Rhizoctonia

Rhizoctonia is largely known as the root-cause of a wide range of plant diseases. Most of the literature you'll come across focusses on Rhizoctonia as a plant pathogen of foodcrops and trees. Fortunately, this means that a great deal of research has been done on identification and growth requirements for these species. A large portion of this information can be ported into fungal culture, but please keep in mind that as a hobbyist you're a candidate source of contamination for other plants. Some species have the ability to fuse hyphae cells (anastomosis, the primary means of genetic recombination in Rhizoctonia 1)). This is probablt the reason for the multi-nucleic cells (and similar host ranges) in some species.

Rhizoctonia as part of the "Mycelia Sterilia" group: they don't produce asexual spores but multiply via the thin hyphae. The Teleomorph stage is rare in nature (which has led to maintaining their Mycelia Sterilia classification) but have been observed under controlled conditions. Many species have been classified in the basidiomycete genera Thanatephorus, Waitea, and Ceratobasidium. Because Rhizoctonia species often do not produce spores, these fungi are identified by characteristics of their hyphae. Rhizoctonia hyphae produce branches at right and acute angles to the main hypha, the branch hypha is slightly constricted at the branch origin, and there is often a septum near the branch origin2). Rhizoctonia species also produce specialized hyphae composed of compact cells called monilioid cells 3). The monilioid cells fuse together to produce hard structures called sclerotia 4), which are resistant to environmental extremes, allowing the fungus to survive adverse conditions.

Rhizoctonia sp.

Isolated from crown and root rot of Vanda sp. 5)

Germination of Spiranthes sinensis var. amoena in vitro 6) - paper concludes that in situ and in vitro specificity is different.

Rhizoctonia borealis J.T. Curtis, Am. J. Bot. 26: 393 (1939)

Synonym of Thanatephorus cucumeris (A.B. Frank) Donk 1956

requires acid soils under conifers. Associated with European orchids Spiranthes gracilis and Goodyera repens. 7)

Isolated from roots of Goodyera sp. 8)

Isolated from roots of Spiranthes sp. 9)

Rhizoctonia carotae

Rhizoctonia cerealis

Teleomorph: Ceratobasidium cornigerum.

Plant pathogen in barley (Hordeum vulgare), rye (Secale cereale) and wheat (Triticum spp.), a rust known as "sharp eyespot". Hypha cells have 2 nuclei 10)

Rhizoctonia lanuginosa

Isolated from roots of Calopogon sp. 11)

Isolated from roots of Goodyera sp. 12)

Rhizoctonia leguminicola

Plant pathogen on red clover (Trifolium pratense), Black Patch Disease. 13)

Rhizoctonia monilioides

Isolated from roots of unknown terrestrial Orchid sp. 14)

Isolated from roots of unknown Habenaria sp. 15)

Isolated from roots of unknown Pogonia sp. 16)

Isolated from roots of Spiranthes sp. 17)

Rhizoctonia neotia

Isolated from roots of Aplectrum sp. 18)

Rhizoctonia oryzae

Hypha cells have more than 2 nuclei. 19) Produces colonies on PDA that are white, buff, or salmon colored. Sclerotia of R. oryzae are salmon colored, 1 mm (0.04 in.) to 3 mm (0.12 in.) in diameter, and form on the agar surface or submerged in the agar. Grows optimally in pure culture at 32ºC, and contains only one anastomosis group (R. oryzae - WAG-O). Less sensitive to dicarboximide fungicides than R. solani. 20)

Rhizoctonia repens

Isolated from roots of unknown terrestrial Orchid sp. 21)

Isolated from roots of Calopogon sp. 22)

Isolated from roots of Goodyera sp. 23)

Isolated from roots of unknown Habenaria sp. 24)

Isolated from roots of unknown Pogonia sp. 25)

Isolated from roots of Spiranthes sp. 26)

Germination of Spiranthes sinensis var. amoena using in situ seed baiting 27)

Rhizoctonia robusta

Isolated from roots of Cypripedium sp. 28)

Isolated from roots of unknown Habenaria sp. 29)

Rhizoctonia rubi Plant pathogen

Rhizoctonia sclerotica

Isolated from roots of Cypripedium sp. 30)

Isolated from roots of unknown Habenaria sp. 31)

Isolated from roots of Spiranthes sp. 32)

Rhizoctonia solani

Teleomorph: Thanatephorus cucumeris, 11 anastomosis groups (AG 1 & 2 associated with turfgrass disease)
A plant pathogen with worldwide distribution, one of the fungi knwon to cause damping off. Does not produce spores.

Isolated from Pterostylis acuminata, teleomorph formation failed 33)

Isolated (AG 6) from Pterostylis acuminata 34)

Isolated from root and stem rot of unknown Orchid sp. 35)

Isolated from root and stem rot of xBrassolaeliocattleya sp. 36)

Isolated from root and stem rot of Cattleya sp. 37)

Isolated from root and stem rot of Cymbidium sp. 38)

Isolated from root and stem rot of Dendrobium sp. 39)

Isolated from root and stem rot of Epidendrum sp. 40)

Isolated from root and stem rot of xLaeliocattleya sp. 41)

Isolated from root and stem rot of Oncidium sp. 42)

Isolated from root and stem rot of Phalaenopsis sp. 43)

Isolated from root and stem rot of Vanda sp. 44)

R. solanii hypha cells have more than 2 nuclei. 45)
Culture: Potato Dextrose Agar between 18°C and 28°C 46), colonies have a color ranging from broken white to black. Irregularly shaped sclerotia (> 1mm width) on the surface of cultures after 4-6 weeks.

Rhizoctonia sphacelati

Isolated from roots of unknown Habenaria sp. 47)

Rhizoctonia stahlii

Isolated from roots of unknown Habenaria sp. 48)

Isolated from roots of Spiranthes sp. 49)

Rhizoctonia subtilis

Isolated from roots of Cypripedium sp. 50)

Isolated from roots of unknown Habenaria sp. 51)

Rhizoctonia subtilis var. nigra

Isolated from roots of Spiranthes sp. 52)

Rhizoctonia zeae

Hypha cells have more than 2 nuclei. 53) Produce colonies on PDA that are white, buff, or salmon colored. Sclerotia are initially white, but eventually turn to orange then red or dark brown, are uniformly spherical, and form submerged in the agar medium. Grows optimally in pure culture at 32ºC, and contains only one anastomosis group (R. zeae - WAG-Z). Less sensitive to dicarboximide & to benzimidazole fungicides than R. solani. 54)