban soils, despite management initiatives striving to interconnect motile organisms through ecological corridors, and the highly challenging task of interconnecting fixed organisms in urban greenspaces is discussed. In particular, we observe a pauperized nature of resident ECM inoculum and a spatial conflict between belowground human pipelines and ECM networks. Finally, we identify the main directions of future research to make the needed link between the current picture of plant functioning and the understanding of belowground ECM networks.

Fungal Interactions Matter: Tricholoma matsutake Domination Affect Fungal Diversity and Function in Mountain Forest Soils

Tricholoma matsutake forms a symbiotic association with coniferous trees, developing mycelial aggregations, called 'shiro', which are characterized by distinct chemical and physical properties from nearby forest bulk soil. The fungal diversity living in shiro soil play key roles in nutrient cycles for this economically important mushroom, but have not been profiled across large spatial and environmental gradients. Samples of shiro and non-shiro (nearby bulk soil) were taken from five field sites where sporocarps naturally formed. Phospholipid fatty acids (PLFA) and Illumina MiSeq sequencing were combined to identify fungal biomass and community structure. Matsutake dominated in the shiro, which had a significantly reduced saprotrophic fungi biomass compared to non-shiro soil. Fungal diversity was negatively correlated with the relative abundance of T. matsutake in the shiro soil. The fungal community in the shiro was characterized by similar fungal species composition in most samples regardless of forest types. Matsutake coexisted with a specific fungal community due to competition or nutrient interactions. Oidiodendron was positively correlated with the abundance of T. matsutake, commonly cohabitant in the shiro. In contrast, Helotiales and Mortierella were negatively correlated with T. matsutake, both of which commonly inhabit the non-shiro soil but do not occur in shiro soils. We conclude that T. matsutake generate a dominance effect to shape the fungal community and diversity in shiro soil across distinctive forest types.

Metagenomic Analysis of Bacterial and Fungal Communities Inhabiting Shiro Dominant Soils of Two Production Regions of Tricholoma Matsutake S. Ito & S. Imai in Korea

Tricholoma matsutake is an ectomycorrhizal fungus that has obligate symbiotic relationships with Pinus densiflora. Its fruiting body has a distinctive flavor and is traded at a high price. Thus, it has been a significant source of income for rural communities in Korea. We hypothesized that biotic factors considerably influence the formation of the T. matsutake mushroom, and the soils producing T. matsutake share similar microbial characteristics. Therefore, the present study aimed to detect the specific fungal and bacterial groups in T. matsutake production soils (shiro+) and nonproduction soils (shiro−) of the Bonghwa and Yanyang regions via next-generation sequencing. In a total of 15 phyla, 36 classes, 234 genera of bacteria, six phyla, 29 classes, and 164 genera of fungi were detected from four samples at both sites. The species diversity of shiro+ soils was lower than the shiro− samples in both the fungal and bacterial groups. In addition, we did not find high similarities in the microbial communities between the shiro+ soils of the two regions. However, in the resulting differences between the fungal communities categorized by their trophic assembly, we found a distinguishable compositional pattern in the fungal communities from the shiro+ soils and the shiro− soils of the two sites. Thus, the similarity among the microbial communities in the forest soils may be due to the fact that the microbial communities in the T. matsutake dominant soils are closely associated with biotic factors and abiotic factors such as soil properties.

Four new species of Hydnellum (Thelephorales, Basidiomycota) with a note on Sarcodon illudens

Four new Hydnellum species are described. Hydnellum roseoviolaceum sp. nov. grows in dry pine heaths on acidic, sandy soil. It is close to H. fuligineoviolaceum, another pine-associated species, but differs by smaller spores, an initially rose-coloured instead of violet flesh in fresh basidiomata and a mild taste. Hydnellum scabrosellum sp. nov. grows in coniferous forests on calcareous soil. It shares a general morphology with H. scabrosum, which also is its closest relative. It differs by having smaller and slenderer basidiomata and by the yellowish ochraceous colour of flesh and spines in dried specimens compared to the whitish or reddish brown colour seen in H. scabrosum. Hydnellum fagiscabrosum sp. nov. is another species with morphological and phylogenetic affinities to H. scabrosum. However, it is associated with trees from Fagales whereas H. scabrosum is associated with Pinaceae. Hydnellum nemorosum sp. nov. is yet another species that associates with broadleaved trees. It seems to be a rare species, morphologically reminiscent of H. fuligineoviolaceum, H. ioeides and H. scabrosum, but it is phylogenetically close to H. fennicum. Sequences from the type specimens of H. glaucopus, H. lepidum, H. scabrosum, Sarcodon illudens and S. regalis are included in the analyses. Specimens given the provisional name "Sarcodon pseudoglaucopus" in Sweden are now shown to be referable to S. illudens. The analyses further showed that S. illudens is close to H. lepidum. The new combination Hydnellum illudens is proposed. Sarcodon regalis and H. lepidum are shown to be conspecific and, although their basionyms were simultaneously published, the name S. regalis was only validated in a later publication. Hydnellum lepidum therefore takes priority and S. regalis becomes a synonym. Citation: Nitare J, Ainsworth AM, Larsson E, Parfitt D, Suz LM, Svantesson S, Larsson K-H (2021). Four new species of Hydnellum (Thelephorales, Basidiomycota) with a note on Sarcodon illudens. Fungal Systematics and Evolution 7: 233-254. doi: 10.3114/fuse.2021.07.12.

