Randolph S. Currah

The mycorrhizal status of the dominant vegetation along a peatland gradient in southern boreal Alberta, Canada

We investigated the mycorrhizal status of the dominant vascular plant species occurring in ten peatlands along a bog—fen—marsh gradient in southern boreal Alberta in 1997. All members of the Ericaceae were ericoid mycorrhizal, and members of the Salicaceae and Pinaceae were ectomycorrhizal. Also, some members of the Salicaceae and Betulaceae were simultancously ecto- and vesicular-arbuscular mycorrhizal (VAM). Fruiting bodies of the known ectomycorrhizal fungal generaCortinarius, Lactarius, andRussula were collected in late fall. Furthermore, the cosmopolitan ectomycorrhizal taxonCenococcum geophilum was associated with trees and shrubs in all fens and bogs. VA-mycorrhizal fungi were not found in any of the dominant herbaceous plant species in these peatlands; however, vesicles suggesting the presence of VAM fungi were found inCalamagrostis canadensis in the riverine marsh andRubus chamaemorus in the bog. NeitherCarex species in fens and marshes, norTypha latifolia in the lacustrine marsh were mycorrhizal; however, microsclerotia, sclerotial plaques, septate, aseptate, and clamped hyphae were observed to grow on and within cortical cells of their roots. Many of these hyphae were dematiaceous and may belong to theMycelium radicis atrovirens complex (MRA), partially consisting of the endophytic fungal generaPhialocephala andLeptodontidium. Hyphac resemblingRhizoctonia were also observed, although definitive identifications were not attempted. The ecological significance of MRA genera remains largely unknown. Thus, the dominant vegetation in southern boreal bogs and fens is mycorrhizal, possibly enabling these plant species to proliferate in these nutrient-poor ecosystems by accessing otherwise unavailable nutrient pools. In contrast, marsh vegetation is generally non-mycorrhizal, possibly due to higher surface-water nutrient concentrations and fluctuating water levels.

Suppression of Verticillium Wilt in Eggplant by Some Fungal Root Endophytes

One hundred and twenty-three fungal isolates were obtained from 225 root segments of eggplants, melon, tomato, strawberry and Chinese cabbage, grown as bait plants in a mixed soil made up of samples from different fields in Shizuoka, Japan. Isolates belonging to Mycelium radicis atrovirens (MRA), including Phialocephala fortinii, were the most prevalent in all the five bait plants. Eleven of the 123 isolates, after being inoculated onto axenically reared eggplant seedlings, almost completely suppressed the pathogenic effects of a post-inoculated, virulent strain of Verticillium dahliae. Seven of these 11 isolates had come from the roots of eggplant and included Heteroconium chaetospira,P. fortinii, and unidentified species of Fusarium, Penicillium, Trichoderma and MRA. P. fortinii, H. chaetospira, a non-sporulating isolate with white mycelium (SWM) and MRA were easily reisolated from root segments. Hyphae of H. chaetospira, P. fortinii and SWM colonized the root tissues of eggplant without causing apparent pathogenic symptoms. The mechanisms by which these endophytes confer resistance to infection by V. dahliae are unknown but the effectiveness of these fungi in a laboratory setting indicates that they have potential as biocontrol agents and merit further investigation.

Distribution and molecular characterization of the root endophyte Phialocephala fortinii along an environmental gradient in the boreal forest of Alberta

Phialocephala fortinii is a common root endophytic fungus with a wide geographic distribution and little, if any, host specificity. Little is known about its habitat specificity, although there is evidence to suggest that high water tables may restrict the occurrence of P. fortinii in wetlands. We tested this hypothesis by determining the distribution of P. fortinii along a sand dune – wetland complex. Isolates of P. fortinii, identified on the basis of cultural and morphological characteristics, were obtained from the roots of vascular plants across the moisture gradient. Three ‘cultural groups’ were recognized among these isolates. Thirty-three of these isolates were compared among themselves and to strains of known identity using PCR/RFLP analysis of the ITS region and a portion of the 28S subunit of rDNA. The restriction digest profiles of all isolates were identical to those of P. fortinii for 4 restriction enzymes. DNA sequences, from a subset of these strains, showed a low percent sequence divergence confirming the reliability of the RFLP data. The same analyses were done with two strains of Leptodontidium orchidicola a culturally similar root endophyte, to ensure that this taxon was not among the transect isolates. DNA data showed a clear difference between P. fortinii and L. orchidicola but did not discriminate among cultural groups. Thus, P. fortinii showed no habitat specificity and occurred in both xeric and hydric sites. RFLP profiles and ITS sequences showed little variation among isolates of P. fortinii and among the isolates of L. orchidicola.

