Morphogenesis is not simply a matter of playing out a predefined genetic programme. Expression of developmentally important genes is epigenetic and place- and time-dependent relying on previously-formed tissue structures. Most differentiated hyphal cells require reinforcement of their differentiation ‘instructions’. This reinforcement is part of the context (chemical, electrical and structural/mechanical environment) within which they normally develop. Key words at each stage of development in fungi are: competence, induction and change. Fungal morphogenesis is compartmentalized into a collection of ‘sub-routines’ which are distinct genetically and physiologically. Flexibility in expression of developmental sub-routines illustrates that tolerance of imprecision is an important attribute of fungal morphogenesis.

Techniques for selective isolation, semiquantification and rapid virulence testing are described for Catenaria anguillulae, an important endoparasitic fungus of nematodes. Selective isolation was achieved by using second-stage juveniles of Anguina tritici as bait in soil aliquots for 48 h. Semiquantitative estimation of the population of the fungus was made by calculating the infection percentage of inoculated juveniles. Rapid virulence testing was done by using second-stage juveniles of Heterodera cajani, Meloidogyne incognita and A. tritici.

Cladistic analysis of characters derived from nuclear-encoded 18S rDNA sequences was used to infer the phylogenetic placement of ambrosial species of the anamorph genus Raffaelea among perithecial ascomycetes. Of eight species in the genus investigated, seven resolve as a monophyletic lineage that forms a sister group to the sexual genus Ophiostoma. Raffaelea hennebertii, the single species excluded from this lineage, appears to be allied phylogenetically with species of Melanospora. These data are discussed in relation to the monophyly of Raffaelea and its relationship with other sexual and asexual fungal associates of wood-boring Coleoptera. In addition, we report the presence of significant length variation in PCR-amplified 18S rDNA fragments for three of the Raffaelea species studied.

Two rapid, independent molecular assays have been developed for discriminating between the closely related rusts of hard pines, Cronartium flaccidum and Peridermium pini. A portion of the ITS region and a portion of the IGS region from the ribosomal RNA operon of the two organisms were amplified with the PCR. Amplifications were made using DNA extracted from aeciospores collected from unopened aecia, taking a small number of spores as a source of template DNA. Amplified fragments were subjected to RFLP or to SSCP analysis. Digests of the amplified products from the IGS1 region were electrophoresed on polyacrylamide gel and stained with ethidium bromide. Hinf I digestion of these fragments created polymorphic restriction profiles which allowed differentiation of the autoecious P. pini from the heteroecious C. flaccidum. Similar-sized DNA fragments representing the ITS2 region of the two rusts were denatured, subjected to electrophoresis as single strands on polyacrylamide gel under non-denaturing conditions and ‘silver stained’. The different mobility displayed by these short fragments revealed sequence polymorphism in the examined portion of the ITS region. This technique therefore represents an accurate and sensitive method for detection of base changes in given sequences of genomic DNA. A high level of homology was found between the two biotroph organisms in the loci screened. Results obtained in this trial indicate that PCR-RFLP and PCR-SSCP can be used as simple, speedy taxonomic tools for elucidating relationships among related organisms.

Cladobotryum dendroides, causal agent of cobweb disease of Agaricus bisporus, has become increasingly resistant to methylbenzimidazole carbamate (MBC) fungicides following the extensive use of MBC in cultivated mushroom production in Ireland. Of 38 isolates of C. dendroides obtained from Irish mushroom units, 34 were resistant to carbendazim. Primers based on conserved regions of the β-tubulin gene were used to amplify and sequence a portion of the β-tubulin gene in C. dendroides. A point mutation was detected at codon 50 in isolates resistant to benzimidazole fungicides, causing an amino acid substitution from tyrosine to cysteine. Species-specific PCR primers were designed to amplify the region of the β-tubulin gene containing this substitution. The point mutation removed an Acc I restriction site in the β-tubulin gene sequence of resistant isolates. Digestion of the PCR product with Acc I thus provides a rapid diagnostic test to differentiate sensitive and resistant isolates of this fungus. EMBL accession number: Y12256.

The influence of Fosetyl-Al and Metalaxyl on the diversity of arbuscular mycorrhizal fungi (AMF) was evaluated on naturally established citrus plants. Thirteen AMF species were recovered from rhizospheres of Citrus sinensis/C. limon treated or not with Fosetyl-Al and/or Metalaxyl. Spores of AMF were obtained from 100 g of rhizospheric soil at two sites in São Paulo state, Brazil. The soil samples were treated by the wet-sieving technique and the spores were quantified and identified. The number of spores was low at both sites. Fosetyl-Al reduced the number of spores and the diversity of AMF in one site but not in the other. Metalaxyl at low concentration increased the diversity of species in some experiments, but at higher concentration it tended to reduce the number of spores of AMF. Scutellospora was the genus that presented the largest number of species (7) followed by Acaulospora (3), Glomus (2) and Gigaspora (1). Gigaspora ramisporophora was the dominant species in one site, Glomus macrocarpum and Scutellospora gilmorei were dominant at the other.

