Lichens are typically formed by the association of two partners. The fungus (mycobiont) usually comprises most of the lichen, while the photosynthetic algal or cyanobacterial partner is referred to as the photobiont. Many lichens contain more than one photobiont and other associates, the lichenicolous fungi, may also be involved. The spectrum of interactions is fascinating and ranges from mutualism, through commensalism, to situations where one, or sometimes more, of the associates is doomed by the antagonistic activities of an invading fungus. Furthermore, these interactions are dynamic over time. Many mycologists assume that once a lichen ascospore has contacted a suitable photobiont, or once a dual propagule such as a soredium, isidium or lichen fragment has landed on an appropriate surface, a lichen thallus will develop. Accepted dogma is that the thallus will grow to form a mature lichen surviving for tens, if not hundreds or even thousands of years. These are over-simplifications; in fact there is war in the world of lichens. Following a brief consideration of parasitism and other forms of symbiosis, this war will be illustrated under the headings of algal slaves, exploiters of two kingdoms, alien invaders, cosy niche seekers and take-over specialists. It is hoped that this review will encourage mycologists to study these interactions which, as yet, remain largely unexplored.

A field study was carried out in a remote broadleaved Fagus longipetiolata forest in Shaanxi province, China to study the natural local distribution of Lentinula edodes. Following spatial mapping, 24 fruit bodies were collected for tissue isolation into axenic culture. 24 genets distributed on fallen tree trunks within a distance of 120 m were identified and clustered into 7 groups using the unweighted pair-group method algorithm using data based on colony morphologies, abilities to degrade aromatic poly-R478 dye, somatic incompatibility reaction patterns and DNA fingerprints. Among the parameters used, the somatic incompatibility reaction, a polygenic phenotype, was the most differentiating, identifying 22 incompatible classes. Two sets of fruit bodies of different genets were so close together that they would otherwise have been described as aggregate fruits of presumed identical origin. Eighteen genets found on the same 5.6 m long tree trunk divided roughly into two clusters, matching their spatial distribution, and a nearby branch bore another distinct cluster. More heterogeneity was encountered between isolates the greater the distance separating them on the original site. Genets on the same tree trunk showed more compatible somatic reactions among themselves, and their DNA fingerprints showed higher similarity. Nevertheless, considering the totality of phenotypic characters, each fruit body is a genet in L. edodes. Such features are concluded to result from a reproductive strategy which depends on basidiospore dispersal. Within each cluster of isolates from the collection site genets seemed to have arisen from multiple sib-mating events. Thus, a cluster may represent a lineage of L. edodes. Individualism in L. edodes is based on a strong somatic incompatibility system. Strong competition from contaminating individuals arriving as air-borne basidiospores could explain decreased and fluctuating crop yields which are now frequently observed in later flushes from the outdoor wood log cultivation system. Further, it would also explain why multispore spawn is not favoured in artificial cultivation of this economically important edible mushroom.

The macro- and micromorphology of 45 specimens and 19 holotypes of the subgenus Ganoderma (=G. lucidum complex) were examined, together with isoenzymic data. The objective was to evaluate relationships by analysing numerically morphological and isoenzymic data to discern the number of species occurring in southern South America, and their delimitation. A total of 73 isozymic bands and 26 morphological characters were considered. Spore ornamentation was studied under SEM. Nine taxa appear to be represented in the region (G. lucidum var. lucidum, G. multiplicatum, G. sessiliforme, G. praelongum, G. subincrustatum, G. platense, G. zonatum, G. sessile and G. tuberculosum) and the presence of another eight is doubtful (G. argillaceum, G. bibadiostraum, G. chaffangeonii, G. lucidum var. capense, G. lucidum var. dorsale, G. subamboinense var. laevisporum, G. resinaceum and G. tropicum). Three major cutis types were defined and illustrated. Although congruence between dendrograms derived from both data sets was low, some similar groupings were formed. Species descriptions and a key for identification are provided.

Ceriporiopsis microporus sp. nov. and Tyromyces formosanus sp. nov., found growing saprotrophically on the decayed stems of Chamaecyparis formosensis and unidentified hardwood, respectively, in Taiwan are described and illustrated. C. microporus is distinguished by small hymenial pores and broadly ellipsoid to subglobose basidiospores. T. formosanus is characterized by large, broadly ellipsoid to subglobose basidiospores. Cultural characteristics are described for the two species.

