Fingerprinting using extrolite profiles and physiological data shows sub-specific groupings of Penicillium crustosum strains

Fingerprinting of Penicillium crustosum strains was performed using different phenotypic characteristics. Seven strains of this extremely homogenous species were selected; of these, five originated from geographical locations characterized by low temperatures, and one from a location with a low water activity. Principal component analysis (PCA) was performed using micromorphological data, temperature- and water-dependent growth rates, and extrolite profiles obtained by HPLC analysis. The micromorphological data were less informative, while the growth-rate data were informative only if the strains investigated already showed slight adaptations to the selected external parameter. In contrast, PCA analyses of the extrolite data showed groupings of the strains according to their origins and known physiological differences. These groupings are in full agreement with the clustering obtained by previous amplified fragment length polymorphism (AFLP) study. We thus demonstrate here for the first time that combined qualitative and quantitative extrolite profiles can be used as a tool for phenotypic fingerprinting, to complement, or replace, molecular fingerprinting techniques.     

Local genes for local bacteria: Evidence of allopatry in the genomes of transatlantic Campylobacter populations

The genetic structure of bacterial populations can be related to geographical locations of isolation. In some species, there is a strong correlation between geographical distance and genetic distance, which can be caused by different evolutionary mechanisms. Patterns of ancient admixture in Helicobacter pylori can be reconstructed in concordance with past human migration, whereas in Mycobacterium tuberculosis it is the lack of recombination that causes allopatric clusters. In Campylobacter, analyses of genomic data and molecular typing have been successful in determining the reservoir host species, but not geographical origin. We investigated biogeographical variation in highly recombining genes to determine the extent of clustering between genomes from geographically distinct Campylobacter populations. Whole‐genome sequences from 294 Campylobacter isolates from North America and the UK were analysed. Isolates from within the same country shared more recently recombined DNA than isolates from different countries. Using 15 UK/American closely matched pairs of isolates that shared ancestors, we identify regions that have frequently and recently recombined to test their correlation with geographical origin. The seven genes that demonstrated the greatest clustering by geography were used in an attribution model to infer geographical origin which was tested using a further 383 UK clinical isolates to detect signatures of recent foreign travel. Patient records indicated that in 46 cases, travel abroad had occurred <2 weeks prior to sampling, and genomic analysis identified that 34 (74%) of these isolates were of a non‐UK origin. Identification of biogeographical markers in Campylobacter genomes will contribute to improved source attribution of clinical Campylobacter infection and inform intervention strategies to reduce campylobacteriosis.     

AFLP based assessment of genetic relationships among shiitake (<Emphasis Type="Italic">Lentinula</Emphasis> ssp.) mushrooms

Despite the economical importance of shiitake (Lentinula ssp.) mushrooms, until the present date little information exists on cultivated and wild species in correlation with geographic origin applying molecular techniques. Use of a high resolution molecular tool like AFLP for assessing genetic similarity and geographical diversity would be an important step towards understanding of different Lentinula species. Thirteen wild and 17 cultivated accessions of 3 Lentinula species were analysed with 64 EcoRI–MseI primer combinations and finally 32 reproducible and polymorphic primer combinations were considered for the analysis. A total of 816 informative AFLP markers were generated and scored as binary data. These data were analysed using various method packages for cluster analysis, genetic diversity and genetic differentiation. Percentage polymorphism was high (62.99%) among the species studied. Different clustering analysis segregated the wild and the cultivated species into two major branches, with the wild samples being further grouped according to their geographic location. Overall polymorphisms among cultivated strains in the USA were higher than that of the cultivated strains in Japan (58.9%).     

Phylogeographic relationships in the polypore fungus Pycnoporus inferred from molecular data