Pyrosequencing and Taxonomic Composition of the Fungal Community from Soil of Tricholoma matsutake in Gyeongju

Tricholoma matsutake is an ectomycorrhizal fungus that has a symbiotic relationship with the root of Pinus densiflora. Soil microbial communities greatly affect the growth of T. matsutake, however, few studies have examined the characteristics of these communities. In the present study, we analyzed soil fungal communities from Gyeongju and Yeongdeok using metagenomic pyrosequencing to investigate differences in fungal species diversity, richness, and taxonomic composition between the soil under T. matsutake fruiting bodies (Sample 2) and soil where the fairy ring of T. matsutake was no longer present (Sample 1). The same spot was investigated three times at intervals of four months to observe changes in the community. In the samples from Yeongdeok, the number of valid reads was lower than that at Gyeongju. The operational taxonomic units of most Sample 2 groups were less than those of Sample 1 groups, indicating that fungal diversity was low in the T. matsutakedominant soil. The soil under the T. matsutake fruiting bodies was dominated by more than 51% T. matsutake. From fall to the following spring, the ratio of T. matsutake decreased. Basidiomycota was the dominant phylum in most samples. G-F1-2, G-F2-2, and Y-F1-2 had the genera Tricholoma, Umbelopsis, Oidiodendron, Sagenomella, Cladophialophora, and Phialocephala in common. G-F1-1, G-F2-1, and Y-F1-1 had 10 genera including Umbelopsis and Sagenomella in common. From fall to the following spring, the amount of phyla Basidiomycota and Mucoromycota gradually decreased but that of phylum Ascomycota increased. We suggest that the genus Umbelopsis is positively related to T. matsutake.

Spore germination and ectomycorrhizae formation of Tricholoma matsutake on pine root systems with previously established ectomycorrhizae from a dikaryotic mycelial isolate of T. matsutake

In vitro ectomycorrhizal synthesis of Tricholoma matsutake with host plants has been widely conducted to elucidate fungal symbiotic properties for future cultivation practices. Here, we report on the importance of basidiospore inocula for this fungus to provide ectomycorrhizal seedlings in vitro. Ectomycorrhizal pine seedlings synthesized in vitro with cultured mycelium of T. matsutake (isolate #45 or #84) in a 250-mL culture vessel (soil volume) were transplanted to a large 1-L culture vessel. Fresh basidiospores of this fungus were aseptically inoculated on the ectomycorrhizal root system. The ectomycorrhizal seedlings in the 1-L vessel were grown for 9 months, and some plants were further grown for 6 more months under non-aseptic conditions in 4.1-L jars. The ectomycorrhizal seedlings previously inoculated with isolate #84 in the 1-L vessel showed significant ectomycorrhizal biomass (mycorrhizal root length) after spore inoculation. The ectomycorrhizal seedlings in the 4.1-L vessel showed large shiro structures (> 10 cm in diameter). PCR amplification of intergenic spacer 1 of the rRNA gene and long terminal repeat retroelement of T. matsutake in ectomycorrhizal root tips in both the 1-L vessels and 4.1-L jars revealed the presence of amplicons of the previously inoculated culture isolate of T. matsutake and the new genet(s) that established via germination of the inoculated basidiospores. This is the first report that inoculated basidiospores of T. matsutake germinated and colonized the host root to generate ectomycorrhizae in vitro.

Genetic analysis of Boletus edulis suggests that intra-specific competition may reduce local genetic diversity as a woodland ages

Ectomycorrhizal fungi are key players in terrestrial ecosystems yet their mating systems and population dynamics remain poorly understood. We investigated the fine-scale relatedness structure and genetic diversity of Boletus edulis, one of the world's most commercially important wild mushrooms. Microsatellite genotyping of fruiting bodies from 14 different sites around Bielefeld in Germany revealed little in the way of population structure over a geographic scale of several kilometres. However, on a more local scale we found evidence for elevated relatedness as well as inbreeding. We also observed a significant negative association between the genetic diversity of fruit and the age of the trees under which they were sampled. Taken together, our results suggest that as genets mature, they compete and potentially create conditions under which further spores struggle to become established. By implication, even though this species is widely picked, propagules remain common enough to create strong competition when new habitats become available.

Bioactive properties of streptomyces may affect the dominance of Tricholoma matsutake in shiro

Tricholoma matsutake is known to be the dominant fungal species in matsutake fruitbody neighboring (shiro) soil. To understand the mechanisms behind matsutake dominance, we studied the bacterial communities in matsutake dominant shiro soil and non-shiro soil, isolated the strains of Streptomyces from matsutake mycorrhizal root tips both from shiro soil and from the Pinus densiflora seedlings cultivated in shiro soil. Further, we investigated three Streptomyces spp. for their ability to inhibit fungal growth and Pinus densiflora seedling root elongation as well as two strains for their antifungal and antioxidative properties.