The Genus Oidiodendron: Species Delimitation and Phylogenetic Relationships Based on Nuclear Ribosomal DNA Analysis

Nuclear ribosomal DNA sequences (ITS region) of fifteen species in the hyphomycete genus Oidiodendron and ten species from the 4 genera in the Myxotrichaceae, Byssoascus, Gymnostellatospora, Myxotrichum, and Pseudogymnoascus, were analysed to: (i) reveal the levels of intra- versus interspecific sequence variation within the genus Oidiodendron, clarify species delimitation and examine the useful- ness of some morphological characters used for iden- tification; (ii) assess the possible conspecificity of doc- umented ericoid mycorrhizal strains of Oidiodendron; and (iii) test the hypothesis based on morphological inference that the genus Oidiodendron belongs with the genus Myxotrichum in the Myxotrichaceae (Ony- genales). Comparison of molecular and morpholog- ical data for multiple strains of 0. griseum, 0. tenuis- simum and 0. maius revealed that conidiophore length and the production of a diffusing pigment are not reliable key characters for the genus. Several his- torically important ericoid mycorrhizal strains, doc- umented as 0. griseum, were reidentified as 0. maius. Parsimony analyses of 23 Oidiodendron strains showed that three highly supported monophyletic groups, each one consisting of a pair of species, are resolved within the genus. A low level of sequence divergence between the species in these pairs suggests conspe- cificity for each pair. Other interspecific relationships were not well-supported by bootstrap values. Parsi- mony analysis of a second dataset composed of mi- totic and meiotic taxa showed that Oidiodendron, My- xotrichum and Byssoascus form a well-supported monophyletic group within the Myxotrichaceae, and

Succession of microfungal assemblages in decomposing peatland plants

We investigated the microfungal assemblages in the decomposing tissues of dominant plant species in two peatlands in southern boreal Alberta, Canada, to determine if distinct patterns of succession of microfungi occurred throughout the first two years of decomposition. These plant species were Sphagnum fuscum from a bog and Carex aquatilis leaves and rhizomes and Salix planifolia leaves and roots from a riverine, sedge-dominated fen. Canonical correspondence analyses, a multivariate statistical analysis used infrequently in mycological research, revealed distinct patterns of fungal species succession in two of the five litters (S. fuscum and C. aquatilis leaves). Furthermore, our analyses showed that substantially different microfungal assemblages were associated with these litters within the first two years of decomposition. Litter quality variables, such as total nitrogen, total phosphorus, and total carbon tissue nutrient concentrations, explained most of the succession patterns and differences in the microfungal assemblages of these five litters. Our data did not reveal the classical taxonomic zygomycete – ascomycete/fungi imperfecti – basidiomycete pattern of succession during organic matter decomposition. Similarly, a succession of functional groups of microfungi, i.e., cellulose-degraders preceding lignin-degraders, generally was not apparent. Instead, microfungi with broad spectra of enzymatic abilities co-existed over the first two years of decomposition in these peatland plant litters. These microfungi have a limited ability to decompose complex phenolic polymers, such as lignin, resulting in the accumulation of peat in these ecosystems. Some microfungal taxa were not affected by changes in litter quality, environmental variables, or surface water chemistry and were present at all stages of decomposition.

Microfungi isolated from Sphagnum fuscum from a Southern Boreal Bog in Alberta, Canada

Abstract Microfungi were isolated from living and decomposing Sphagnum fuscum from a southern boreal bog in Alberta, Canada. Fifty-five fungi (three ascomycetes, three basidiomycetes, 11 zygomycetes, 28 Fungi Imperfecti, 10 unnamed mycelia sterilia) are described in this study. Of the Fungi Imperfecti, 21 species have known sexual states (teleomorph) in the Ascomycota, while the remaining seven species are known only from their asexual state (anamorph) and could not be assigned to specific teleomorphic families. Thirty-six species represent new records from Sphagnum and 45 species are new records for S. fuscum. Nearly 52% of the 45 identified fungi originated from three families, Mortierellaceae (10 taxa, Zygomycota), Trichocomaceae (8 taxa, Ascomycota), and Hypocreaceae (5 taxa, Ascomycota), with the remaining fungi representing 12 additional families. The 55 fungi have the ability to utilize a variety of carbon sources, such as cellulose, tannic acid, and pectin, and thus are important organisms involved the mineralization of carbon in peatlands.