The genus Pycnoporus forms a group of four species known especially for producing high redox potential laccases suitable for white biotechnology. A sample of 36 Pycnoporus strains originating from different geographical areas was studied to seek informative molecular markers for the typing of new strains in laboratory culture conditions and to analyse the phylogeographic relationships in this cosmopolitan group. ITS1-5.8S-ITS2 ribosomal DNA and partial regions of β-tubulin and laccase lac3-1 gene were sequenced. Phylogenetic trees inferred from these sequences clearly differentiated the group of Pycnoporus cinnabarinus strains from the group of Pycnoporus puniceus strains into strongly supported clades (100% bootstrap value). Molecular clustering based on lac 3-1 sequences enabled the distribution of Pycnoporus sanguineus and Pycnoporus coccineus through four distinct, well supported clades and sub-clades. A neotropical sub-clade, grouping the P. sanguineus strains from French Guiana and Venezuela, corresponded to P. sanguineus sensu stricto. A paleotropical sub-clade, clustering the strains from Madagascar, Vietnam and New Caledonia, was defined as Pycnoporus cf. sanguineus. The Australian clade corresponded to P. coccineus sensu stricto. The Eastern Asian region clade, clustering the strains from China and Japan, formed a P. coccineus-like group. Laccase gene (lac 3-1) analysis within the Pycnoporus species can highlight enzyme functional diversity associated with biogeographical origin.     

Diversity of Physiological and Biochemical Characters of Microdochium Fungi

The biological characterization of Microdochium majus, M. nivale, and M. seminicola strains with wide geographical origins showed the diversity of their pathogenic properties and metabolite compounds, allowing them to exist in their habitats. Significant differences in the ability of Microdochium fungi to cause lesions on wheat and oat leaves were found. The intensity of symptoms depended on the species and substrate origin of the strains. On average M. seminicola strains were able to cause less leaf necrosis than M. majus and M. nivale. The volatile organic compound (VOC) profile of Microdochium fungi included 29 putative fungal metabolites. The spectrum of the identified VOCs in M. seminicola strains was much richer than that in M. majus and M. nivale strains. In addition, the strains of M. seminicola emitted at least six sesquiterpenes. Mycotoxin analysis by HPLC/MS/MS revealed that the analyzed Microdochium strains did not produce any toxic metabolites typically produced by filamentous fungi.     

Geographical markers for <Emphasis Type="Italic">Saccharomyces cerevisiae</Emphasis> strains with similar technological origins domesticated for rice-based ethnic fermented beverages production in North East India

Autochthonous strains of Saccharomyces cerevisiae from traditional starters used for the production of rice-based ethnic fermented beverage in North East India were examined for their genetic polymorphism using mitochondrial DNA-RFLP and electrophoretic karyotyping. Mitochondrial DNA-RFLP analysis of S. cerevisiae strains with similar technological origins from hamei starter of Manipur and marcha starter of Sikkim revealed widely separated clusters based on their geographical origin. Electrophoretic karyotyping showed high polymorphism amongst the hamei strains within similar mitochondrial DNA-RFLP cluster and one unique karyotype of marcha strain was widely distributed in the Sikkim-Himalayan region. We conceptualized the possibility of separate domestication events for hamei strains in Manipur (located in the Indo-Burma biodiversity hotspot) and marcha strains in Sikkim (located in Himalayan biodiversity hotspot), as a consequence of less homogeneity in the genomic structure between these two groups, their clear separation being based on geographical origin, but not on technological origin and low strain level diversity within each group. The molecular markers developed based on HinfI-mtDNA-RFLP profile and the chromosomal doublets in chromosome VIII position of Sikkim-Himalayan strains could be effectively used as geographical markers for authenticating the above starter strains and differentiating them from other commercial strains.     

Weighted rank aggregation of cluster validation measures: a Monte Carlo cross-entropy approach

MOTIVATION: Biologists often employ clustering techniques in the explorative phase of microarray data analysis to discover relevant biological groupings. Given the availability of numerous clustering algorithms in the machine-learning literature, an user might want to select one that performs the best for his/her data set or application. While various validation measures have been proposed over the years to judge the quality of clusters produced by a given clustering algorithm including their biological relevance, unfortunately, a given clustering algorithm can perform poorly under one validation measure while outperforming many other algorithms under another validation measure. A manual synthesis of results from multiple validation measures is nearly impossible in practice, especially, when a large number of clustering algorithms are to be compared using several measures. An automated and objective way of reconciling the rankings is needed. RESULTS: Using a Monte Carlo cross-entropy algorithm, we successfully combine the ranks of a set of clustering algorithms under consideration via a weighted aggregation that optimizes a distance criterion. The proposed weighted rank aggregation allows for a far more objective and automated assessment of clustering results than a simple visual inspection. We illustrate our procedure using one simulated as well as three real gene expression data sets from various platforms where we rank a total of eleven clustering algorithms using a combined examination of 10 different validation measures. The aggregate rankings were found for a given number of clusters k and also for an entire range of k. AVAILABILITY: R code for all validation measures and rank aggregation is available from the authors upon request. SUPPLEMENTARY INFORMATION: Supplementary information are available at http://www.somnathdatta.org/Supp/RankCluster/supp.htm.     

