Botanical Journal of the Linnean Socic!y (1985), 91: 45-50. With 10 figures
Morning dew and Tripospermum
(Hyphomycetes)
KEISUKE TUBAKI, SEIJI TOKUMASU AND KATSUHIKO ANDO*
Institute of Biological Sciences, Universily of Tsukuba, Niihari-gun,
Sakura-mura, Ibaraki, 305 Japan
Received November 1984, accepted for publication February 1985
TUBAKI, K., TOKUMASU, S. & ANDO, K. 1985. Morning dew and Tripsparmum
(Hyphomycetes).Morning dew appears to be a n important factor in the habitat of Tripospermum
species. I t affects both conidial development and liberation.
ADDITIONAL KEY WORDS:-Conidial
release
-
germination.
CONTENTS
Introduction . . . .
Methods and observations .
Discussion. . . . .
Acknowledgement.
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References.
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INTRODUCTION
Among the most interesting biotopes for aquatic fungi are the small
temporary bodies of water in forests. Some of these are small pools that
gradually recede during the dry season and, in the last stages of the drying
process, consist only of thin films of water. Numerous fungi start to sporulate
under these conditions, their spores being floated free by any new input of
water. The spores are mostly conidia of the aero-aquatic hyphomycetes. Dew,
studied here, can be considered the smallest extreme in temporary bodies of
water in forests. It is felt that dew should be taken into account as an important
factor in modification of some terrestrial habitats in making them suitable for
some ‘aquatic’ hyphomycetes.
Dew falls on leaf surfaces at a variable time after dusk until early morning;
leaf surfaces are thus wetted by presumably well-aerated water. Although the
amount of water involved is small, it often occurs in a regular, cyclic pattern
and should be sufficient for growth and sporulation of many microfungi on
leaves. Dew evaporates during the day and may be replaced the following night.
Present address: Tokyo Research Laboratory, Kyowa Hakko Co., 3-6-6 Asahi-machi, Machida-shi, Tokyo
194, Japan.
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0 1985 The Linnean Society of London
00244074/85/050045 06 $03.00/0
+
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K. TUBAKI ET AL.
During the period for which they exist, the water films could contain dissolved
nutrients sufficient for growth and sporulation of aquatic and aero-aquatic
hyphomycetes. This hypothesis led us to search for conidia of such fungi in dew
collected in the field.
METHODS AND OBSERVATIONS
In the summer of 1980, samples of dew that accumulated on the surfaces of
leaves at the Sugadaira Montane Research Centre of the University of Tsukuba,
Sugadaira Heights, Nagano Prefecture were examined. The area, well-known
for fog, is situated 380 m above sea level in central Honshuu, Japan. Dew was
collected from leaves of Miscanlhus sinensis Anders each morning for 1 week.
Several cubic centimeters of dew were easily obtained by spreading a clean
polyethylene sheet ( 1 m 2 ) on the ground, then tapping leaves gently above the
sheet. The accumulated water was placed in tubes, returned to the laboratory,
Figures 1-7. Conidia in dew samples. Figs 1-3. Conidia of aquatic hyphomycetes. Bar = 10 pm.
Figs 4-7. Conidia of Tn)os/mnum species in different stages of development. Bar = 20 pm.
MORNING DEW AND TRIPOSPERMUM
41
and allowed to settle; FAA fixative was used to preserve the samples.
Subsequently, the samples were examined microscopically and found to contain
conidia of well-known aquatic hyphomycetes such as species of Articulospora,
Lateriramulosa and Trinacrium (Fig. 1 ). This substantiated reports by Bandoni
(1972, 1975, 1981) and others of the occurrence of aquatic hyphomycetes in
terrestrial habitats.
Interesting conidia of other taxa were present in the dew, including some
obviously belonging to species of Tripospermum. These conidia (Figs 4,5) were in
different stages of development, some being immature, some three-armed, and
others fully mature. Such conidia were found not only in dew samples from
Miscanthus sinensis, but from those collected on leaves of various species Quercus,
Magnolia, and other shrubs. Figure 8 illustrates the presence of both conidia and
hyphae on the surface of a living Miscanthus sinensis leaf. Consistent presence of
conidia of this group in the samples suggests that heavy dew might be important
in both development and release of these propagules.
Tripospermum is a well-known hyphomycete genus, the species of which are
characterized by dark staurospores of unusual form; they are common on fallen
Figure 8. S C M of the upper surface of living leaf of M . sinensis, showing the presence of conidia and
hyphae of Tripospcrrnurn species. Bar = 50 pm.
48
K . TUBAKI E T AL.
leaves and in foam or scum on streams. Hudson & Sutton (1964) found conidia
of T. myrti (Lind) Hughes in wash water used to clean deciduous tree leaves.
Jones ( 1976) listed this species among aquatic hyphomycetes reported from
terrestrial habitats. Most species of the genus sporulate readily on laboratory
media and, since they are known to occur on living leaves, are obviously
foliicolous rather than aquatic. However, because of the regular deposition of
dew on leaves where such fungi grow, their habitat can be considered as
alternating between ‘terrestrial’ and ‘aquatic’. If conidial development is related
to the presence of dew, then such conidia would have to develop in a rather
short period. T o test this ability, the following laboratory experiments were
carried out.