Our results showed that Actinobacteria was the most abundant phylum in shiro soil. However, the differences in the Actinobacterial community composition (phylum or order level) between shiro and non-shiro soils were not significant, as indicated by PERMANOVA analyses. A genus belonging to Actinobacteria, Streptomyces, was present on the matsutake mycorrhizas, although in minority. The two antifungal assays revealed that the broths of three Streptomyces spp. had either inhibitory, neutral or promoting effects on the growth of different forest soil fungi as well as on the root elongation of the seedlings. The extracts of two strains, including one isolated from the P. densiflora seedlings, inhibited the growth of either pathogenic or ectomycorrhizal fungi. The effect depended on the medium used to cultivate the strains, but not the solvent used for the extraction. Two Streptomyces spp. showed antioxidant activity in one out of three assays used, in a ferric reducing antioxidant power assay. The observed properties seem to have several functions in matsutake shiro soil and they may contribute to the protection of the shiro area for T. matsutake dominance.

Biosynthesis of (R)-(-)-1-Octen-3-ol in Recombinant Saccharomyces cerevisiae with Lipoxygenase-1 and Hydroperoxide Lyase Genes from Tricholoma matsutake

Tricholoma matsutake is an ectomycorrhizal fungus, related with the host of Pinus densiflora. Most of studies on T. matsutake have focused on mycelial growth, genes and genomics, phylogenetics, symbiosis, and immune activity of this strain. T. matsutake is known for its unique fragrance in Eastern Asia. The most major component of its scent is (R)-(-)-1-octen-3-ol and is biosynthesized from the substrate linoleic acid by the sequential reaction of lipoxygenase and peroxide lyase. Here, we report for the first time the biosynthesis of (R)-(-)- 1-octen-3-ol of T. matsutake using the yeast Saccharomyces cerevisiae as a host. In this study, cDNA genes correlated with these reactions were cloned from T. matsutake, and expression studies of theses genes were carried out in the yeast Saccharomyces cerevisiae. The product of these genes expression study was carried out with Western blotting. The biosynthesis of (R)-(-)- 1-octen-3-ol of T. matsutake in recombinant Saccharomyces cerevisiae was subsequently identified with GC-MS chromatography analysis. The biosynthesis of (R)-(-)-1-octen-3-ol with S. cerevisiae represents a significant step forward.

The effects of co-colonising ectomycorrhizal fungi on mycorrhizal colonisation and sporocarp formation in Laccaria japonica colonising seedlings of Pinus densiflora

Forest trees are colonised by different species of ectomycorrhizal (ECM) fungi that interact competitively or mutualistically with one another. Most ECM fungi can produce sporocarps. To date, the effects of co-colonising fungal species on sporocarp formation in ECM fungi remain unknown. In this study, we examined host plant growth, mycorrhizal colonisation, and sporocarp formation when roots of Pinus densiflora are colonised by Laccaria japonica and three other ECM fungal species (Cenococcum geophilum, Pisolithus sp., and Suillus luteus). Sporocarp numbers were recorded throughout the experimental period. The biomass, photosynthetic rate, and mycorrhizal colonisation rate of the seedlings were also measured at 45 days, 62 days, and 1 year after seedlings were transplanted. Results indicated that C. geophilum and S. luteus may negatively impact mycorrhizal colonisation and sporocarp formation in L. japonica. Sporocarp formation in L. japonica was positively correlated with conspecific mycorrhizal colonisation but negatively correlated with the biomass of seedlings of P. densiflora. The co-occurring ECM fungi largely competed with L. japonica, resulting in various effects on mycorrhizal colonisation and sporocarp formation in L. japonica. A variety of mechanisms may be involved in the competitive interactions among the different ECM fungal species, including abilities to more rapidly colonise root tips, acquire soil nutrients, or produce antibiotics. These mechanisms need to be confirmed in further studies.

Factors Influencing Leaf- and Root-Associated Communities of Bacteria and Fungi Across 33 Plant Orders in a Grassland

In terrestrial ecosystems, plants interact with diverse taxonomic groups of bacteria and fungi in the phyllosphere and rhizosphere. Although recent studies based on high-throughput DNA sequencing have drastically increased our understanding of plant-associated microbiomes, we still have limited knowledge of how plant species in a species-rich community differ in their leaf and root microbiome compositions. In a cool-temperate semi-natural grassland in Japan, we compared leaf- and root-associated microbiomes across 137 plant species belonging to 33 plant orders. Based on the whole-microbiome inventory data, we analyzed how sampling season as well as the taxonomy, nativeness (native or alien), lifeform (herbaceous or woody), and mycorrhizal type of host plants could contribute to variation in microbiome compositions among co-occurring plant species. The data also allowed us to explore prokaryote and fungal lineages showing preferences for specific host characteristics. The list of microbial taxa showing significant host preferences involved those potentially having some impacts on survival, growth, or environmental resistance of host plants. Overall, this study provides a platform for understanding how plant and microbial communities are linked with each other at the ecosystem level.