Arthrobotrys chazarica sp. nov. and Nematophagus tabrizicus sp. nov., which capture nematodes by means of adhesive networks, are described and illustrated.

The aim of this work was to use sexual reproduction to introduce new genotypes into natural populations of Cryphonectria parasitica, the cause of chestnut blight disease. Mating was initiated by painting conidia (which serve as spermatia) onto stromata in cankers initiated in the early spring. The matings yielded perithecia 161 and 180 d after canker initiation. Single-ascospore isolates from these perithecia included cultures with the phenotypes of conidia which had been painted onto the cankers as early as 17 d after canker initiation.

Transmission electron microscopy was used to study the development and structure of resting spores and sporosori of Polymyxa graminis. Osmiophilic bodies generally distributed in the cytoplasm moved to the periphery as spores matured. The spore wall consisted of four or five layers, two of which extended into spines linking adjacent spores. An unstained plug in the wall, faced towards the outside of the sporosorus. Some spores germinated in situ by producing primary zoospores. Bundle-like structures in some spores may have been barley yellow mosaic virus particles.

The uredinial stage of Skierka agallocha was detected on leaves of Excoecaria agallocha, collected for the first time from mangroves of the Sundarbans during 1992. This communication deals with light microscope and scanning electron microscope characters of this mangrove rust.

The following foliicolous fungi on Tabebuia species are described and illustrated: Anhelia tabebuiae sp. nov. and Dictyonella tabebuiae sp. nov. (ascomycetes), Fumagospora tabebuiae sp. nov., Polychaeton tabebuiae sp. nov. and Septoria tabebuiae-impetiginosae sp. nov. (coelomycetes), Cercospora tabebuiae-impetiginosae sp. nov. and Pseudocercospora tabebuiae-roseo-albae sp. nov. (hyphomycetes). Uncinula peruviana was found and described on T. impetiginosa as a first record for Distrito Federal, Brazil.

Four new taxa are described, each having multiseptate ascospores with hyaline end cells; Savoryella limnetica, Ascotaiwania wulai, A. hsilio and A. sawada. Savoryella and Ascotaiwania are evaluated and separated by the following characters: Savoryella has broad, up to 8 μm paraphyses (sparse) that are septate and rounded at their ends, and smaller asci with an apical thickening containing a plugged pore and 3-septate ascospores; Ascotaiwania has narrow, filiform, septate paraphyses up to 2 μm wide, but these deliquesce early and are rarely observed in mature ascomata. Ascotaiwania also has asci with a well-developed apical ring and plugged pore and ascospores generally with more than 3 septa. Ultrastructural studies of A. lignicola showed that the ascopores are covered by a thin mucilaginous sheath and unitunicate asci with the wall comprising an outer, 30–40 nm electron-dense layer and an inner, 420–450 nm, thick, electron-transparent layer. Asci have a well-developed apical apparatus consisting of an electron-dense apical ring with a plug. The plug deliquesces prior to ascospore release. The ascospore wall comprises an electron-dense episporium and a less electron-dense mesosporium. External to the episporium is a fibro-granular sheath.

Hyphal growth of the white button mushroom Agaricus bisporus on spawn grains and compost is typically vegetative. Hyphae are loosely arranged, in contrast to the organized texture in tissues, and needle-like calcium oxalate crystals are frequently present on the surface of vegetative hyphae. The mycelial cord is the first well-organized tissue of the fruiting mycelium; it is surrounded by fluffy white hyphae that grow vegetatively. The hyphae of the cord are held together through a semi-fluid medium, the extracellular matrix, which aids in creating a three-dimensional pseudoparenchymatous structure. The matrix material seems to be secreted into the extracellular environment by specifically differentiated cells, but the vegetatively growing hyphae of A. bisporus initially exploit a different mechanism in the production of matrix which involves a type of cell death different from cell necrosis. This primary matrix production leads to the formation of minute cord tissues in which oxalate crystals are no longer present. Once the hyphal cells of A. bisporus pass the threshold from a vegetative form into organized structures, they become differentiated and self-maintaining in the production of the extracellular matrix material. Morphogenetic cell death has been observed before in A. bisporus development and here we show that it occurs in various species of macrofungi: a mucoid zone of the pileipellis typically found in developing fruit bodies of Psilocybe and Panaeolus spp. contains numerous, dying or dead hyphal cells which show ultrastructural features comparable to those observed during the mycelial cord formation of A. bisporus. Studies performed using specimens of Stropharia rugoso-annulata, Coprinus domesticus, Psathyrella candolleana, Tremella mesenterica, Otidea onotica and Peziza ostracoderma in representative growth stages revealed supporting evidence for the view that morphogenetic cell death plays a key role at different stages during the development of fungal fruit bodies. This phenomenon may be related to the programmed cell death occurring in developing plants and animals.

