J. Webster

Aquatic hyphomycete spora of the River Exe and its tributaries

Water samples collected from the River Exe and its tributaries at weekly intervals during the period August 1970 to September 1971 were filtered through Millipore filters which were then stained to show the spores of aquatic hyphomycetes. Quantitative estimates of the spore content of the water are presented, and attempts are made to relate the concentration of particular species to such variables as the rate of leaf fall into the rivers, water temperature and pH.

An experimental analysis of the coprophilous fungus succession

A quantitative method for following the succession of fungus fruit bodies on rabbit pellets is described. Comparison of latent periods for spore germination (following alkaline pancreatin treatment) and rates of germ tube extension showed no correlation with the observed time of appearance of fruit bodies. Under a variety of conditions several fungi showed a characteristic minimum time of fruit body appearance which corresponded closely to the observed successional sequence. Evidence was obtained that Coprinus heptemerus was antagonistic to and limited the fruiting of Pilaira anomala, Pilobolus crystallinus and Ascobolus viridulus. No evidence for bacterial antagonism or for nutrient depletion as factors limiting the fruiting of P. crystallinus was obtained.

Antagonism between Coprinus heptemerus and other coprophilous fungi

The effect of Coprinus heptemerus M. Lange & A. H. Smith on the sporulation of Pilobolus crystallinus (Wiggers) Tode and Ascobolus crenulatus Karst, was studied on both sterilized rabbit dung-pellets and on pellets obtained from rabbits fed with sterilized food sprayed with spores. The results obtained confirm those of Harper & Webster (1964) who found that the presence of C. heptemerus within a rabbit pellet is associated with marked depression of fruiting of P. crystallinus and A. crenulatus , and suggest that the antagonism occurs under natural conditions. Studies on rabbit pellets and agar plates indicate that the suppression of fruiting of P. crystallinus and A. crenulatus by C. heptemerus is by hyphal interference, a mode of antagonism which operates on contact or at close proximity to the hyphae of the antagonist. The principal effect of the hyphal-interference factor appears to be a drastic alteration of the permeability of the cell membrane leading to the death of the cell. The intracellular changes accompanying the hyphal interference by C. heptemerus were studied in A. crenulatus . These include loss of hydrostatic pressure, vacuolation and granulation of the cytoplasm. A preliminary investigation was made on the nutritional relationships between C. heptemerus and A. crenulatus . No evidence was obtained that the former derives nutrients from the affected cells of the latter.

Hyphal interference in a range of coprophilous fungi

A range of coprophilous and some non-coprophilous fungi has been examined for ability to cause hyphal interference and for sensitivity to it. The results suggest that sensitivity to the hyphal interference of Coprinus heptemerus is widespread among coprophilous fungi and that many non-coprophilous species may also be sensitive. Ability to show hyphal interference is not only common among coprophilous basidiomycetes but is also found in those belonging to other ecological groups. Coprophilous basidiomycetes show interference against one another.

Critique of the chitin assay technique for estimation of fungal biomass

Colorimetric determination of chitin content of nine aero-aquatic hyphomycetes showed that the conversion factor (CF) values (chitin content per unit dry weight of mycelium) varied with the age of mycelium, nutrient content of the medium, and initial oxygen concentration of the water. CF values often decreased with age of mycelium and also with lowered oxygen concentrations. Consequently, for estimation of fungal biomass in tissues, this technique is of limited value.

The trapping of aquatic hyphomycete spores by air bubbles

A technique is described for estimating the rate of removal of aquatic hyphomycete spores from suspension by air bubbles, and for calculating the trapping efficiency of an air bubble. Values for trapping efficiency are given for different kinds of hyphomycete spore. In general, the branched type of spore is more readily removed from suspension than spores of conventional shape, although the trapping of the sigmoid spores of Anguillospora crassa is quite effective. Evidence is presented for Varicosporium elodeae that as the complexity of branching of the spore increases, the effectiveness of trapping by air bubbles also increases. The addition of detergent causes an increase in the rate of removal of spores.

Aquatic hyphomycete communities in the River Teign I. Longitudinal distribution patterns

The aquatic hyphomycete community in the River Teign was sampled by the filtration of water, leaf pack baiting and examination of naturally occurring substrata. Fifty-two species (exclusive of five unidentifiable forms) were found. The community at Site I (Walla Brook, a moorland stream) was distinctly different from two downstream communities. At Site I there were fewer species, fewer conidia l −1 , and lower numbers of species per unit area of leaf. Fewer than 20 % of all species actually seen developing on leaves occurred at all three sites; most species occurred at both Sites II and III. Clavatospora longibrachiata was the only species dominant at all three sites throughout the study.

Aquatic hyphomycete spora of some Dartmoor streams

Changes in the aquatic hyphomycete spore content of three Dartmoor streams were followed throughout a 15-month period by Millipore nitration. Despite the fact that two of the rivers are not surrounded by deciduous trees, they contain a flora of aquatic hyphomycetes, including a number of distinctive forms which grow on Juncus and grass debris.

Ballistospore discharge in Itersonilia perplexans

Ballistospore discharge in Itersonilia perplexans is described. Evidence is presented that a drop of liquid, and not a gas bubble, develops at the hilar appendix immediately before discharge. Spores detached on a micromanipulator needle produce liquid drops. The trajectories of several spores have been plotted. The horizontal and vertical distances of discharge have been measured, and the terminal velocity of sedimentation. From these values, the initial discharge velocity has been estimated at 5.5 m s−1. Evidence is presented that discharged spores carry a negative electrical charge. Two possible mechanisms for spore projection are discussed, a rapid transference of the centre of mass of the spore associated with wetting, and a change in the electrical charge on the spore surface at wetting, followed by electrostatic repulsion.

Anaerobic survival of aquatic fungi

Aero-aquatic Hyphomycetes were tested for their ability to survive on beech leaf disks under anaerobic conditions for periods of up to 12 months. Helicodendron triglitziense, H. conglomeration and H. giganteum showed 100% survival, while H. luteo-album and H. hyalinum showed reduced survival. Survival of aero-aquatic Hyphomycetes, Ingoldian aquatic Hyphomycetes and members of the Saprolegniales was also compared on hemp seeds under anaerobic conditions. Aero-aquatic Hyphomycetes showed the greatest percentage survival. Articulospora tetracladia, Achlya colorata (isolate lacking oospores) and Dictyuchus sterilis failed to survive even 3 months. No significant difference was found in the survival of Tricladium splendens from a stagnant drainage ditch and from a fast-flowing river. Only species of Saprolegniales with oospores survived anaerobic conditions.