Root-associated Fungi Research Articles

<i>Pterostylis nutans</i> (Orchidaceae) has a specific association with two <i>Ceratobasidium</i> root-associated fungi across its range in eastern Australia

In this study, we have identified the root-associated fungi of a common species of terrestrial orchid across its range in eastern Australia. We have amplified and cloned fungal ITS DNA extracted from roots of 15 Pterostylis nutans R. Br. plants from six separate geographic localities. Sequencing and GenBank comparison demonstrated two species of Ceratobasidium fungi as the main fungal partners of the orchid. Uncommon fungal associates included homobasidiomycete species such as a Gymnomyces sp. and a Tricholoma sp., Leptodontidium orchidicola, and an unidentified soil fungus. These results demonstrate that specificity for fungal partners occurs in P. nutans and reinforces the idea that conservation measures for endangered Australian orchids must include ex situ perpetuation of fungal symbionts as well as plant material.

Phylogenetic and structural analyses of the mating-type loci inClavicipitaceae

Entomopathogens and other econutritional fungi belonging to Clavicipitaceae were phylogenetically analyzed on the basis of the 18S rRNA gene and mating-type genes (MAT1-1-1 and MAT1-2-1). The phylogenies of the mating-type genes yielded better resolutions than that of 18S rRNA gene. Entomopathogens (Cordyceps bassiana, Cordyceps brongniartii, Cordyceps militaris, Cordyceps sinclairii, Cordyceps takaomontana, Isaria cateniannulata, Isaria farinosa, Isaria fumosorosea, Isaria javanica, Lecanicillium muscarium and Torrubiella flava) were considered as a phylogenetically defined group, and were closely related to mycopathogens (Lecanicillium psalliotae and Verticillium fungicola). They located at more descendant positions in the mating-type trees than other fungi, and lacked the mating-type gene MAT1-1-3. The deletion of MAT1-1-3 was supposed to have occurred once in Clavicipitaceae, and a good indication for the evolution of Clavicipitaceae. Other entomopathogens (Cordyceps cylindrica, Cordyceps subsessilis, Metarhizium anisopliae and Nomuraea rileyi) and pathogens of plants, nematodes and slime molds, were relatively related to each other, and possessed MAT1-1-3, but were supposed to be heterogeneous. Root-associated fungi did not form any clade with other species.

High diversity of fungi recovered from the roots of mature tanoak (Lithocarpus densiflorus) in northern California

We collected mature tanoak ( Lithocarpus densiflorus (Hook. & Arn.) Rehder) roots from five stands to characterize the relative abundance and taxonomic richness of root-associated fungi. Fungi were identified using polymerase chain reaction (PCR), cloning, and sequencing of internal transcribed spacer (ITS) and 28S rDNA. A total of 382 cloned PCR inserts were successfully sequenced and then classified into 119 taxa. Of these taxa, 82 were basidiomycetes, 33 were ascomycetes, and 4 were zygomycetes. Thirty-one of the ascomycete sequences were identified as Cenococcum geophilum Fr. with overall richness of 22 ITS types. Other ascomycetes that form mycorrhizal associations were identified including Wilcoxina and Tuber as well as endophytes such as Lachnum , Cadophora , Phialophora , and Phialocephela . The most abundant mycorrhizal groups were Russulaceae ( Lactarius , Macowanites , Russula ) and species in the Thelephorales ( Bankera , Boletopsis , Hydnellum , Tomentella ). Our study demonstrates that tanoak supports a high diversity of ectomycorrhizal fungi with comparable species richness to that observed in Quercus root communities.

