Rhizoctonia repens

Etymology: The specific epithet repens means "creeping".

Synonyma:

Orcheomyces araniferae

1909

Ophrys

araniferae

1911

araniferae

1911

Orcheomyces bractescentis

1909

bractescentis

1911

Orcheomyces Harrisian

1909

Harrisiani

1911

Orcheomyces linguae

Serapias

linguae

1911

Orcheomyces psychodis

Habenaria

psychodis

1911

Paphiopedilum

Charlesworthii

1936

Arachnis

flos-aëris

Taeniophyllum

Hasselti

Dendrobium

crumenati

Cymbidium

sigmatoidei

Cymbidium

lancifolii

Nervilia

aragonae

Cryptostylis

arachnitis

Paphiopedilum

Argi

Cattleya

mossiae

Mossiae

1936

"Isoliert aus Laelio-Cattleya, Laelia, Spiranthes, diversen tropischen Cypripedien, Cymbidium Lowianum, Aërides maculosum, Bletilla und Coelogyne massangeana. Es besten Unterschiede zwischen den einzelnen formen der Dichte des Wuchses."

The first isolate came from a Laeliocattleya X 'Canhamiana'. The text continues as:

"Rhizoctonia repens ist, wie sofort zu sehen identisch mit unserer ersten Gruppe des Typus Psychodis. B e r n a r d hat verschiedene Formen dieser ersten, anscheinend weit verbreiteten Gruppe unter die eine Bezeichnung gebracht. Auch Pilze unserer zweiten Gruppe des Typus Apiferae können hierher gehören, so z. B. die aus Ophrys fusca und O. aranifera R. isolierten."

M. R. psychodis Burgeff (1936., p. 129, Fig. 116)
14 days old culture on 0,05% starch agar

M. R. psychodis Burgeff (1936., p. 129, Fig. 117)
6 weeks old culture on 2% starch agar

Telophase: Tulasnella calospora (Boudier) Jouel

Diagnosis

"Mycelium toujours rampant, formant sur les milieux nutritifs riches un voile épais, blanc jaunatre, qui peut devenir brun clair tardivement. Filaments moniliformes ramifiés, groupés en petits amas granuleux, jamais anastomosés. Pelotons formés par l'enroulement de filaments mycéliens sur eux-memes pendant de nombreux tours." (Quoted after Burgeff 1909., p.209)

Bernard (1909.)

"Deutlich geht die Inaktivierung der Pilzstämme aus der Notwendigkeit von Neuisolierungen hervor, die vorgenommen verden mußten.
Für die Cattleyagruppe und Rh. repens behielten die Isolierungen eine zureichende Aktivität in folgenden Perioden: Am Ende der Periode mußten Neuisolierungen vorgenommen verden: 1908/09; 1910/11; 1912/13; folgt eine durch meinem Kriegsdienst gegebene Pause: 1924/25; 1926/28; 1929/35. Von den 1929 isolierten Pilzen blieb zum mindesten einer aus einer Importpflanze von Cattleya Mossiae bis 1935 aktiv."

(Burgeff, 1936., p. 236.)

How he knew that all of these "Neuisolierungen" were indeed Rhizoctonia repens strains?

"Beide Autoren haben mit Cattleyen gearbeitet, die zur biologischen gruppe des Rhizoctonia repens Bernard - Pilzes gehören."
The two authors referred to are Knudson and Quednow.

(Burgeff, 1936., p. 384.)

"R. repens Bernard -- Myc. white, recumbent, creeping, no aerial hyphae. Sporodochia small, white, confluent in a continuous layer over the surface of agar media. Spores nearly spherical, in staphylococcoid cluster of short branched chains, 13-19 µ by 10-14 µ.Figure 8. Mycelium entirely submerged in liquid cultures.

Isolated from: Brassia gireoudiana, San Isidro, Costa Rica; Calopogon pulchellus, moist prairie, Waukesha County, Wisconsin; Goodyera pubescens, pine covered talus slope, Sauk County, Wisconsin; Goodyera repens var. ophioides, hemlock woods, Sheboygan County, Wisconsin; Liparis Loeselii, sphagnum bog, Ozauke County, Wisconsin; Pogonia ophioglossoides, open sphagnum bog, Ozauke County, Wisconsin; Spiranthes cernua, habitat unknown, Hanover, New Hampshire."

(Curtis 1939., p. 395)

   "Rhizoctonia repens Bernard, Ann. Sci. nat. Botan., Sér. 9:26-31.1909     On PDA the colony is colorless, with thin, white, recumbent, creeping mycelium and no aerial hyphae. In older colonies the mycelium grows mostly within the substrate, and the colony surface becomes smooth.
    The vegetative hyphae are septate, hyaline, branching at right angles, with the first septum a few microns beyond the point of origin. The main branch hyphae are 2,5-4,5 µ wide, with short side branches up to 6 µ wide.
    The white sporodochia are variable on different substrates. On PDA they are confluent in a continuous layer over the surface of media; on CMA they are submerged, flat, round, 80-125 µ in diameter; on the walls of test tubes with seedlings, they are granular and up to 150 µ in diameter.
    The chlamydospores (Fig. 3) are hyaline, globose, 12,5-17,5 X 11,5-16 µ in diameter. Chlamydospore chains are short, branched, and borne frequently on lateral sporophore-like hyphae. The chains occur singly snd in sporodochia.
    Sclerotia have not been observed.
    Isolated in culture from mycorrhizal rootlets of Pinus banksiana, Pineland, Manitoba, 1956 (No. 2583), and from damped-off seedlings of P. sylvestris, Indian Head, Saskatchewan 1956 (No. 2331).
Other specimen examined: R. repens Bernard obtained from the Centraalbureau voor Schimmelcultures.

    R. repens was originally isolated and described by Bernard as an orchid symbiont. Later it was reported from various orchid species of Germany and Java (3, 4), and the United States (11). Hildebrand and Koch (21) reported a Rhizoctonia similar to R. repens associated with root rot of strawberry and tobacco in Canada. It is here recorded definitely for the first time in Canada and on new hosts."

From Saksena and Vaartaja (1961.)

a) Bibliographic data refer only to the pages on which Bernard described his isolates,
b) The detail mentioning that Bernard isolated this fungus also from the fern Ophioglossum is missing,
c) Bernard's remark that "Filaments moniliformes ... jamais anastomosés." is also missing in spite of the fact that this is a diagnostic feature of Bernards's isolate(s),
d) the concept of Saksena and Vaartaja was that measurements are of taxonomic value, however, size differences existing between the data given by Burgeff and their own isolate are glossed over,
e) at the time of publication there were at least four R. repens strains deposited at the CBS, however, the oldest one was deposited by Vermeulen only in 1932, i. e. there was no surviving culture of Bernard's original R. repens isolate(s),
f) Marianne Stahl's work on the thalloid liverworth Aneura pinguis yielding a similar if not identical microfungus in 1949 is not even mentioned.

See also M. Stahl:

"Nicht ganz sicher erscheint die Zugehörigkeit von Rhizoctonia aneurae pinguis E (Hochschwab) zur Rhizoctonia repens-Gruppe, da die Monilien wesentlich grösser sind als die dort beschreibenen. Sie werden auch auf höher konzentrierten Stärkeböden ausgebildet."

(Planta vol. 37, p. 141. 1949.)