Tricholoma matsutake may take more nitrogen in the organic form than other ectomycorrhizal fungi for its sporocarp development: the isotopic evidence

Tricholoma matsutake is an ectomycorrhizal (ECM) fungus capable of in vitro saprotrophic growth, but the sources of C and N used to generate sporocarps in vivo are not well understood. We examined natural abundance isotope data to investigate this phenomenon. For this purpose, C, N and their stable isotopes (13C, 15N) content of fungal sporocarps and their potential nutrient sources (i.e., foliage, litter, fine roots, wood, and soil) were investigated from two well-studied sites in Finland and Japan. Our results show that δ13C values of T. matsutake and other fungal groups are consistent with those of most studies, but a very high δ15N value (16.8‰ ± 2.3) is observed in T. matsutake. Such isotopic pattern of fungal δ15N suggests that matsutake has a greater proteolytic potential to digest chemically complex 15N-enriched organic matter and hydrophobic hyphae. This assumption is further supported by a significant and positive correlation between δ13Ccap-stipe and δ15Ncap-stipe exclusively in T. matsutake, which suggests common C and N sources (protein) possible for isotopically enriched cap. The 13C increase of caps relative to stipe presumably reflects greater contents of 13C-enriched protein than 13C-depleted chitin. We conclude that T. matsutake is a typical ECM fungus which obtains for its sporocarp development for both C and N from a common protein source (vs. photosynthetic carbon) present in soil organic matter.

Temperature niche position and breadth of ectomycorrhizal fungi: Reduced diversity under warming predicted by a nested community structure

Species with narrow niche breadths are assumed to be more susceptible to environmental changes than those with wide niche breadths. Although information on niche properties is necessary for predicting biological responses to environmental changes, such information is largely missing for soil microbes. In this study, we present the temperature niche positions and breadths of a functionally important group of eukaryotic soil microbes, ectomycorrhizal (EM) fungi. We compiled high-quality EM fungal sequence data from 26 forested sites in Japan (with mean annual temperatures ranging from 1.6 to 23.6°C) to create temperature niche profiles for each individual fungal species. Nested theory and a newly developed weighted-randomization null model were applied to 75 fungal operational taxonomic units (OTUs) with high occurrence records to examine potential preferences for certain temperature positions and breadths. Our analyses revealed that (a) many EM fungal OTUs were restricted to habitats with low mean annual temperatures, (b) fungal OTUs observed at colder sites exhibited narrower temperature breadths than expected by chance, (c) the composition of EM fungal OTUs exhibited a nested pattern along the temperature gradient, and (d) EM fungal richness was highest at colder sites, where the greatest degree of overlap in OTU occurrence was observed. These findings imply that future warming may limit the distribution of many EM fungal species that are currently adapted to only cold climates. This could eventually reduce EM fungal biodiversity, which is linked to forest function through symbiotic associations with trees. This study demonstrates the distribution and environmental ranges of various EM fungal species and can contribute to develop species distribution models with the aim of conserving microbes in the face of climate change.

Diversity and effect of Trichoderma isolated from the roots of Pinus densiflora within the fairy ring of pine mushroom (Tricholoma matsutake)

Pine mushroom (PM, Tricholoma matsutake) is an important ectomycorrhizal fungus in Asia primarily due to its value as a food delicacy. Recent studies have shown that fairy rings of PM have distinctive fungal communities, which suggests that other fungi influence the growth of PM. Trichoderma is a well-known saprotrophic fungus commonly found in pine roots within PM fairy rings; however, little is known about the diversity of Trichoderma associated with PM and how these species influence PM growth. This study focused on diversity of Trichoderma isolated from pine roots within PM fairy rings and how these species affect the growth of PM isolate. Based on tef1a phylogenetic analyses, nine Trichoderma species (261 isolates) were identified. Trichoderma songyi and T. spirale were the dominant species, and Trichoderma community varied geographically. Growth experiments indicated that metabolites from five Trichoderma species had a significant influence on the growth of PM isolates. Metabolites of two Trichoderma species increased PM growth, while those of three Trichoderma species suppressed the growth. Within the fairy rings, Trichoderma that had a positive or neutral effect comprised the majority of Trichoderma communities. The results of this study suggest that various Trichoderma species co-exist within PM fairy rings and that these species influence PM growth.

Recent Insights on Biological and Ecological Aspects of Ectomycorrhizal Fungi and Their Interactions

The roots of most terrestrial plants are colonized by mycorrhizal fungi. They play a key role in terrestrial environments influencing soil structure and ecosystem functionality. Around them a peculiar region, the mycorrhizosphere, develops. This is a very dynamic environment where plants, soil and microorganisms interact. Interest in this fascinating environment has increased over the years. For a long period the knowledge of the microbial populations in the rhizosphere has been limited, because they have always been studied by traditional culture-based techniques. These methods, which only allow the study of cultured microorganisms, do not allow the characterization of most organisms existing in nature. The introduction in the last few years of methodologies that are independent of culture techniques has bypassed this limitation. This together with the development of high-throughput molecular tools has given new insights into the biology, evolution, and biodiversity of mycorrhizal associations, as well as, the molecular dialog between plants and fungi. The genomes of many mycorrhizal fungal species have been sequenced so far allowing to better understanding the lifestyle of these fungi, their sexual reproduction modalities and metabolic functions. The possibility to detect the mycelium and the mycorrhizae of heterothallic fungi has also allowed to follow the spatial and temporal distributional patterns of strains of different mating types. On the other hand, the availability of the genome sequencing from several mycorrhizal fungi with a different lifestyle, or belonging to different groups, allowed to verify the common feature of the mycorrhizal symbiosis as well as the differences on how different mycorrhizal species interact and dialog with the plant. Here, we will consider the aspects described before, mainly focusing on ectomycorrhizal fungi and their interactions with plants and other soil microorganisms.