Chitinolytic activities of ericoid mycorrhizal and other root-associated fungi from Epacris pulchella ( Ericaceae)

Ericoid mycorrhizal endophytes and other root-associated fungi from Epacris pulchella (Ericaceae) in an eastern Australian sclerophyll forest, along with Hymenoscyphus ericae, were tested for their abilities to produce extracellular chitinolytic activities during growth in axenic culture. Two root-associated fungi produced activities that were active against only a monomeric 4-methylumbelliferyl (4-MU) glycoside of N-acetylglucosamine, suggesting exo-acting beta-N-acetylhexosaminidase (EC 3.2.1.52) activity. All ericoid mycorrhizal fungi and two root-associated fungi produced activities against dimeric and trimeric 4-MU glycosides of N-acetylglucosamine, suggesting production of chitobiosidase and endo-acting chitinase (EC 3.2.1.14) respectively in addition to beta-N-acetylhexosaminidase. Specific activities for all ericoid mycorrhizal fungi, including H. ericae, were of the same order of magnitude, suggesting that their chitinolytic potential is broadly similar. Chitinase activities were only produced by an ericoid mycorrhizal fungus when chitin was included in the medium, however, no activity was produced if glucose was also present in the medium.

Morphological and molecular typing of the below-ground fungal community in a natural Tuber magnatum truffle-ground

The aims of the work were to elucidate the distribution of the ectomycorrhizal fungus Tuber magnatum Pico during its symbiotic stage, and to identify the root-associated fungi in a natural truffle-ground located in North Italy. Ectomycorrhizal root tips were harvested in the truffle ground, sorted in morphotypes and analyzed by ITS. Morphological and molecular analyses revealed that (i) T. magnatum mycorrhizae were rare and independent on the fruitbody productions and (ii) the dominant fungal species belonged to Thelephoraceae, followed by Tuberaceae and Sebacinaceae.

Seeking the elusive function of the root-colonising dark septate endophytic fungi

A comparison of published estimates of mycorrhizal and dark septate endophyte (DSE) colonisation from various ecosystems suggests that DSE may be as abundant as mycorrhizal fungi as judged by the proportion of host plants colonised in mixed plant communities, or by the extent of colonisation in sampled root systems. While many strides have been made in understanding the ecological significance of the mycorrhizal fungi, our knowledge about the role of DSE fungi is in its infancy. In order to provide a framework of testable hypotheses, we review and discuss the most likely functions of this poorly understood group of root-associated fungi. We propose that, like mycorrhizal symbioses, DSE-plant symbioses should be considered multifunctional and not limited to nutrient acquisition and resultant positive host growth responses. Admittedly, many mycorrhizal and endophyte functions, (e.g. stress tolerance, pathogen or herbivore deterrence) are likely to be mediated by improved nutritional status and increased fitness of the host. Accordingly, it is pivotal to establish whether or not the DSE fungi are involved in host nutrient acquisition, either from inorganic and readily soluble sources, or from organic and recalcitrant sources. Facilitation by DSE of the use of organic nitrogen, phosphorus and sulphur sources by plants is a topic that warrants further attention and research. Even in the absence of a clear nutrient uptake function, the extensive DSE colonisation that occurs is likely to pre-emptively or competitively deter pathogens by minimising the carbon available in host rhizosphere environment. The DSEs' high melanin levels and their potential production of secondary metabolites toxic or inhibitory to herbivores are also likely to be factors influencing host performance. Finally, the broad host ranges speculated for most DSE fungi thus far suggest that they are candidates for controlling plant community dynamics via differential host responses to colonisation. We emphasise the need for simple experiments that allow unravelling of the basic biological functions of DSE fungi when they colonise their hosts.

Meliniomyces, a new anamorph genus for root-associated fungi with phylogenetic affinities to Rhizoscyphus ericae (≡ Hymenoscyphus ericae), Leotiomycetes