Degradation and enzymatic activities of three Paecilomyces inflatus strains grown on diverse lignocellulosic substrates

This paper describes for the first time in detail the lignocellulose degradation system in Paecilomyces inflatus. The fungal genus Paecilomyces contributes the carbon turnover from lignin and carbohydrate plant residues, particularly in compost and soil environment, where basidiomycetes appear very seldom. We studied three different strains of P. inflatus, obtained from different ecophysiological and geographical origin. Various cultivation conditions were employed, and the chemical analysis of decayed straw, compost, birch and spruce wood chips indicated variable responses. Endoglucanase, xylanase and laccase were assayed. All strains of P. inflatus, regardless of their origin, altered the ambient pH in a similar manner in all investigated substrates, suggesting that all P. inflatus isolates may share the common regulatory system to control their environmental pH. The variability among strains of P. inflatus in their ability to remove lignocellulose components often was related to the nature of the substrate and the production of specific enzymes although it was not strictly correlated. This may implicate that other enzymes and/or even other parameters needed for lignocellulosics degradation in P. inflatus should be evaluated. Indications for specific adaptation strategies that may operate in P. inflatus were found.     

Geographical range and host breadth of Sebacina orchid mycorrhizal fungi associating with Caladenia in south‐western Australia

Specialized mycorrhizal interactions have the potential to limit the geographical range of plant species and contribute to reproductive isolation. We investigated these predictions in Caladenia (Orchidaceae) from south‐western Australia, a group known to have specialized mycorrhizal associations with the genus Sebacina s.l. Sequencing of fungal isolates from 47 of the 136 species of Western Australian Caladenia was undertaken to resolve the geographical range and habitat preferences of mycorrhizal fungal operational taxonomic units (OTUs) and their host breadth in Caladenia. Eight different fungal OTUs were used by Caladenia, with the more frequently detected OTUs occurring in a wide range of habitats and geographical regions. Given the comparatively narrow geographical ranges of most Western Australian Caladenia taxa, this suggests that the geographical ranges of fungal OTUs are unlikely to limit the geographical range of Caladenia spp. Extensive sharing of fungal OTUs between closely related orchid species was detected, suggesting that in the main there is little potential for mycorrhizal fungi to contribute to reproductive isolation between Caladenia spp. Our data mostly support previous work suggesting high mycorrhizal specificity in Caladenia, but this may not be the case in all subgenera, highlighting that Caladenia may offer powerful opportunities for investigating the evolution of specialized mycorrhizal associations.     

Species concept and morphological differentiation of strains traditionally assigned to Micrasterias truncata

The morphological and molecular differentiation of the Micrasterias truncata (Corda) ex Bréb species complex was investigated. In total, 17 strains traditionally assigned to M. truncata were isolated from different European localities (Czech Republic, southwest France, Ireland), and obtained from public culture collections. In addition, strains of the morphologically similar species, M. decemdentata (Nägeli) W. Archer and M. zeylanica F. E. Fritsch, were also included. Molecular phylogenetic analysis based on trnG^ucc intron sequences revealed five well supported clades. Two Australian strains assigned to M. truncata var. pusilla G. S. West formed a lineage sister to M. zeylanica. This was evident from a concatenated phylogeny based on small subunit rDNA and trnG^ucc intron sequences. The isolated position of these strains was also illustrated by parallel landmark‐based geometric morphometric analysis of cell shapes. The strains NIES 783 and NIES 784 probably represent a separate species. Particular analysis, including additional strains, is needed to resolve the relationship inside this lineage. The second phylogenetic lineage, containing two strains of M. truncata var. semiradiata (Kützing) Wolle, was also different from other strains on the basis of morphometric data. We suggest recognizing this variety as a separate species, Micrasterias semiradiata L.A. Brébisson ex F. T. Kützing. The remaining three clades formed a firmly supported group of the ‘core’M. truncata recognized by both molecular markers. However, neither any morphological, morphometric, nor geographical pattern was detected among members of these three clades. This pattern could be caused by a relatively recent origin of these lineages that may represent a sympatric, truly cryptic species. Strains attributable to traditional morphologically defined variety M. truncata var. neodamensis were nested within the ‘core’M. truncata.     