Heavy-ion beam mutagenesis of the ectomycorrhizal agaricomycete Tricholoma matsutake that produces the prized mushroom "matsutake" in conifer forests

Tricholoma matsutake is an ectomycorrhizal agaricomycete that produces the prized mushroom "matsutake" in Pinaceae forests. Currently, there are no available cultivars or cultivation methods that produce fruiting bodies. Heavy-ion beams, which induce mutations through double-stranded DNA breaks, have been used widely for plant breeding. In the present study, we examined whether heavy-ion beams could be useful in isolating T. matsutake mutants. An argon-ion beam gave a suitable lethality curve in relation to irradiation doses, accelerating killing at 100-150 Gy. Argon-ion beam irradiation of the agar plate cultures yielded several transient mutants whose colony morphologies differed from that of the wild-type strain at the first screening, but which did not persist following culture transfer. It also generated a mutant whose phenotype remained stable after repeated culture transfers. The stable pleiotropic mutant not only exhibited a different colony morphology to the wild type, but also showed increased degradation of dye-linked water-insoluble amylose and cellulose substrates. Thus, heavy-ion beams may be useful for isolating mutants of T. matsutake, although precautions may be required to maintain the mutants, without phenotypic reversion, during repetitive culture of their mycelia.

Ectomycorrhization of Tricholoma matsutake with Quercus aquifolioides affects the endophytic microbial community of host plant

Tricholoma matsutake (S. Ito et Imai) is an ectomycorrhizal basidiomycete associated with Pinaceae and Fagaceae trees in the Northern Hemisphere. It is still unknown whether the symbiotic relationship with this ectomycorrhiza could affect the host plant's endophytic microbial community. In this study, we used high throughput sequencing to analyze the endophytic microbial communities of different Quercus aquifolioides tissues with or without T. matsutake partner. About 35,000 clean reads were obtained per sample, representing 34 bacterial phyla and 7 fungal phyla. We observed 3980 operational taxonomic units (OTUs) of bacteria and 457 OTUs of fungi at a 97% similarity level. Three bacterial phyla, Proteobacteria, Cyanobacteria, and Bacteroidetes, and the fungal phylum Ascomycota were dominant in all tissues. The relative abundance of these taxa differed significantly between Q. aquifolioides tissues with and without T. matsutake partner (p < 0.05). The bacterial genus Pseudomonas and the fungal genus Cryptosporiopsis were more abundant in mycorrhized roots than in control roots. This study showed that the community structure and dominant species of endophytic microbial communities in Q. aquifolioides tissues might be altered by colonization with T. matsutake. This work provides a new insight into the interactions between ectomycorrhizal fungus and host plant.

Root-associated fungal communities in three Pyroleae species and their mycobiont sharing with surrounding trees in subalpine coniferous forests on Mount Fuji, Japan

Pyroleae species are perennial understory shrubs, many of which are partial mycoheterotrophs. Most fungi colonizing Pyroleae roots are ectomycorrhizal (ECM) and share common mycobionts with their Pyroleae hosts. However, such mycobiont sharing has neither been examined in depth before nor has the interspecific variation in sharing among Pyroleae species. Here, we examined root-associated fungal communities in three co-existing Pyroleae species, including Pyrola alpina, Pyrola incarnata, and Orthilia secunda, with reference to co-existing ECM fungi on the surrounding trees in the same soil blocks in subalpine coniferous forests. We identified 42, 75, and 18 fungal molecular operational taxonomic units in P. alpina, P. incarnata, and O. secunda roots, respectively. Mycobiont sharing with surrounding trees, which was defined as the occurrence of the same mycobiont between Pyroleae and surrounding trees in each soil block, was most frequent among P. incarnata (31 of 44 plants). In P. alpina, sharing was confirmed in 12 of 37 plants, and the fungal community was similar to that of P. incarnata. Mycobiont sharing was least common in O. secunda, found in only 5 of 32 plants. Root-associated fungi of O. secunda were dominated by Wilcoxina species, which were absent from the surrounding ECM roots in the same soil blocks. These results indicate that mycobiont sharing with surrounding trees does not equally occur among Pyroleae plants, some of which may develop independent mycorrhizal associations with ECM fungi, as suggested in O. secunda at our research sites.

