Martha Christensen

Infrageneric Taxa of Aspergillus

The species of Aspergillus fall into distinct clusters, which have been widely accepted. Since Thom and Church (1926), Thom and Raper (1945) and Raper and Fennell (1965), these clusters have been called “groups”, a category without nomenclatural standing. In a few cases “series” were named, which do have a nomenclatural status (when described before 1935 even without a Latin diagnosis), but they do not compete for priority unless at the same rank. For the sake of simplicity in citation, we prefer to introduce new sections rather than new combinations from previous series. In contrast, in Penicillium subgenera and sections were named at the beginning of the century and a complete scheme was formally devised by Pitt (1979).

A SYNOPTIC KEY AND EVALUATION OF SPECIES IN THE ASPERGILLUS FLAVUS GROUP

SUMMARY A synoptic key for identification of 16 taxa in the Aspergillus flavus group is presented. The key uses definitive and readily observable features: vesicle size, color of conidial heads, conidiophore and conidium features, growth at 37 C, and form and size of sclerotia. Brief descriptions are included as an aid to identification. The authors interpretation of relatedness among species, based upon morphological and cultural data and involving an ordination using coefficients of similarity, is compared to results from chemotaxonomic studies by other workers. A distributional and ecological analysis has been based upon examination of species lists in nearly 100 surveys. Aspergillus leporis, A. avenaceus, A. sojae, A. subolivaceus, and A. zonatus, in particular, are interpreted as morphologically and ecologically distinct species. Aspergillus flavus, A. oryzae, and A. parasiticus are in part domesticated species with broad and overlapping morphologies. Aspergillus toxicarius appears to be a biseriate form of A. parasiticus, and A. kambarensis probably belongs with A. oryzae. Additional isolates of Aspergillus leporis States & Christensen (65) from cool desert soils in Wyoming, southern Utah and northern Arizona, and isolation of a closely related taxon, also tightly columnar but with elongate, cream to russet sclerotia, stimulated a comparative study of species in the A. flavus group. The distinctive strain, 0 168, is a variant of A. leporis and is mentioned again in the brief description of that species. Aspergillus leporis is distinguished from A. flavus Link in the key and in the descriptions; it is not a synonym of A. flavus as has been suggested (59). The key was written with the intention of providing a practical guide to identification of species in the A. flavus group. Evaluations of synoptic keys and suggestions regarding their use can be found elsewhere (18, 39). The A. flavus group as described by Raper and Fennell (54) contained nine species. Since 1965, five species and four varieties have been newly described (6, 41, 48, 59, 65, 67), A. sojae Sakaguchi & Yamada, listed as a probable synonym of A. parasiticus Speare by Raper and Fennell, has been elevated to species status again (48), and A. corolligenus (Massee) Subram. and A. insecticola Subram., originally described in 1910 and 1879, respectively, have been transferred to Aspergillus, A. flavus group, from Sterigmatocystis Cramer (66). 1056

Population variation in the mycorrhizal fungus Glomus mosseae: breadth of environmental tolerance

Responses to a range of environmental conditions were examined and compared in three populations of Glomus mosseae from dissimilar habitats to assess phenotypic plasticity. The G. mosseae populations were observed (1) in three soils with different physical-chemical characteristics, (2) at three different levels of soil moisture and (3) under three temperature regimes. Using Melilotus officinalis as host, measurements were made of mycorrhiza formed, spore production and influence of the endophytes on host biomass production and shoot phosphorus concentration. The three G. mosseae populations were found to vary significantly in their responses under different environmental conditions and in their breadth of tolerance to environmental factors. Results were interpreted as indicating that phenotypic plasticity is variable among populations of G. mosseae but not sufficient to explain the wide distribution of this fungus.

THE ASPERGILLUS OCHRACEUS GROUP: TWO NEW SPECIES FROM WESTERN SOILS AND A SYNOPTIC KEY

Two new species in the Aspergillus ochraceus group are described and compared to related taxa. Aspergillus bridgeri, from soils collected in a native community dominated by Atriplex gardneri in Wyoming, somewhat resembles A. elegans and A. lanosus, but differs in cultural and morphological details. Aspergillus campestris, from a native prairie in northern North Dakota, resembles A. dimorphicus in having metulae that are up to 35-45 im long, but is a more restricted form with yellow conidial heads, taller conidiophores, occasionally septate metulae, and ellipsoidal conidia. A synoptic key is presented as an aid to identification of species in the A. ochraceus group-an assemblage which has increased considerably since 1965 and currently embraces 15 species. Brief descriptions of the species accompany the key along with distributional and ecological analyses prepared from species lists in more than 130 published surveys.