Monoconidial isolates of four Tripospermum species were obtained using the
method described by Ando & Tubaki (1984). The four, obtained from dew
samples from Miscanthus sinensis, were T. acerinum (Sydow) Speg., T. camelopardus
Ingold, 7.myri, and T. prolongatum Sinclair & Morgan-Jones. These isolates
grew and sporulated readily at room temperature on commonly available agars
such as malt extract agar, potato dextrose agar and cornmeal agar. Where
drops of condensed water touched a colony, sporulation was strongly stimulated
(Figs 9, 10). T o determine the effect of water drops on sporulation, plain agar
plates were inoculated centrally with a strain of 1.acerinum, then incubated at
20°C until the colony diameter reached c. 5 mm. Subsequently, one drop of
distilled water (0.035 cm3) was allowed to fall (height c. 5 mm) on the margin of
the colony at each of two opposite points. Cultures were then incubated for
24 h, after which 10 x 20 mm blocks of the wetted colony areas were removed
and placed on sterile slides. Under low-power magnification ( x 100) the
number of conidia present on each block was counted. Mean counts were made
from four replicates of this procedure and the results are: colonies with water
drop, 1025 conidia; colonies without water drop, 518 conidia.
Water drops were again dispensed on portions of colonies where conidia had
developed abundantly. This water was immediately removed and examincd
Figures 9-10, Development of condia of T. acerinum on a colony with (Fig. 9) and without (Fig. 10)
added water drops. Bar = 10 prn.
MORNING DEW A N D TRRIPOSPERMUM
49
microscopically for the presence of conidia. The water drops were found to be
effective in liberating conidia, causing release of propagules in all stages of
development. T h e appearance of these samples was identical to that observed in
naturally occurring dew samples. This suggests that conidia are weakly attached
and are consequently separated relatively easily from the conidiophores. T h e
conidial shape is such that the surface area to volume ratio is high, and surface
tension forces of water droplets applied against this surface are sufficient to
remove conidia from their conidiophores. Similar observations have been made
with conidia of Ingoldiella hamata Shaw (Shaw, 1972). After release, the conidia
float free and can be dispersed by water movement. Intermittent wetting can
thus be effective in conidial release as well as in providing the water necessary
for growth of the mycelium.
DISCUSSION
Morning dew seems to be an important part of the habitat for species of
Tripospermum and other leaf-inhabiting fungi from the standpoint of conidial
development and liberation. The involvement in liberation explains the
abundance of Tripospermum conidia in dew on leaves.
It is speculated that conidia of Tripospermum species germinate readily in dew,
or where humidity is suitable, on leaves. Continued growth of the hyphae is
probably correlated with the nocturnal presence of dew, stopping during the
daily dry periods. Conidial primordia and conidia are eventually formed to be
liberated when dew is again present or when wet by rain. Conidial counts from
wetted and control colonies demonstrated strong stimulation of sporulation in
7.acerinum following wetting.
In Tripospermum the mature staurospores consist of a stalk and two pairs of
divergent, septate, pointed arms; the branches are not formed simultaneously.
When conidia of this kind germinate, germ tubes can be produced from any of
the numerous cells; this occurs whether the conidia are mature or immature.
Therefore, conidial age at release is not an important consideration as all
conidia are capable of propagating the species. T h a t is, release of partially
developed conidia does not appear to be disadvantageous.
The presence of various stages in development of conidia in samples liberated
from a single Tripospermum species is of taxonomic interest. Since such conidia
differ markedly in shape and size, it is essential that species of the genus are
separated only after careful cultural observations. This precautionary approach
is also necessary with species of aquatic hyphomycetes in which remarkably
variable conidia are known.
ACKNOWLEDGEMENT
We thank Dr R. J . Bandoni, University of British Columbia, for his kind
suggestions and for reviewing the manuscript.
REFERENCES
ANDO, K.& ‘I‘UBAKI, K . , 1984. Some undescribed hyphornycetes in the rain drops from intact leafsurfare.
Transactions of the Japanese Mycological Socicp, 25: 2 1-3 7.
BANDONI, R. J., 1972. Terrestrial occurrence of some aquatic hyphomycetes. Canadian Journal of Botany, 50:
zzn3-228n.
50
K. TUBAKI E T AL.
BANDONI, R. J., 1975. Significance of the tetraradiate form in dispersal of terrestrial fungi. Repor! oJ the
7ottori Mycological Institute, 12: 105-1 13.
BANDONI, R . J., 1981. Aquatic hyphomycetes in terrestrial litter. I n D. T. Wicklow & G. C. Carroll (Eds),
The Fungal CommuniQ: 693-703. New York: Dekker.
HUDSON, H. J. & SUTTON, B. C., 1964. Trisulcosporium and Tctranacrium, two new genera of Fungi
Imperfecti. Transadions of the British Mycological Socicg, 47: 197-203.
JONES, E. B. G . , 1976. Topics of further interest. In E. B. G . Jones (Ed.), Reccnl Aduances in Aqualic Mycology:
707-724. London: ELEK Science.
SHAW, D. E., 1972. Ingoldiclla hamata, gen. et sp. nov., a fungus with clamp connections from a stream in
North Queensland. Transactions oJ the British Mycological Socieg, 59: 255-259.