Morphological variation of germ tubes originating from aeciospores of Peridermium pini and Cronartium flaccidum populations on Pinus sylvestris was investigated in rust populations from Finland, the United Kingdom and Italy. The observed morphological variation was generally higher among than between these rust populations. The variation in germ tube length of the rust samples was high over the incubation period. Peridermium pini could not be distinguished from C. flaccidum based on its germ tube morphology.

Protoplasts of Choanephora cucurbitarum were obtained by treatment of germlings with commercial enzymes. Colonies originated from regenerated protoplasts showed the same mating type and colony type as their respective parent. Colonies from fused protoplasts of two (+) isolates were of the (+) type, while those from two (−) isolates were of the (−) type. Colonies derived from fused protoplasts of (+) and (−) isolates were self-fertile and produced azygospores and zygospores subsequently. This result supports the hypothesis that azygospores of C. cucurbitarum are single-suspensor zygospores. Mating type heterokaryons resulting from fused protoplasts of (+) and (−) isolates with different colony types segregated into component isolates indicating that karyogamy and meiosis did not occur.

Coniochaeta rhopalochaeta sp. nov. was isolated from decorticated wood of Bulnesia retama in Argentina. It is distinguished principally by the ascomata with mace-like capitate setae. C. scatigena is first recorded for Argentina. A key to the seven known Argentine species of Coniochaeta is provided. Asci of these species were studied with fluorescence microscopy; size of the fluorescent apical ring could be a useful taxonomic character.

Five lignicolous mangrove fungi (Hypoxlon oceanicum, Julella avicenniae, Lignincola laevis, Savoryella lignicola and Trematosphaeria mangrovei) produced extracellular endoglucanase, cellobiohydrolase and β-glucosidase when cultivated under static conditions in a defined liquid growth medium. Agitation of cultures completely repressed enzyme production. Cellulase production by H. oceanicum was 2–5 fold higher compared to other strains. Increasing salinity generally resulted in reduced enzyme production although responses varied, but J. avicenniae appeared relatively unaffected by salinity within the range 0–3·4%.

Mass mortality among pond cultured red drum (Sciaenops ocellatus) was observed in Hong Kong. Affected fish were lethargic and lost their appetite but no lesions on the body surface were apparent. Patches of white to brownish cottony growth on the gills of affected fish were observed and microscopic examination revealed mats of hyaline mycelia with mature zoosporangia and oogonia which were identified as Saprolegnia diclina. During induced sporulation, production of primary and secondary zoospores, oogonia, and antheridia were observed. A physiological study of the growth and sporulation of a representative isolate determined its optimum growth requirements. The isolate can grow from pH 4 to 10, in distilled water, at salinities of 5–30‰, and temperatures of 4–30°. Maximum growth was observed at pH 5 and 8–10, at salinities of 5–10‰, and 25–30°. Production of zoosporangia only occurred in distilled water, 5 and 10‰ salinities, with zoospores released in distilled water and 5‰ salinity. Zoospore release was also observed from 4 to 30° with greater abundance at 25 and 30°, while oogonia and antheridia were produced in distilled water and from 5 to 30‰ salinities and at 20–30°.

Strains of Hebeloma representative of different climatic zones were grown in axenic culture at either 2°C and 22° or 6° and 22°. Culture filtrates were assayed for proteolytic activity using FITC labelled BSA as a substrate. Assays were run between 0–37°. Growth at low temperature induced greater proteolytic activity (g−1D.W. mycelium). Many of the strains produced protease(s) which retained significant activity at temperatures as low as 0°, and a thermal optimum between 0–6° with a second optimum at higher temperature. The results are discussed in relation the nutrient acquisition potential of ectomycorrhizal fungi at low temperature and the contribution such cold active proteases might make to the soil enzyme pool.

