Warcup & P.H.B. Talbot (1962)
Rhizoctonia zeae Voorhees (1938) (anamorph)
Waitea circinata is a species of fungus in the family Corticiaceae. Basidiocarps (fruit bodies) are thin, effused, and web-like, but the fungus is more frequently encountered in its similar but sterile anamorphic state, sometimes called Rhizoctonia zeae. Waitea circinata is best known as a plant pathogen, causing commercially significant damage to cereal crops and turf grass.
Waitea circinata was originally described from Australia in 1962, where it was found growing on the undersides of clods of earth in a wheat field. The new genus Waitea, named after the Waite Agricultural Research Institute in Adelaide, was created to accommodate the species. Because of its morphological similarity to species of Rhizoctonia and Thanatephorus, Waitea circinata was presumed to belong within the Ceratobasidiaceae, but cladistic analysis of DNA sequences has shown that it actually belongs in the Corticiaceae and is close to species of Laetisaria (which are also grass pathogens).
The anamorphic species Rhizoctonia zeae, originally described as the causal agent of ear rot of maize, is a synonym of Waitea circinata. Rhizoctonia oryzae has also been considered a synonym, but the name is not validly published and is of doubtful application (it has also been considered a synonym of Rhizoctonia solani). The name Rhizoctonia circinata has been used for the anamorph of Waitea circinata, but is not validly published and appears to be a portmanteau error.
Molecular research has shown that Waitea circinata is divided into four genetically distinct clades and that representatives of these clades cause visibly different diseases. They have been considered varieties of the species ("var. circinata", "var oryzae", "var. zeae", and one unnamed), but the named varieties have not been formally described or validly published.
Basidiocarps are effused, thin, web-like, smooth, white to pale ochre. Hyphae are multinucleate, colourless, often irregular, 2.5-11 μm wide, without clamp connections. Basidia are often constricted about the middle, with four short sterigmata. Basidiospores are smooth, oblong to cylindrical, 8-12 by 3.5-5 μm, colourless to pale ochre. Sclerotia are pinkish orange to brown, 0.5–3 mm wide.
Habitat and distribution
The species appears to be a soil saprotroph, principally associated with grasses, possibly always as a pathogen. Though first described from Australia, it has a cosmopolitan distribution but is commonest in warmer climates, producing optimal growth at around 25-35 °C.
Waitea circinata is the causal agent of a range of diseases of cereal crops and amenity turf grasses. These include ear rot, root rot, and stalk rot of maize, sheath spot of rice, and various leaf & sheath spots of turf grasses.
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