Abstract Sterile fungi isolated from surface-sterilized roots of the Ericaceae, and hypothesized to be conspecific based primarily on restriction fragment length polymorphisms, were provisionally named as Variable White Taxon (VWT). In preliminary resynthesis trials with Vaccinium myrtilloides or V. vitis-idaea, isolates did not form typical ericoid mycorrhizas. Additional isolates obtained from roots of the Orchidaceae, Pinaceae, Betulaceae and Salicaceae, and given informal names such as Sterile white 1 (SW1), were thought to represent the same taxon based on cultural similarities. To evaluate conspecificity and infer phylogenetic affinities, partial nuclear ribosomal DNA sequences were determined. Parsimony analyses supported a species level distinction for VWT/SW1 and indicated that the fungus is placed within the species complex referred to as the “ Hymenoscyphus ericae aggregate” which includes H. ericae ( Leotiomycetes ), many unnamed taxa and Cadophora finlandica. The new genus and species Meliniomyces variabilis is proposed to accommodate this root-associated fungus to facilitate discussion and information retrieval, and to provide a foundation for additional experimental work. Although isolates are sterile in culture, they can be identified by morphological characters in conjunction with ribosomal internal transcribed spacer (ITS) sequence data. The mycorrhizal status of M. variabilis is not yet clear. In prior published results, strains demonstrated no or some colonization with ericoid and ectomycorrhizal hosts but did not form true ectomycorrhizas. ITS analyses indicated that the “ H. ericae aggregate” includes several other well-supported clades putatively named as Meliniomyces species. Representative strains were examined morphologically for two of these species, described as M. vraolstadiae and M. bicolor. Both include ectomycorrhizal mycobionts of the “ Piceirhiza bicolorata ” morphotype. Rhizoscyphus ericae is accepted as the appropriate name for H. ericae. Taxonomic novelties: Meliniomyces Hambleton & Sigler anam. gen. nov., Meliniomyces variabilis Hambleton & Sigler sp. nov., Meliniomyces bicolor Hambleton & Sigler sp. nov., Meliniomyces vraolstadiae Hambleton & Sigler sp. nov.

Distribution of ericoid mycorrhizal endophytes and root-associated fungi in neighbouring Ericaceae plants in the field

Three hundred and twenty-seven fungal endophyte isolates were obtained from hair roots of neighbouring Woollsia pungens Cav. (Muell.) and Leucopogon parviflorus (Andr.) Lindl. (both Ericaceae) plants at an Australian dry sclerophyll forest site and mapped according to the root segments from which they were obtained. Restriction fragment length polymorphism (RFLP) analysis of the rDNA internal transcribed spacer (ITS) region indicated that the isolate assemblage comprised 21 RFLP-types (= putative taxa), five of which were shown in gnotobiotic culture experiments to be ericoid mycorrhizal endophytes. While two mycorrhizal RFLP-types were exclusive to either W. pungens or L. parviflorus, RFLP-type VI was isolated from both hosts. This putative taxon had strong ITS sequence identity with Helotiales ericoid mycorrhizal ascomycetes, comprised ca. 75% of all isolates from each plant and was spatially widespread in both root systems. Inter-simple sequence repeat PCR analysis indicated that two and four genotypes of RFLP-type VI were present in the W. pungens and L. parviflorus root systems respectively, however single genotypes appeared to dominate each root system. One genotype was present in both root systems. The data suggest that assemblages of ericoid mycorrhizal fungi from hair roots of individual Ericaceae plants in dry sclerophyll forest habitats are characterised by relatively low genetic diversity.

Estimation of the biomass of fine roots and mycorrhizal fungi: a case study in a Japanese red pine (Pinus densiflora) stand

As part of a study on soil carbon flow in forest ecosystems, the biomass of fine roots (<2.0mm in diameter) and root-associated fungi, including ectomycorrhizal fungi, were estimated in the summer season in 1998 at a Pinus densiflora (Japanese red pine) stand in western Japan. Fine roots of pine were classified into three categories: class I roots (0.5–2.0mm in diameter), long class II roots (long roots with diameter <0.5mm; IIL), and short class II roots (short roots with diameter <0.5mm; IIS). Total biomass of fine roots (I + IIL + IIS) at this stand was estimated to be 91.0gm–2, about 23% of which was class II roots (IIL + IIS). Ergosterol, which is a component of fungal membranes, was analyzed to estimate the biomass of root-associated fungi in roots. In the upper soil layers (from the surface to 13.4cm in depth), ergosterol contents in the class I, IIL and IIS roots were in the ranges 43.1–82.2, 126.1–196.3 and 271.2–321.0μgg–1 root DW, respectively. The ergosterol content was converted to fungal biomass using the median (minimum–maximum) value of ergosterol concentration reported for ectomycorrhizal fungi. Root-associated fungal biomass in this stand was estimated to be 2.0 (0.5–9.6) gm–2. The data suggest the biomass of ectomycorrhizal fungi in the P. densiflora stand is small compared with that in other forest ecosystems.