An Integrated Study of the Species Problem in the Euplotes crassus-minuta-vannus Group1

ABSTRACT. In an attempt to solve the ambiguity in the taxonomy of the Euplotes crassus, minuta, and vannus group, 19 strains were tested for mating interactions, electrophoresed for isozymic variations, and analyzed by multivariate morphometrics of the conventional diagnostic traits. The overall results supported the validity of the three named species. Inter-specific mating occurred only in a few crassus x vannus strain combinations and was usually inviable. Isozymic variations, in particular of amylases, malic enzyme, and malic dehydrogenase, were very restricted within conspecific strains and were great between non-conspecifics. The species ascertainment of the strains was possible on the basis of clustering and principal component analyses of morphological measures.     

Characterization of Pseudomonas syringae pv. tomato by Numerical Analysis of Phenotypic Features and Total Soluble Proteins11)

Abstract The homogeneity of South African and other strains of Pseudomonas syringae pv. tomato was determined by numerical analysis of differential phenotypic features and computer-assisted comparison of gel electropherograms of soluble proteins. Two closely-related groups, that could only be separated by their reaction in litmus milk, were distinguished in a phenotypic dendrogram. Three non-South African reference strains fell outside these groups, indicating the possible existence of more groups, worldwide. No clear-cut correlation was found between clustering of strains and their geographical origin. Forty-seven strains examined had similar protein patterns, reflecting their close genetic resemblance. All strains were pathogenic on tomatoplants.     

Competitiveness of Diverse Methylobacterium Strains in the Phyllosphere of Arabidopsis thaliana and Identification of Representative Models, Including M. extorquens PA1

Facultative methylotrophic bacteria of the genus Methylobacterium are consistently found in association with plants, particularly in the phyllosphere. To gain a better understanding of the mechanisms underlying the dispersal and occurrence of Methylobacterium on plants, diverse strains were isolated, identified, and studied with regard to their competitiveness on the model plant Arabidopsis thaliana. As a basis for this study a comprehensive collection of Methylobacterium isolates was established. Isolates were obtained from five different naturally grown A. thaliana populations and diverse other plant genera at these and further sites. They were classified using automated ribosomal internal spacer analysis (ARISA) and a representative subset was identified based on 16S rRNA gene sequence analysis. A comparison of their ARISA patterns with those generated based on a cultivation-independent approach from the same sampling material confirmed that the isolates were abundant colonizers of the studied plants. In competition experiments, colonization efficiency of the strains was found to be linked to phylogeny, rather than to the geographical origin or plant genus from which they were isolated. The most competitive colonizers were related to the species Methylobacterium tardum and Methylobacterium extorquens. Higher cell numbers were observed in the phyllosphere of A. thaliana when a mixture of different strains was applied relative to inoculation with only one strain, suggesting partial niche heterogeneity. Based on the results of the competition experiments, representative strains with different colonization efficiencies were selected, which will serve as models in future studies aiming at a better understanding of plant colonization by this bacterial genus. Among them is the meanwhile genome-sequenced strain M. extorquens PA1, which represents a competitive species of plant colonizers with a broad dispersal. This strain was characterized in more detail including physiological, morphological, and chemotaxonomical properties.     

Quantitative trait, genetic, environmental, and geographical distances among populations of the C4 grass Trachypogon plumosus in Neotropical savannas

Venezuelan savannas are exposed to land‐use changes and biological invasions which compromise their persistence and function. The native C₄ grass Trachypogon plumosus is the most important component of the savannas under diverse combinations of climate and soils, suggesting substantial interpopulation variation. We examined quantitative traits and isozyme variation of nine populations of this grass and related these estimates to geographical and environmental features of sampled locations. Isozyme diversity estimates were based on 10 polymorphic enzyme systems whereas 21 quantitative traits, from field and controlled growth conditions, were evaluated. Distance matrices for quantitative traits, isozyme, geographical and environmental data were subjected to clustering analysis. Correspondence between quantitative trait distance and genetic distance, and their association to geographical and environmental distances were analysed with Mantel tests. All quantitative traits differed significantly among populations. The average Q_ST calculated for eight quantitative traits measured in the greenhouse was 0.157. Isozyme diversity differed significantly among populations. About 28% of total isozyme variation occurred among populations. Significant positive associations were detected between environmental, quantitative field traits, and geographical distance as well as between the later and genetic distances. Genetic distances did not correspond significantly with quantitative traits nor did environmental distances. Ecologically meaningful associations were detected between field quantitative traits, environmental, and geographical data using cluster analysis. Our results support the hypothesis that processes of the neutral type are mainly responsible for the variation patterns observed in T. plumosus populations in Venezuelan savannas. Variation observed for quantitative traits among populations seems to be due to the effect of environmental conditions on phenotypically plastic traits, and not the result of directional selection favouring different phenotypes in different populations.     