An integrated approach to Rhizoctonia taxonomy: cultural, biochemical and numerical techniques

Twenty-five isolates of Rhizoctonia , comprising 12 anastomosis group strains belonging to R. solani and 13 isolates from orchids, were compared on the basis of cultural characteristics on a variety of media, of effects on growth to varying pH and carbon and nitrogen sources, and enzymic abilities. Data were coded and analysed using the computer programs taxmap, taxpac and numipac . The orchid isolates, although exhibiting significant variation among themselves, were distinct from the R. solani anastomosis groups. Results support recognizing AG4 as a distinct species, Thanatephorus praticola , but do not support recognizing T. sasakii or Corticium microsclerotium as taxa distinct from T. cucumeris . Orchid isolates were separated among three diverse groups representing T. pennatus, R. repens , and a final large and diverse group consisting of R. anaticula, Ceratobasidium obscurum and several unidentified isolates.

Comparative Morphology and Phylogenetic Placement of Two Microsclerotial Black Fungi from Sphagnum

Capnobotryella renispora and Scleroconidioma sphagnicola form black, irregularly shaped microsclerotia that are indistinguishable in gross morphology on leaves of Sphagnum fuscum. In culture, microsclerotia of these fungi were similar, in that mature component cells possessed thick, highly melanized cell walls, poorly defined organelles, large lipid bodies and simple septa. They were different in morphogenesis, in the way their component cells were organized and in disseminative propagules. Microsclerotia of S. sphagnicola formed phialidic conidiogenous cells on their surface, whereas in C. renispora, adjacent cells in mature microsclerotia often separated from each other by septum schizolysis and formed chlamydospores. The identification of C. renispora from Sphagnum is provisional despite a 100% ITS sequence match with data for a culture derived from the type strain. No holoblastic, reniform conidia typical of the species were formed in nature or in culture, and the SSU sequence for a separately preserved culture of the ex-type strain was markedly divergent. Parsimony analyses of nuclear ribosomal DNA sequences showed that these two fungi were related to separate orders of Dothideomycetes. Both SSU and ITS data supported a close relationship for S. sphagnicola to the Dothideales sensu stricto, while the closest ITS match was to Rhizosphaera spp. In the SSU analyses, C. renispora was nested within the Capnodiales.

Saprobic characteristics of three fungal taxa from ericalean roots and their association with the roots of Rhododendron groenlandicum and Picea mariana in culture

Abstract. Simultaneous associations among ectotrophic and ericoid mycorrhizal hosts and their mycorrhizal fungi are expected in boreal bogs where ericaceous shrubs and conifers coexist rooted in an organic matrix dominated by Sphagnum mosses. We were thus prompted to examine, in vitro, the abilities of three ericoid mycorrhizal fungi [Hymenoscyphus ericae, Oidiodendron maius, and Variable White Taxon (VWT)] to associate with Picea mariana (Pinaceae), with both P. mariana and Rhododendron groenlandicum (Ericaceae) simultaneously, and to decompose Sphagnum fuscum. Hymenoscyphus ericae and VWT developed an intracellular association with roots of P. mariana and with roots of R. groenlandicum. Two strains of O.maius did not form typical infection units in R. groenlandicum, nor did they colonize the root cells of P. mariana. Mass losses incurred by sterilized S.fuscum plants inoculated with these three taxa indicated that O. maius could be more efficient as a free-living saprophyte on this material than either H. ericae or VWT and may in part explain why atypical associations with the roots of ericaceous hosts were formed.

Septal ultrastructure of some fungal endophytes from boreal orchid mycorrhizas

The septal ultrastructure of nine fungal endophytes from mycorrhizas of boreal orchids was examined to corroborate identifications made previously on the basis of cultural and microscopic characteristics. Leptodontidium orchidicola has a simple septum perforated by a single central pore flanked by Woronin bodies. Epulorhiza anaticula, E. repens , and a Sebacina sp. all have dolipore septa with flattened septal pore caps some of which have a minute single central perforation. Ceratobasidium cornigerum, C. obscurum, Moniliopsis anomala, Thanatephorus pennatus and Sistotrema sp. have dolipore septa with dome-shaped, perforated septal pore caps.