Puccinia recondita f. sp. tritici pathotype (pt) 64-(6),(7),(10),11 was first detected in Australia in northern New South Wales in 1990. Greenhouse tests of pathogenicity on wheat and triticale genotypes indicated that this pathotype was similar to two closely related pathotypes, but differed from them in at least three pathogenic features indicating that it had not arisen by a simple mutational event. Pathotype 64-(6),(7),(10),11 combined several pathogenic and isozymic features which, prior to its detection, were known only in two different groups of pathotypes, strongly suggesting that it had arisen via somatic hybridisation between isolates from each group. This hypothesis was supported by the RAPD phenotypes of isolates representing pathotypes present in Australia at the time pt 64-(6),(7),(10),11 was first detected. The hybrid pathotype combined virulence for Lr1 with partial virulence for gene Lr13 and was fully virulent in greenhouse adult plant tests on two hybrid wheats heterozygous for these genes. This is the first case where compelling evidence has been obtained for somatic hybridization in Prt and only the second of inter pathotype somatic hybridization in a wheat rust under field conditions.

The succession of microfungal communities on Myrtus communis leaf litter was monitored from Jan. 1993 to Nov. 1994 using the litter bag method. Three main groups of fungal colonizers were identified, whose presence is correlated with the successive decomposition stages of the substrate and with seasonal variations.

A new freshwater ascomycete Micropeltopsis quinquecladiopsis sp. nov. was collected on submerged twigs in a stream in Thailand. The fungus is described at the light microscope, scanning and transmission electron microscope level. Distinctive features are the appendaged 1-septate hyaline ascospores. The appendage arises as an outgrowth of the episporium from a basal stalk, then divides into five arms (three long and two short). The episporium and appendages are surrounded by an indistinct (at light microscope level) mucilaginous layer. The fungus is assigned to the Dothideales (Trichothyriaceae). Ascospore appendage ontogeny is compared with those of marine Ascomycota (Halosphaeriales).

Spores of Tetrachaetum elegans were isolated in early autumn from submerged leaves which were randomly collected at a single site from a small stream in southwestern France. In order to investigate potential substrate preferences, spores were sampled in four leaves from seven different plant genera. A total of 96 monosporic isolates were screened for genetic variation in RAPD patterns using nine different primers. Fifty-two fragments were identified and used for calculation of similarity coefficients. A large number of fragments were shared across all isolates, suggesting that the population was genetically homogeneous. The combination of 11 polymorphic fragments contributed to the delineation of 13 RAPD types. Colonization of a single leaf by multiple genotypes was frequently encountered. Fungal genetic assemblages differed between plant genera. Variations in the frequency of occurrence of the various genotypes are discussed in terms of ecological strategies and in reference to previous work at the community level. We suggested two hypotheses: first, substrate preferences are found among aquatic hyphomycete genotypes, and secondly, sequential occupation by distinctive populations may result in different assortments of genotypes on leaf litters of different plants at any given time of sampling.

Most species of Ceratocystis sensu stricto are virulent pathogens of a wide variety of plants including forest and fruit trees, sweet potato, pineapple and sugar cane. Confusion exists regarding the taxonomy of the species in this genus. The aim of this study was to develop a rapid and reliable PCR-based RFLP identification method and to consider phylogenetic relationships among the better-known species of Ceratocystis. A 1·6 kb fragment within the ribosomal DNA operon was directly amplified from living fungal tissue, without extracting DNA. The amplified fragment included part of the small (SSU) and large (LSU) sub-unit rRNA genes, the 5·8S rRNA gene and the internal transcribed spacers (ITS) 1 and 2. The PCR fragments were digested with eighteen restriction enzymes. Four of these (Alu I, Dra I, Hae III and Rsa I) produced RFLPs that separated the species of Ceratocystis. The amplification products from the best-known species were sequenced, and the delimitation of taxa based on this phylogenetic analysis generally agreed with results of previous studies using isozymes and rDNA sequence analysis. This study provides an extended understanding of the relationships among species of Ceratocystis and will form a sound foundation for further taxonomic studies of the group.

Changes caused by Septoria apiicola during the development of leaf spot disease in celery were quantified stereologically in susceptible cvs, a partially resistant parental wild celery line, fully resistant parsley and lovage. Thick sections, cut in vertical orientation, were stained and using a camera lucida, were superimposed on a lattice grid for stereological analysis. The volume of each component within the leaf space was calculated using the Cavalieri method.

