Institute of Botany
Mag. Gerfried Deutsch
fungi of terrestrial orchids
orchids with endophytic fungi is essential in many cases for seed germination
and subsequent plant development.
It has been observed
that, in addition to phosphate and other minerals, the associated fungus
provides the tiny seeds with a carbon source, as well as with vitamins
and growth factors.
The balance between
orchids and their endophytes in a mycorrhizal association is very delicate
and often too much nutrition in in vitro cultures has an adverce effect
on the seeds or seedlings, in many cases they are even killed by the fungus.
associated with green (assimilating) orchids belong to the sub-division
Basidiomycotina, class Hymenomycetes, form genus Rhizoctonia.
techniques are based on number of nuclei per hyphal cell, hyphal anastomosis,
cytomorphologyof hxphae and the morphology of cultures.
Isolates of Rhizoctonia
possess the following characteristics:
near the distal septum of cells in young vegetative hyphae
of hyphae and formation of septa a short distance from the point of origin
of hyphal branches.
clamp connections, conidia, rhizomorphs and sklerotia differentiated into
rind and medulla.
There is usually
a clear distinction between the long straight main hyphae and short lateral
hyphae that branch repeatedly and form chains of moniloid cells. Another
charakteristic of many of these mycelia is, that in pure culture some hyphal
tips coil into peloton-like structures almost they do within the orchid
It is usually
difficult to match sterile mycelia with corresponding reproductive mycelia
(teleomorphs), but when the formation of reproductive organs is occasionally
induced in vitro, they can be identified as teleomorpic taxa. In this way
Rhizoctonia strains have been referred to a number of teleomorphic
genera and among those associated with orchids several have been referred
to species within Tulasnella, Sebacina, Ceratobasidium and Thanatephorus.
calospora and Ceratobasidium cornigerum are the most common
orchid endophytes. Strains referred to this fungi have establisched seedling
mycorrhiza with several orchids from Europe and Australia in vitro.
are isolated from the roots or rarely from the protocorms of terrestrial
orchids. Roots are first washed in water to remove most external debris
and then cut in longitudinal sections. Under a microscope individual
hyphal coils (pelotons) are teased from the tissue with the aid of fine
needles, placed into FIM-medium
and subcultured until free from contamination.
F. 1990. A study of hyphal morphology in the form genus Rhizoctonia.
- Mycotaxon 37: 25 - 46.
T. F. 1996. A comparative taxonomic study of Rhizoctonia
sensu lato employing morphological, ultrastructural and molecular methods.-
Mycol. Res. 100(9): 1117 - 1128.
J, PEGG G.F 1981. A technique for the establishment of mycorrhizal
infection in orchid tissue grown in aseptic culture. - New Phytol. 87:527
M., JABAJI - HARE S. H., CHAMBERLAND H. & CHAREST P. M. 1996.
Cytochemical and immunochemical investigation of the mycoparasitic interaction
between Stachybotrys elegans and ist host Rhizoctonia solani
(AG - 3).- Mycol.Res. 100(1): 79 - 86.
BURPEE L. & OGOSHI A. 1991. Identification of Rhizoctonia species
- The American Phytopathological Society, St. Paul, Minnesota, USA.
TU C. C.,
KIMBROUGH J. W. 1973. A rapid staining technique for Rhizoctonia solani
and related fungi. - Mycologia 65: 941 - 944
TU C. C.,
KIMBROUGH J. W. 1978. Systematics and Phylogeny of fungi in the Rhizoctonia
Complex. - Bot. Gaz. 139 (4): 454 - 466.
1983. Zu Problemen der Mykorrhiza bei Orchideen.- Mitt. Arb. Kr.
Heim. Orchid. DDR 12: 9 - 31.
J. H. 1985. Rhizanthella gardneri (Orchidaceae), its Rhizoctonia
Endophyte and close Association with Melaleuca uncinata (Myrtaceae)
in Western Australia.- New Phytol. 99: 273 - 280.
J. H., TALBOT P. H. B. 1971 Perfect states of Rhizoctonias
associated with orchids. I. - New Phytol. 70: 35 - 40.
J. H., TALBOT P. H. B. 1980. Perfect states of Rhizoctonias
associated with orchids. II. - New Phytol. 66: 631 - 641.
J. H., TALBOT P. H. B. 1980. Perfect states of Rhizoctonias associated
with orchids. III. - New Phytol. 86: 267 - 272.
J.H. 1975. Factors affecting symbiotic germination of orchid seed
- In SANDERS.F.E., MOSSE B.& TINKER P.B. 1975 Endomycorrhizas - Academic
J. H. 1971. Specificity of mycorrhizal Association in some Australian terrestrial
orchids - New Phytol. 70: 41 - 46
C. D., CURRAH R. S. 1995. Ceratorhiza pernacatena and Epulorhiza
calendulina spp. nov.: mycorrhizal fungi of terrestrial orchids. -
Can J. Bot. 73: 1981 - 1985.
C. D., CURRAH R. S. 1995. Evidence for a fungal liaison between Corallarhiza
trifida (Orchidaceae) and Pinus contorta (Pinaceae). - Can J.
Bot. 73:862 - 866.