Local-Level Genetic Diversity and Structure of Matsutake Mushroom (Tricholoma matsutake) Populations in Nagano Prefecture, Japan, Revealed by 15 Microsatellite Markers

The annual yield of matsutake mushrooms (Tricholoma matsutake) has consistently decreased in Japan over the past few decades. We used 15 polymorphic and codominant simple sequence repeat (SSR) markers, developed using next-generation sequencing, to carry out genetic analyses of 10 populations in Nagano, Japan. Using the SSRs, we identified 223 genotypes, none of which was observed in more than one population. The mean expected heterozygosity and standardized allelic richness values were 0.67 and 4.05, respectively. Many alleles appeared in only one of the 10 populations; 34 of these private alleles were detected with a mean number per population of 3.4. The fixation index (F_ST) and standardized genetic differentiation (G′_ST) values were 0.019 and 0.028, respectively. Analysis of molecular variance (AMOVA) showed that the contribution of among population, among genets within a population, and within genets variation to the total variation was 2.91%, 11.62%, and 85.47%, respectively, with genetic differentiation being detected for all sources. Twenty-eight of 45 pairwise F_ST values were significantly larger than zero, and no pattern of isolation by distance was detected among the 10 populations. Bayesian-based clustering did not show clear differences among populations. These results suggest that reestablishment of a colony would be best accomplished by transplantation within a field; if this is not possible, then transplantation from within several dozen kilometers will cause little damage to the original population genetic structure.

Distinctive Feature of Microbial Communities and Bacterial Functional Profiles in Tricholoma matsutake Dominant Soil

Tricholoma matsutake, the pine mushroom, is a valuable forest product with high economic value in Asia, and plays an important ecological role as an ectomycorrhizal fungus. Around the host tree, T. matsutake hyphae generate a distinctive soil aggregating environment called a fairy ring, where fruiting bodies form. Because T. matsutake hyphae dominate the soil near the fairy ring, this species has the potential to influence the microbial community. To explore the influence of T. matsutake on the microbial communities, we compared the microbial community and predicted bacterial function between two different soil types-T. matsutake dominant and T. matsutake minor. DNA sequence analyses showed that fungal and bacterial diversity were lower in the T. matsutake dominant soil compared to T. matsutake minor soil. Some microbial taxa were significantly more common in the T. matsutake dominant soil across geographic locations, many of which were previously identified as mycophillic or mycorrhiza helper bacteria. Between the two soil types, the predicted bacterial functional profiles (using PICRUSt) had significantly distinct KEGG modules. Modules for amino acid uptake, carbohydrate metabolism, and the type III secretion system were higher in the T. matsutake dominant soil than in the T. matsutake minor soil. Overall, similar microbial diversity, community structure, and bacterial functional profiles of the T. matsutake dominant soil across geographic locations suggest that T. matsutake may generate a dominance effect.

A qPCR assay that specifically quantifies Tricholoma matsutake biomass in natural soil

Tricholoma matsutake is an ectomycorrhizal basidiomycete that produces prized, yet uncultivable, "matsutake" mushrooms along densely developed mycelia, called "shiro," in the rhizosphere of coniferous forests. Pinus densiflora is a major host of this fungus in Japan. Measuring T. matsutake biomass in soil allows us to determine the kinetics of fungal growth before and after fruiting, which is useful for analyzing the conditions of the shiro and its surrounding mycorrhizosphere, predicting fruiting timing, and managing forests to obtain better crop yields. Here, we document a novel method to quantify T. matsutake mycelia in soil by quantifying a single-copy DNA element that is uniquely conserved within T. matsutake but is absent from other fungal species, including close relatives and a wide range of ectomycorrhizal associates of P. densiflora. The targeted DNA region was amplified quantitatively in cultured mycelia that were mixed with other fungal species and soil, as well as in an in vitro co-culture system with P. densiflora seedlings. Using this method, we quantified T. matsutake mycelia not only from shiro in natural environments but also from the surrounding soil in which T. matsutake mycelia could not be observed by visual examination or distinguished by other means. It was demonstrated that the core of the shiro and its underlying area in the B horizon are predominantly composed of fungal mycelia. The fungal mass in the A or A₀ horizon was much lower, although many white mycelia were observed at the A horizon. Additionally, the rhizospheric fungal biomass peaked during the fruiting season.

Molecular and morphological analyses confirm Rhizopogon verii as a widely distributed ectomycorrhizal false truffle in Europe, and its presence in South America

The genus Rhizopogon includes species with hypogeous or subepigeus habit, forming ectomycorrhizae with naturally occurring or planted pines (Pinaceae). Species of the genus Rhizopogon can be distinguished easily from the other hypogeous basidiomycetes by their lacunose gleba without columella and their smooth elliptical spores; however, the limit between species is not always easy to establish. Rhizopogon luteolus, the type species of the genus, has been considered one of the species that are more abundant in Europe, as well as it has been cited in pine plantation of North and South America, different parts of Africa, Australia, and New Zealand. However, in this study, based on molecular analyses of the ITS nuclear ribosomal DNA (nrDNA) sequences (19 new sequences; 37 sequences from GenBank/UNITE, including those from type specimens), we prove that many GenBank sequences under R. luteolus were misidentified and correspond to Rhizopogon verii, a species described from Tunisia. Also, we confirm that basidiomes and ectomycorrhizae recently collected in Germany under Pinus sylvestris, as well as specimens from South of Brazil under Pinus taeda belong to R. verii. Thanks to the numerous ectomycorrhizal tips collected in Germany, a complete description of R. verii/P. sylvestris ectomycorrhiza is provided. Moreover, since in this paper the presence of R. verii in South America is here reported for the first time, a short description of basidiomes collected in Brazil, compared with collections located in different European herbaria, is included.

