A wide range of ascomycetous microfungi inhabits roots without forming the anatomical features typical of mycorrhizas or causing overt signs of pathogenesis. The most-studied taxa have darkly pigmented hyphal walls and are referred to as "dark septate endophytes" (DSE). We provide a dichotomous key and annotated descriptions for a cross-section of the most common dark septate endophytes. The term DSE is sometimes used to imply taxonomic and physiological similarity even though a diverse range of root endophytic taxa form pigmented hyphae. Among these, Phialocephala fortinii Wang & Wilcox is a well-known representative; it is widespread, easily observed in roots, and readily grown in culture and with plants. Nevertheless, the basis of its symbiotic relationship with plants remains ambiguous. It may be a weak pathogen, a saprotroph on senescent root tissues, or a mutualist. More detailed studies of interactions between identified taxa of microfungal endophytes and host plants are necessary to elucidate the functional basis of these symbioses; it may be necessary to look beyond the paradigms of traditional mycorrhizal and pathogenic associations to understand the ecological roles of these fungi. Reports of cryptic speciation in Phialocephala fortinii emphasize the need for accurate identification of isolates of microfungal endophytes used in experiments.Key words: dark septate endophytes (DSE), Phialocephala fortinii, mycorrhiza, fungus–host interactions, fungi.

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The relationships among winter cover cropping, inoculum potential of vesicular-arbuscular mycorrhizal (VAM) fungi, and the growth and yield of a subsequent maize crop were investigated. In the first experiment, an autumn-sown winter wheat cover crop increased VAM fungal inoculum potential of a field soil as measured by an in situ maize bioassay during the following growing season. Infective extra-radical hyphal densities were significantly increased by cover cropping as interpreted from the effect of soil disturbance on infection of the maize bioassay plants. In a second experiment the following year, the winter wheat cover crop again increased VAM fungal inoculum potential as assessed by an in situ maize bioassay during the following growing season. Moreover, the degree of mycorrhizal infection of maize was correlated with maize growth and yield. This study suggests that the management of mycorrhizal fungi by cover cropping may be a useful practice in sustainable agriculture.

Dark septate root endophytic fungi from plants growing on either side of an abrupt wetland–upland ecotone included isolates of Phialocephala fortinii Wang & Wilcox, Leptodontidium orchidicola Sigler & Currah, Hetero conium chaetospira (Grove) Ellis, and a hitherto undescribed fungus resembling P. fortinii. Six isolates of this species were recovered and were distinctive in (i) producing an orange–tan diffusible pigment in culture, (ii) causing a yellow colour shift on casamino acids medium containing bromocresol purple, (iii) having the ability to liquefy gelatin, and microscopically, (iv) forming hyaline conidia from phialides arranged in large spherical heads after prolonged incubation at 5 °C. First-formed or primary conidia are bullet shaped, 1–1.5 µm × 2–3 µm; subsequent conidia are spherical and 1–1.5 µm in diameter. Small subunit and internal transcribed spacer region sequence comparisons with P. fortinii and other Phialocephala species supported placing these six unique strains in a new species, Phialocephala sphaeroides B.J. Wilson sp. nov. Phylogenetic analyses also suggest that P. sphaeroides is affiliated with mollisioid taxa in the Dermateaceae. In contrast with P. fortinii, which was isolated on both sides of the ecotone, P. sphaeroides was obtained only from plants in the highly acidic, Sphagnum-dominated wetland habitat and not from the same species in the less acidic, aspen-dominated upland site.Key words: inoperculate discomycetes, phialidic anamorph, Helotiales, root endophytes, Loramycetaceae, Dermateaceae, Mollisia.