Ancorasporella mexicana gen. et sp. nov., collected on the dead leaf stalk of an unidentified fern in a cloud forest in the state of Veracruz, México, is described and illustrated. This singular hyphomycete is distinguished from known genera by its euseptate, triangular or fusiform conidia which are attached at 90° to the long axis of the cicatrized conidiogenous cell.

Results of an investigation into the fungi associated with submerged wood in Lake Barrine, north Queensland, Australia are reported. Thirty-nine fungi were identified, 15 ascomycetes, 23 deuteromycetes and one basidiomycete. The frequency of occurrence and the effect of the incubation period on the recovery of fungi has also been investigated and is presented. The new species Massarina lunispora and Dactylaria lakebarrinensis, and some other notable species, are described and illustrated.

Filosporella pinguis sp. nov., Pachycladina parva sp. nov. and Pleuropedium macrum sp. nov. from stream foam collected in the catchment of the Miramichi River, New Brunswick, are described and illustrated. Filosporella pinguis has a microconidial state. Keys to species in the above genera are provided.

Endophytic fungi were isolated from nine plant species growing on gypsum and saline soils in central Spain. The plants sampled were Arundo donax, Atriplex halimus, Diplotaxis erucoides, Ephedra nebrodensis, Phragmites australis, Rosmarinus officinalis, Scirpus holoschoenus, S. maritimus and Stipa tenacissima. A total of 152 fungal species were recovered from 2880 samples of leaves, stems or twigs, taken from 45 individual plants. Ephedra and Rosmarinus showed the highest diversity of endophytes, whereas both species of Scirpus showed the lowest. The most frequently isolated fungi were Alternaria alternata, Sporormiella intermedia, Rhizoctonia sp., Epicoccum purpurascens, Pleospora herbarum, Cladosporium herbarum, Sporormiella australis and a sterile fungus. A total of 187 strains belonging to 136 species were tested for the production of antimicrobial activities, using a panel of bacteria and yeasts, some of them of clinical relevance. Production of antimicrobial compounds was detected in 45 strains, belonging to 37 species. Large differences were observed among isolates from the same species, with respect to their ability to produce metabolites with antimicrobial activity.

Internally transcribed spacer (ITS) regions of the rRNA gene cluster in isolates of Ascochyta spp. were amplified and digested with restriction endonucleases. Addition of fragment sizes from conventional gel electrophoresis gave anomalous sizes which suggested the presence of more than one PCR product. Separation in HA-Yellow containing agarose gel allowed the detection of fragments of the same size but with different sequences. Isolates of Ascochyta spp. were shown to possess multiple PCR-amplification products of the same sizes, but with significant sequence differences.

As one of the endangered breed of mycologists to have maintained an interest in oomycetes, I am compelled to defend the rationale in continuing to refer to these micro-organisms as fungi. This paper is stimulated by recent communications in which my mycological colleagues have, with apparent relish, pointed to what they perceive as inaccurate references to oomycetes as fungi. David Moore (1997) provides a prime example in his review of The Growing Fungus edited by N. A. R. Gow & G. M. Gadd (1995). Moore criticizes the editors for allowing so many pages of their book to be devoted to these micro-organisms, when ‘…Neurospora is probably more closely related to a cow's nose than it is to Saprolegnia’. While a phylogenetic chasm separates the oomycetes from other fungi, I shall argue that it is impractical to restrict the usage of the term fungus to those micro-organisms that qualify as members of the Phylum Fungi (Alexopoulos, Mims & Blackwell, 1996, provide a contemporary overview of fungal systematics). This argument should have been settled by a series of clear-sighted articles published after molecular genetic analyses confirmed the polyphyletic nature of the fungi (Christensen, 1990; Bruns, White & Taylor, 1991; Hawksworth, 1991; Barr, 1992). For example, Donald Barr (1992) suggested that oomycetes are fungi in the colloquial sense of the term and that it is the colloquial sense of the term that will continue to be most meaningful to mycologists. But since the message of these articles was apparently missed by many mycologists, I hope that this note will clarify a practical definition of the fungi that includes the oomycetes but which does not conflict with a natural classification of the Phylum Fungi that excludes them.