Mycorrhiza and root-associated fungi in Spitsbergen

Roots of 76 plant species collected in West Spitsbergen (Svalbard), in the middle-northern Arctic zone, were examined for mycorrhiza and root-associated fungi. Dryas octopetala, Pedicularis dasyantha and Salix polaris were ectomycorrhizal and Cassiope tetragona and Empetrum hermaphroditum ericoid mycorrhizal. Pedicularis dasyantha was only slightly infected. Structures resembling vesicular-arbuscular mycorrhizal (VAM) fungi were not found in the roots, and soil samples screened for VAM fungi contained only one spore. Root endophytic fungi commonly occurred in Spits-bergen, but only Olpidium brassicae, Pleospora herbarum, Papulaspora, Microdochium bolleyi and Rhizoctonia solani were identified with reasonable certainty. A sterile endophytic dark-septate fungus (DSF) was in 39.5% of the flowering-plant species examined, especially in the Brassicaceae, Caryophyllaceae, Saxifragaceae and Poaceae. DSF were categorized into four slightly overlapping groups. Sterile endophytic hyaline septate fungi were rare. In the literature it is suggested that at least some of the DSF species or the hyaline septate fungi are functionally mutualistic rather than saprophytic or pathogenic. The literature on ectomycorrhizal fungi and plants in Spitsbergen is reviewed, including about 50 species, mainly of the genera Cortinarius, Hebeloma, Inocybe, Laccaria, Lactarius and Russula. These are symbiotic with the above-mentioned ectomycorrhizal plants. Four further ectomycorrhizal plants (Betula nana, Salix spp.) are very rare in the area.

Fungi Associated with the Roots of Red Mangrove, Rhizophora mangle

SUMMARYThe microbial communities of root-free soil, the rhizosphere and rhizoplane of red mangrove seedlings, Rhizophora mangle L., growing in Heeia swamp, Oahu, Hawaii, were studied by dilution plating, Harley and Waid's repeated washing technique, and a root maceration method. In addition, macrofungi associated with R. mangle roots were observed directly. By this combination of methods eight new records for fungi associated with mangroves were established. The isolation methods selected for isolating root-associated fungi are discussed. Results are evaluated within the limits of the methods employed.There was a pronounced rhizosphere effect with greater numbers of bacteria, actinomycetes, and fungi occurring at all salinity levels in the rhizosphere soil than in the root-free soil at corresponding salinity levels. Primarily the microfungi isolated from the rhizoplane were known root-surface or root-tissue fungi. In the rhizosphere community Fungi Imperfecti contributed 87.9% of the species isolated. Phycomycetes and Ascomycetes comprised the balance. No Phycomycetes were recovered from either the rhizoplane or macerated roots. This low recovery of Phycomycetes in mangrove habitats is in correspondence with all reports except one. Ascomycetes were isolated from the rhizosphere, the rhizoplane, live roots above the tidal line, and dead roots below the tidal line. Basidiomycetes and Myxomycetes were found only on live prop roots above the tidal line. Eight species of Fungi Imperfecti were predominant in the rhizosphere, rhizoplane and macerated root tissue. Of the Fungi Imperfecti 31.5% were common to the rhizosphere and the rhizoplane; 23.7% common to rhizosphere and macerated root tissue. All the isolates from the macerated root tissue occurred in the rhizoplane. Most of the fungi growing on the roots, and obtained by direct observation, were not recovered by culturing.