Pathway and sink activity for photosynthate translocation in Pisolithus extraradical mycelium of ectomycorrhizal Pinus thunbergii seedlings

The purpose of this study was to identify the pathway and sink activity of photosynthate translocation in the extraradical mycelium (ERM) of a Pisolithus isolate. We labelled ectomycorrhizal (ECM) Pinus thunbergii seedlings with (14)CO2 and followed (14)C distribution within the ERM by autoradiography. (14)C photosynthate translocation in the ERM resulted in (14)C distribution in rhizomorphs throughout the ERM, with (14)C accumulation at the front. When most radial mycelial connections between ECM root tips and the ERM front were cut, the whole allocation of (14)C photosynthates to the ERM was reduced. However, the overall pattern of (14)C distribution in the ERM was maintained even in regions immediately above and below the cut, with no local (14)C depletion or accumulation. We inferred from this result that every portion in the ERM has a significant sink activity and a definite sink capacity for photosynthates and that photosynthates detour the cut and reach throughout the ERM by translocation in every direction. Next, we prepared paired ECM seedlings, ERMs of which had been connected with each other by hyphal fusion, alongside, labelled the left seedling with (14)CO2, and shaded none, one or both of them. (14)C photosynthates were acropetally and basipetally translocated from the left ERM to ECM root tips of the right seedling through rhizomorphs in the left and right ERMs, respectively. With the left seedling illuminated, (14)C translocation from the left to the right ERM increased by shading the right seedling. This result suggests that reduced photosynthate transfer from the host to its ERM increased sink activity of the ERM.

Variation in ectomycorrhizal fungal communities associated with Oreomunnea mexicana (Juglandaceae) in a Neotropical montane forest

Neotropical montane forests are often dominated by ectomycorrhizal (EM) tree species, yet the diversity of their EM fungal communities remains poorly explored. In lower montane forests in western Panama, the EM tree species Oreomunnea mexicana (Juglandaceae) forms locally dense populations in forest otherwise characterized by trees that form arbuscular mycorrhizal (AM) associations. The objective of this study was to compare the composition of EM fungal communities associated with Oreomunnea adults, saplings, and seedlings across sites differing in soil fertility and the amount and seasonality of rainfall. Analysis of fungal nrITS DNA (nuclear ribosomal internal transcribed spacers) revealed 115 EM fungi taxa from 234 EM root tips collected from adults, saplings, and seedlings in four sites. EM fungal communities were equally species-rich and diverse across Oreomunnea developmental stages and sites, regardless of soil conditions or rainfall patterns. However, ordination analysis revealed high compositional turnover between low and high fertility/rainfall sites located ca. 6 km apart. The EM fungal community was dominated by Russula (ca. 36 taxa). Cortinarius, represented by 14 species and previously reported to extract nitrogen from organic sources under low nitrogen availability, was found only in low fertility/high rainfall sites. Phylogenetic diversity analyses of Russula revealed greater evolutionary distance among taxa found on sites with contrasting fertility and rainfall than was expected by chance, suggesting that environmental differences among sites may be important in structuring EM fungal communities. More research is needed to evaluate whether EM fungal taxa associated with Oreomunnea form mycorrhizal networks that might account for local dominance of this tree species in otherwise diverse forest communities.

De Novo Transcriptome Sequencing Analysis of cDNA Library and Large-Scale Unigene Assembly in Japanese Red Pine (Pinus densiflora)

Japanese red pine (Pinus densiflora) is extensively cultivated in Japan, Korea, China, and Russia and is harvested for timber, pulpwood, garden, and paper markets. However, genetic information and molecular markers were very scarce for this species. In this study, over 51 million sequencing clean reads from P. densiflora mRNA were produced using Illumina paired-end sequencing technology. It yielded 83,913 unigenes with a mean length of 751 bp, of which 54,530 (64.98%) unigenes showed similarity to sequences in the NCBI database. Among which the best matches in the NCBI Nr database were Picea sitchensis (41.60%), Amborella trichopoda (9.83%), and Pinus taeda (4.15%). A total of 1953 putative microsatellites were identified in 1784 unigenes using MISA (MicroSAtellite) software, of which the tri-nucleotide repeats were most abundant (50.18%) and 629 EST-SSR (expressed sequence tag- simple sequence repeats) primer pairs were successfully designed. Among 20 EST-SSR primer pairs randomly chosen, 17 markers yielded amplification products of the expected size in P. densiflora. Our results will provide a valuable resource for gene-function analysis, germplasm identification, molecular marker-assisted breeding and resistance-related gene(s) mapping for pine for P. densiflora.