Molecular identification and phylogenetic analysis of fungal pathogens isolated from diseased fish in Xinjiang,China

The outbreaks of fungal diseases in cultured fish have been severe in recent years, which is harmful to the healthy and sustainable development of fish farming. In this study, an investigation was conducted for significant fungal infections of 12 species of fish in four regions in Xinjiang, China, to understand the distribution of local fish fungal pathogens. Twenty-six fungal strains with pathogenicity were isolated, and the challenge experiment showed that eight strains from Changji area had high infection rate to fish eggs. Based on internal transcribed spacer sequence data and molecular analysis, the 26 strains were classified into nine different species of six fungal genera. Phylogenetic analysis showed that all strains were divided into two clades, namely Cluster 1 (contains only the genus Mucor) and Cluster 2 (consists of five small branches), and the distribution of strains from the same region was scattered in two clusters. There is no strict host selectivity for these fungi to infect fish. Mucor sp. are the main fungal pathogen of fish in these four regions, whereas Hypophthalmichthys molitrix and Carassius auratus are two types of fish that were susceptible to pathogen. In addition, the environmental adaptability experiments showed that eight highly pathogenic strains have different adaptability to the environment, and their optimum temperature and pH were 25°C and 7.0, respectively, whereas the concentration of NaCl was negatively correlated with the growth of strains. Therefore, these results indicated that the coinfection of multiple fungal pathogens in a culture region should be considered in the future study.     

Outbreaks of Mucorales and the Species Involved

The order Mucorales is an ancient group of fungi classified in the subphylum Mucoromycotina. Mucorales are mainly fast-growing saprotrophs that belong to the first colonizers of diverse organic materials and represent a permanent part of the human environment. Several species are able to cause human infections (mucormycoses) predominantly in patients with impaired immune system, diabetes, or deep trauma. In this review, we compiled 32 reports on community- and hospital-acquired outbreaks caused by Mucorales. The most common source of mucoralean outbreaks was contaminated medical devices that are responsible for 40.7% of the outbreaks followed by contaminated air (31.3%), traumatic inoculation of soil or foreign bodies (9.4%), and the contact (6.2%) or the ingestion (6.2%) of contaminated plant material. The most prevalent species were Rhizopus arrhizus and R. microsporus causing 57% of the outbreaks. The genus Rhizomucor was dominating in outbreaks related to contaminated air while outbreaks of Lichtheimia species and Mucor circinelloides were transmitted by direct contact. Outbreaks with the involvement of several species are reported. Subtyping of strains revealed clonality in two outbreaks and no close relation in two other outbreaks. Based on the existing data, outbreaks of Mucorales can be caused by heterogeneous sources consisting of different strains or different species. Person-to-person transmission cannot be excluded because Mucorales can sporulate on wounds. For a better understanding and prevention of outbreaks, we need to increase our knowledge on the physiology, ecology, and population structure of outbreak causing species and more subtyping data.

     

An ecological classification of European Drosophila species

Summary The associations shown between species of Drosophila collected in three European countries are analysed using a clustering method. The resulting dendrograms are combined to give a plan of associations shown by all three surveys. These general groupings are interpreted in the light of what is known about Drosophila breeding sites.One ecological group, the fungal breeding species are examined in detail and their pattern of geographical associations investigated. The three most abundant species in collections, D. transversa, D. phalerata and D. cameraria appear to replace one another in a north-south direction in western Europe. It is suggested that ecologically marginal areas may be defined using the frequency of a species within its ecological group.     

Pyrolysis mass spectrometry characterisation and numerical taxonomy ofAeromonas spp.

