Successional patterns of fungal communities in needles of European silver fir (Abies alba Mill.).

Successions of fungal communities in mature, senescing and decomposing needles of silver fir (Abies alba Mill.) were studied at two sites in Switzerland. These were in naturally regenerated forest (Ruswil) on soils of pH 4.0 to 4.5 and in planted forest (Üetliberg) on soils of pH 6.5 to 7.0. Attached green symptomless needles of two age classes (1- to 2 and 4- to 7-yr-old), partly brown senescent needles, entirely brown needles and litter needles were collected, surface-sterilized and incubated on 2% MEA amended with 50 mgl-1 terramycin to isolate fungi from within the tissues. Litter needles were collected in nylon nets (litter collectors) placed on the ground to facilitate good litter-soil contact. One hundred and twenty species were isolated from green symptomless needles and more than 140 from litter needles. Species could be classified in three groups according to their habit: (1) endophytes of living needles, (2) colonizers and endophytic survivors in senescent tissues, newly dead attached, and litter tissues, and (3) those which colonized needle litter only. Among the frequently isolated species, only Exophiala sp. 1 and Grovesiella abieticola (Zeller & Goodding) Morelet & Gremmen belonged exclusively to the first group. Cryptocline abietina Petrak and Gloeosporidiella sp. also belonged to this group but could occasionally be isolated from fresh litter. Prominent representatives of the second group were Cytospora pinastri Fr., Hormonema dematioides Lagerb. & Melin, Rhizosphaera oudemansii Maublanc, R. macrospora Gourbière & Morelet, and Leptostroma sp, The frequency of colonization by members of this second group, for which the term 'transition-fungi' has been introduced, decreased quickly after needle fall. Transition-fungi were fully substituted within one year after needle fall by members of the third group, such as Thysanophora penicillioides (Roum.) Kendrick, Rhizoctonia sp. 1, Gliocladium penicillioides Corda, Pseudo-microdochium sp., Cylindrocladium sp. or Coleophoma cylindrospora (Desm.) v. Höhn. Successional patterns of discrete fungal populations were significantly affected by both edaphic conditions and forest management. At Ruswil, in decreasing order of frequency, Cryptocline abietina, Gloeosporidiella sp., Grovesiella abieticola and Leptostroma sp. were the dominant species in attached green needles, as were Hormonema dematioides, Cryptocline abietina, Leptostroma sp., Rhizosphaera macrospora and R. oudemansii in partly brown and entirely brown needles, and as were Thysanophora penicillioides, Rhizoctonia sp. 1 and Gliocladium penicillioides in needle litter. In contrast, fungal communities at Üetliberg were dominated by Exophiala sp. 1 and Grovesiella abieticola in attached green needles, by Cytospora pinastri and Exophiala sp. 1 in partly and entirely brown needles and by T. penicillioides, Coleophoma cylindrospora, G. penicillioides and Cytospora pinastri in litter needles. Differences in the frequency of fungal colonization of litter needles existed also between the litter collectors. However, differences were significant only for Pseudomicrodochium sp. and Cylindrocladium sp. at Ruswil. Attached green needles were collected and buried in the litter layer close to the litter collectors in an additional experiment. Species composition was the same in buried and in naturally fallen needles at Ruswil but not at Üetliberg, where Cytospora pinastri did not occur in buried needles, i.e. colonization by this most frequent transition-fungus was missed out. Conversely, Trichoderma viride was detected only in buried, not in naturally fallen needles, at Üetliberg, where it was among the most frequently isolated soil fungi. T. viride was also the only soil fungus with any potential to colonize fallen needles.

Correspondence analysis as a tool in fungal taxonomy.

The polyphasic approach to taxonomic problems has led to the creation of complex datasets that lend themselves to numerical analysis. The numerical study, however, has to deal with mathematical problems linked with the presence of mixed-type data originating from the investigations. Correspondence analysis (CA) is an ordination technique widely used in ecology and social sciences but only rarely applied to taxonomic problems. In CA corresponding variables and taxa ordination are obtained simultaneously, thus allowing to explore the taxonomic interrelationships between taxa and variables in a single analysis. CA can be used on large and small datasets, and can be applied to mixed-type data after appropriate coding. It is not sensitive to variation of class number and size and is useful to screen large unstructured datasets, to suggest which variables should be retained to discriminate samples, to detect outliers or erroneous data and to perform identification of unknown samples. It also has the advantage of handling missing data particularly well. On the other hand, CA is sensitive to outliers, which can cause a distortion of the geometric map of the points in the graphical display. Nevertheless, the sensitivity of correspondence analysis to outliers can be effectively used to verify data. Finally, based on symmetry of row and column analyses correspondence analysis can be applied to find out which characters can be used to construct identification keys and to selectively group variables by their importance for the discrimination of samples.