Tricholoma matsutake can absorb and accumulate trace elements directly from rock fragments in the shiro

Tricholoma matsutake, a highly valued delicacy in Japan and East Asia, is an ectomycorrhizal fungus typically found in a complex soil community of mycorrhizae, soil microbes, and host-tree roots referred to as the shiro in Japan. A curious characteristic of the shiro is an assortment of small rock fragments that have been implicated as a direct source of minerals and trace elements for the fungus. In this study, we measured the mineral content of 14 samples of shiro soil containing live matsutake mycelium and the extent to which the fungus can absorb minerals directly from the rock fragments. X-ray powder diffraction identified major phases of quartz, microcline, orthoclase, and albite in all shiro samples. PCR-denaturing gradient gel electrophoresis (DGGE) fingerprinting and direct sequencing confirmed the presence of T. matsutake on 32 of 33 rock fragments. Piloderma sp. co-occurred on 40% of fragments and was positively correlated with locations known to produce good mushroom crops. The ability of T. matsutake to absorb trace elements directly from rock fragments was examined in vitro on nutrient-agar plates supplemented with rock fragments from the shiro. In comparison to the mineral content of tissues grown on control media, the concentration of Al, Cu, Fe, Mn, P, and Zn increased from 1.1 to 106.4 times for both T. matsutake and Piloderma sp. Mineral content of dried sporocarps sampled from the study site partially reflected the results of the in vitro study. We discuss the implications of our results with respect to the natural development and artificial culture of this important fungus.

Tricholoma matsutake fruit bodies secrete hydrogen peroxide as a potent inhibitor of fungal growth

Tricholoma matsutake is an ectomycorrhizal fungus that dominates the microbial communities in the soil of pine and spruce forests. The mycorrhizas of this fungus have antimicrobial activity, although factors responsible for the antimicrobial activity have not been fully elucidated. The present study shows that fruit bodies of T. matsutake secreted hydrogen peroxide (H2O2), which was produced by pyranose oxidase, and that the H2O2 thus secreted strongly inhibited the growth of mycelia of the phytopathological fungus Rhizoctonia solani. These findings suggest that fruit bodies of T. matsutake have antifungal activity and that the pyranose oxidase plays an important role in the antifungal activity.

Soil propagule banks of ectomycorrhizal fungi along forest development stages after mining

Ectomycorrhizal fungal (EMF) propagules play an important role in seedling establishment following disturbance. However, little is known about how the EMF propagule community changes with forest development. In this study, EMF propagules were examined using seedling bioassays in rhizosphere soils collected from a recently closed Pb-Zn tailing (Taolin Pb-Zn tailing (TLT)), a Cu tailing (Dexing Cu No. 2 tailing (DXT)) that had undergone 21 years of restoration, and a mature Masson pine (Pinus massoniana) forest (DXC) outside the Cu mining areas. The corresponding EMF communities colonizing Masson pine at each site were also investigated for comparison. After 8 months of running bioassays, ectomycorrhizal colonization was poor for seedlings grown in TLT (9.0 % ± 14.9 %) and DXT soils (22.4 % ± 17.7 %), while DXC seedlings were well colonized (47.5 % ± 24.9 %). Internal transcribed spacer sequencing revealed that EMF species richness increased with forest development in both the propagule bank (TLT, 6; DXT, 7; DXC, 12) and in the field (TLT, 8; DXT, 14; DXC, 26), though richness was lower in propagule banks. Several lineages, such as Cenococcum, Rhizopogon, Inocybe, Suillus, and Atheliaceae, were frequently encountered in propagule communities, but species assemblages were different among the three sites. Canonical correspondence analysis revealed that several soil parameters, i.e., N, EC, Cu, Pb, Zn, etc., were responsible for the distribution of EMF in the field and bioassay seedlings. The highest overlap in EMF species composition between the propagule bank and the field community was observed at the recently closed tailing (Morisita-Horn similarity = 0.71 for TLT), whereas the lowest overlap occurred at the mature forest (0.26 for DXC). These results indicate that EMF propagules in soil are less frequent and diverse in early primary succession and become more frequent and diverse along forest development, due mainly to the accumulation of dormant spores of Rhizopogon spp. and sclerotia of Cenococcum spp. Thus, EMF propagule communities in soil may diverge from those root-colonizing EMF communities along a gradient of forest development.

Genetic variability and bottleneck detection of four Tricholoma matsutake populations from northeastern and southwestern China

The excessive commercial collection of matsutake mushrooms can lead to extreme reduction of population size, which may cause genetic bottleneck and decrease genetic diversity of Tricholoma matsutake. Here, six polymorphic microsatellite loci markers were used to examine the genetic diversity of four natural T. matsutake populations from two main producing regions of China. The minimum combinations of four loci were able to discriminate total 86 sampled individuals with distinctive multilocus genotypes. Our analysis of molecular variance (AMOVA) revealed that about 80% and 20% of the overall genetic variation were respectively partitioned within and among populations. The principal-coordinate analyses (PCA) distinguished the four tested populations into three genetic clusters, each of which was correlated with respective endemic host plants on a geographical basis. The AMOVA, PCA and pairwise population FST estimates consistently displayed the same genetic divergence patterns and spatial structure of T. matsutake mediated by host plants in China. The significant heterozygosity excesses demonstrated that a recent genetic bottleneck occurred in each population tested. The complementary M-ratio test indicated past genetic bottleneck events over longer periods. Only four individuals were identified as putative first generation migrants within northeastern China, which implies restricted interpopulation gene flow in T. matsutake. We discuss that the significant genetic differentiation among populations of T. matsutake is most likely a function of host adaptation, host specificity, genetic bottleneck, limited dispersal and habitat fragmentation.