In healthy tissue volume fractions of intercellular space, palisade layers and, to a lesser extent, collenchyma, vascular tissue and oil ducts were greater in the more resistant genotypes. This coincided with a reduction in the volume fraction of mesophyll tissue. Estimates of absolute volume fraction were similar. In both resistant and susceptible celery the principal response to infection was a substantial decrease in the volume fractions and absolute volumes of palisade and mesophyll tissue. Volume fractions of mesophyll and palisade tissues declined by 97% in susceptible lesions and by 98% in resistant lesions. The fungus was not observed in xylem or phloem cells. No appreciable changes were observed in either collenchyma or oil duct tissues in response to infection in resistant and susceptible genotypes. Infection had no effect on the epidermis or stomata and these remained intact until late in the infection cycle, when pycnidia erupted through the epidermis of the upper and lower leaf surfaces.

No hyphae were found in leaf sections of lovage or parsley, and fungal growth was severely restricted in all resistant material bred from wild celery. In wild celery lines, S. apiicola did not produce any, or produced very few, pycnidia and the volume fraction of vegetative hyphae was lower than that in susceptible cvs, where the fungus proliferated extensively within the lesions and many pycnidia were produced. This accounted for 30–50% of the fungal material in lesions on susceptible celery plants. The amount of fungus (21%) was less in lesions on resistant celery and in this material 96% of the fungus was present as vegetative hyphae. In lesions formed on susceptible celery 26% of the fungal tissue was reproductive and of that 11% was conidia whereas in resistant celery, where pycnidia were present, these structures were morphologically abnormal and did not contain conidia. Stereological analysis demonstrated clear differences in plant and pathogen response during infection of resistant and susceptible celery by S. apiicola.

A new staining method for the examination of active regions of hyphae is presented. Using a simple protocol, application of the fluorescent stain Mag fura (tetra-potassium salt) in low pH buffer to two filamentous fungi resulted in bright responses to active hyphal regions. Not only were active apices delineated, but more distal compartments were also found to respond to the stain. Some apices did not stain, presumably because they were inactive. It is believed that all stained regions retained cell membrane integrity and are thought to have had high membrane ATPase activity. All showed high nuclear and mitochondrial complements. The stain was apparently held within the cell wall structure, close to the cell membrane. It is hypothesized that it was responding to a localized flux of divalent cations from the cell membrane. With non-active regions, only a low level of response to the stain remained, at the exterior of the cell wall. This low emission is thought to be a response to contaminating ions in the buffer. It could be clearly distinguished from the bright response associated with the active regions. Counter-staining with other commonly used fluorescent probes showed these regions of low response (unless they were completely degenerated) still contained nuclear material and mitochondria.

The fluorescent signal from active regions of fungal hyphae was sufficiently bright and persistent for visualization by a conventional CCD camera. This will allow the development of image analysis protocols to measure the effects of environmental conditions on fungal physiology, using commonly available equipment.

A new nematophagous hyphomycete is described from the Canary Islands as Arthrobotrys hertziana. It has branched conidiophores with slightly swollen tips, mostly three-septate conidia, and sticky knobs as trapping devices. A key to Arthrobotrys species forming sticky knobs is presented. Among six nematode and two springtail species tested as hosts only the nematode Panagrellus redivivus was trapped. The results are discussed with reference to taxonomical problems and the possibly limited host range.

The patterns of mycelial development (length and branching) of five strains of Fusarium oxysporum were measured in the vicinity of tomato and wheat roots. Two strains were of f. sp. lycopersici, two of f. sp. radicis-lycopersici and the fifth was a non-pathogenic strain currently used as a biocontrol agent. Hyphal extension and branching were measured microscopically using a CCD camera and an image analyser. Furthermore, the role of soluble root exudates, insoluble root materials, glucose supply, and nitrogen supply (casamino acids) on mycelial development was investigated. Each strain had its own pattern of development in the absence of a root. Fungal development of all five strains was stimulated in the vicinity of roots irrespective of plant species but there was no chemotropic response towards or away from the root. Both pathogenic and non-pathogenic F. oxysporum populations exhibited their own characteristic growth and development features which were not related to their pathogenicity. Growth stimulation was mainly related to the presence of organic nitrogen in the soluble exudates. It is proposed that signalling and recognition mechanisms between the host plant and the pathogenic or non-pathogenic strains are likely to occur on or in the root rather than external to the root.

Primordia formation and basidiocarp maturation have separate requirements for light. Both show maximum activity in the 440–470 nm range but with slightly different peak values. Maturation requires over 2 orders of magnitude longer exposures to light than does initiation. Fluence–response relationships of primordia initiation are complex and do not show reciprocity.