Stereum sanguinolentum: Is it an amphithallic basidiomycete?

Monobasidiospore isolates were prepared from basidiocarps of Stereum sanguinolentum. Five isolates per basidiome were paired with each other and with isolates from the trama. Interbasidiome pairings of the trama isolates and of a selection of single-spore isolates also were performed. Thin sections of the hymenium were stained with DAPI and examined by fluorescence microscopy to study the nuclei in the basidia. Spore prints were stained with DAPI to count the number of nuclei per spore. SEM was used to determine the number of basidiospores per basidium. All intrabasidiome pairings were compatible. In contrast, interbasidiome pairings, except one, were incompatible, independent of whether single-spore or trama isolates were paired. Fertile basidiomes were formed in single-basidiospore cultures. Basidia were regularly four-spored. On average, 5% of the basidiospores possessed one nucleus, 82% two, 2% three and 1% four nuclei. Ten percent of the spores appeared to be empty. Karyogamy, meiosis and postmeiotic mitosis were observed in the basidia. Nuclei resulting directly from meiosis, i.e., without having undergone postmeiotic mitosis, sometimes were observed in the sterigmata or spore primordia. The high number of vegetative compatibility groups (VCG) of S. sanguinolentum observed in this study and earlier studies is difficult to explain without sexual or parasexual recombination. We suppose that the majority of spores with ≥2 nuclei are amphithallic, possessing at least one nucleus of each mating type. Recombination could occur by exchange of nuclei among VCGs via anastomoses between homothallic compartments. Transfer of nuclei from heterothallic to homothallic mycelia or matings between homothallic mycelia, which originate from monokaryotic spores, might be other paths for gene exchange.

Microsatellite size homoplasies and null alleles do not affect species diagnosis and population genetic analysis in a fungal species complex.

The suitability of 13 microsatellite loci for species diagnosis and population genetics in 11 species of the Phialocephala fortinii s.l.-Acephala applanata species complex (PAC) was assessed. Two data sets were compared to test possible biases in species typing and clone detection resulting from null alleles and size homoplasies. The first data set was based on fragment lengths derived from a multiplex polymerase chain reaction (PCR) assay and the second data set was received from singleplex PCR at lower stringency and sequencing. Most null alleles observed in the multiplex PCR assay could be amplified during singleplex PCR under less stringent conditions. Size homoplasies resulting from mutations in flanking regions and differences in microsatellite structures were observed. For example, Phialocephala uotolensis possessed a (CT)(13) in addition to the (GT)(x) motif at locus mPF_0644. Despite the occurrence of null alleles and size homoplasies, species diagnosis and population genetic analysis studies were not affected. These markers will facilitate studies on population biology, ecology and biogeography of PAC species.

Fragmented environment affects birch leaf endophytes.

The effect of environmental fragmentation on the species distribution and frequency of horizontally transmitted endophytic fungi in Betula pubescens and Betula pendula leaves was studied in an archipelago in southwestern Finland. The study system consisted of 14 islands, ranging in size and distance to the mainland, and five mainland sites. Endophytic fungi were grown out from surface-sterilized leaves. The frequency of endophytic fungi mainly depended on the size of the island, explaining 32-35% of the variation, and the distance to the mainland explaining 29-35% of the variation. The birch trees on the largest islands near the mainland had the highest endophyte frequencies. Fusicladium betulae, Gnomonia setacea and Melanconium betulinum were the most commonly isolated fungi. Foliar endophytes of birch trees are able to disperse to fairly fragmented areas, but their frequencies seem to depend on environmental isolation and size of the island.

Ecology, metabolite production, and substrate utilization in endophytic fungi.

Endophytic fungi are a taxonomically and ecologically heterogenous group of organisms, mainly belonging to the Ascomycotina and Deuteromycotina. The isolation methods affect the species composition of the endophyte assemblage in a given host. The number of endophyte taxa isolated from a host species is usually large; however, only few, normally host specific species or strains are dominant. Endophyte assemblages are specific at the host species level, but species composition and frequencies are significantly affected by site-specific conditions. Moreover, the relative importance and number of endophytic species vary among individuals within sites. In some cases, each individual could be considered a separate ecosystem. In general, however, 40 individuals with 30 to 40 sampling units per organ and individual should be enough to detect 80% of taxa present in a given host at one site. Endophytes usually produce the enzymes necessary for the colonization of plant tissues. Substrate utilization studies and isozyme analysis have demonstrated that most endophytes are able to utilize most plant cell components. The production of growth promoting factors and of metabolites useful in the pharmaceutical and agricultural industry is widespread among endophytic fungi. The usefulness of endophytes in agricultural and pharmaceutical research is briefly discussed.