Fungi Associated with Biological Soil Crusts in Desert Grasslands of Utah and Wyoming

Biological soil crusts of arid and semiarid regions of the world are recognized as one of the least explored niches occupied by fungi. The principal species of fungi associated with biocrusts in desert grasslands and their associated soils in two geographically separated sites were identified and compared with species from a similar community in which the active crust had been destroyed by grazing. The results confirm the existence of a highly diverse and to some degree a host specific assemblage (mycosociety) of fungi. Comparison of the prevalent species by presence and commonness at the undisturbed and disturbed sites revealed both quantitative and qualitative changes. The forms absent or with a markedly reduced occurrence in the disturbed site were three dark-colored anamorphs of loculoascomycetes (Bipolaris sp., Embellisia tellustris, Phoma anserina) and two loculoascomycetes (Graphyllium permundum, Pleospora richtophensis). Fungi present at all sites included Chrysosporium/Geomyces pannorum, Embellisia tellustris and Pseudozyma sp. Crust associated fungi not previously reported from soil included a basidiomycete (Cyphellostereum sp.), five loculoascomycetes (Kalmusia utahensis, Macroventuria wentii, Pleospora richtophensis, Phaeospora sp., Preussia sp.) and three mitosporic species (Heteroconium sp., Sclerococcum sp., Taeniolella sp.). Overall, the commonly encountered crust-associated fungi were dark-colored mitosporic and sterile forms apparently adapted to desert environments.

Fungal presence in paired cultivated and uncultivated soils in central Iowa, USA

Abstract Amounts of fungal biomass in adjacent cultivated and uncultivated soils in central Iowa were estimated and compared by quantifying soil ergosterol concentrations and lengths of fungal hyphae present. Both indices of fungal biomass, with one exception, indicated that there was at least twice as much fungal biomass in uncultivated soil as in cultivated soil. Levels of microbial biomass carbon in uncultivated soils were also determined to be at least twice that in cultivated soils. Data collected in this study indicate that fungi may be more significantly affected by agricultural soil management practices than other components of the soil microbial community. For two of the soils examined, calculated estimates denote that fungal biomass carbon represented approximately 20% of the total microbial biomass carbon in cultivated soil and about 33% of the microbial biomass carbon in uncultivated soil. Results of this study indicate that conventional agricultural practices result in a significant reduction of fungal biomass production in soil. Implications of differences in fungal biomass between the soils are discussed.

In vitro mycelial interactions among members of a soil microfungal community

Abstract In vitro interactions among seven members of a soil microfungal community were examined and characterized to provide information on how interactions may influence fungal community structure in soil. Behaviors of species in paired culture was observed on three media with different nutrient resources (malt, dilute cornmeal and water agar) in Petri dishes and on microscope slides.All isolates used in this study were in some way affected by the presence of another fungus; usually growth was inhibited. Outcomes of mycelial interactions after growth for 4 weeks or more were categorized as: (1) neutral intermingling, (2) deadlock and (3) replacement.Deadlock, in which neither mycelium can enter territory occupied by the other, was the most commonly observed outcome of the pairings except on low-resource media, where neutral intermingling was the commonest class of interaction.Our results suggest that fungal community structure under oligotrophic conditions is not highly territorial, but mycelia become more territorial and combative when colonizing relatively resource-rich microhabitats or substrates.

Synoptic key to Aspergillus nidulans group species and related Emericella species

A synoptic key for identification of 30 taxa in the Aspergillus nidulans-Emericella assemblage is presented. The key uses definitive and readily observable features : conidiophore length, width of conidial columns, hulle cell distribution and colour in mass, ascospore morphology, location of cleistothecia in relation to hulle cells, and, for certain taxa, colony appearance with specified growth conditions. Brief descriptions are included as an aid to comparison and to guide the reader to detailed technical descriptions.

MYCORRHIZAL FUNGI ASSOCIATED WITH BOUTELOUA AND AGROPYRON IN WYOMING SAGEBRUSH-GRASSLANDS

The spore populations of vesicular-arbuscular (VA) mycorrhizal fungi at four sagebrushgrassland sites in Wyoming were examined, characterized, and quantified. The sampled soils contained 232-696 spores per 100 g dry soil and three to six species of VA mycorrhizal fungi (Glomus fasciculatus, G. macrocarpus, G. microcarpus, G. mosseae, Entrophospora infrequens, and an unidentified form). Community composition and relative prominence (frequency, density) of the six species were related both to geographic location of the site and abiotic factors and to identity of the plant symbiont. Environmental influence on spore populations is discussed.

Aspergillus: An Overview

Since 1965, approximately 80 species in Aspergillus have been described as new and thousands of publications have contributed to our knowledge of biochemical and ultrastructural features. The group concept, developed in the monographs of 1926, 1945 and 1965 has been a tremendous aid in species identification. Sixteen of Raper and Fennell’s 18 groups have been validated by the contributions of the last 20 years. Only the A. ornatus and A. wentii groups appear to be heterogenous. An analysis of the Aspergilli listed in 62 recent soil surveys has revealed highest absolute and relative numbers of species in the subtropics, particularly in cultivated soils, saline soils and subtropical deciduous forest soils. In temperate regions, highest numbers of species have been reported from desert soils and certain grassland soils. Unusual species in the soils of western US intermountain basins may have evolved following early migration, then isolation and specification through the Pleistocene.