Reference strains (2) and 29 isolates ofAeromonas spp. from clinical material and environmental specimens were characterised in traditional biochemical tests, and in pyrolysis mass spectrometry, which gives data reflecting whole-cell composition. Numerical taxonomic analyses of the data sets were compared with conventional identification at species level, and pathogenic potential, as inferred from the origin of the isolates. Clustering with conventional test reaction patterns showed, for each of the species represented, a clearly defined core group of typical isolates, surrounded by a halo of aberrant strains. One further cluster comprised strains intermediate betweenA. caviae andA. hydrophila, and one strain was grossly atypical in both analyses. Clustering from pyrolysis data corresponded less well with species identification. Broadly, the biochemical division between core and halo strains was supported in pyrolysis forA. caviae andA. sobria, but the main group ofA. hydrophila in pyrolysis comprised strains clustering in the core and halo groups of this species, and three strains intermediate betweenA. hydrophila andA. caviae in biochemical tests. Two further pyrolysis clusters comprised core and halo strains ofA. hydrophila. However, pyrolysis clustering correlated well with inferred pathogenicity, showing four clusters of probable pathogens, six clusters of probable nonpathogens, and one two member cluster of doubtful status. Most strains that clustered in the species haloes, or in species-intermediate groups in biochemical tests, were non-human isolates, or were isolated in the absence of symptomatic infection. The correlation of inferred pathogenicity with biochemical clustering was poorer than that with pyrolysis clustering.Abbreviations CTRP conventional test reaction pattern - PyMS pyrolysis mass spectrometry     

Polymorphism of Paramecium pentaurelia (Ciliophora, Oligohymenophorea) strains revealed by rDNA and mtDNA sequences

Paramecium pentaurelia is one of 15 known sibling species of the Paramecium aurelia complex. It is recognized as a species showing no intra-specific differentiation on the basis of molecular fingerprint analyses, whereas the majority of other species are polymorphic. This study aimed at assessing genetic polymorphism within P. pentaurelia including new strains recently found in Poland (originating from two water bodies, different years, seasons, and clones of one strain) as well as strains collected from distant habitats (USA, Europe, Asia), and strains representing other species of the complex. We compared two DNA fragments: partial sequences (349 bp) of the LSU rDNA and partial sequences (618 bp) of cytochrome B gene. A correlation between the geographical origin of the strains and the genetic characteristics of their genotypes was not observed. Different genotypes were found in Kraków in two types of water bodies (Opatkowice—natural pond; Jordan's Park—artificial pond). Haplotype diversity within a single water body was not recorded. Likewise, seasonal haplotype differences between the strains within the artificial water body, as well as differences between clones originating from one strain, were not detected. The clustering of some strains belonging to different species was observed in the phylogenies.     

Diversity and composition of ectomycorrhizal community on seedling roots: the role of host preference and soil origin

As the main source of inocula, ectomycorrhizal (ECM) fungal propagules are critical for root colonization and seedling survival in deforested areas. It is essential to know factors that may affect the diversity and composition of ECM fungal community on roots of seedlings planted in deforest areas during reforestation. We quantitatively evaluated the effect of host plant and soil origin on ECM fungal propagule community structure established on roots of Castanopsis fargesii, Lithocarpus harlandii, Pinus armandii, and Pinus massoniana growing in soils from local natural forests and from sites deforested by clear-cut logging in the 1950s and 1960s. ECM root tips were sampled in April, July, and October of 2006, and ECM fungal communities were determined using ECM root morphotyping, internal transcribed spacer (ITS)-RFLP, and ITS sequencing. A total of 36 ECM fungal species were observed in our study, and species richness varied with host species and soil origin. Decreased colonization rates were found in all host species except for L. harlandii, and reduced species richness was found in all host species except for P. armandii in soil from the deforested site, which implied the great changes in ECM fungal community composition. Our results showed that 33.3% variance in ECM fungal community composition could be explained by host plant species and 4.6% by soil origin. Results of indicator species analysis demonstrated that 14 out of 19 common ECM fungal species showed significant preference to host plant species, suggesting that the host preference of ECM fungi was one of the most important mechanisms in structuring ECM fungal community. Accordingly, the host plant species should be taken into account in the reforestation of deforested areas due to the strong and commonly existed host preference of ECM fungi.