Claviceps africana Frederickson, Mantle & De Milliano

Synonym

Sphacelia sorghi McRae

Description

Sclerotia formed in the fertile florets of spikelets and replacing the ovaries, oval-spherical, 4-6 mm long x 2-3 mm wide; the pyramidal apical sphacelial portion protruding beyond the floral parts; the hard basal portion (the true sclerotium) appearing flecked red by fragments of adherent sphacelial tissue overlaying a red-brown cortex.

Conidia of three types

  • microconidia formed on narrow, flask-shaped terminal conidiogenous cells on the sphacelium and later immersed in honeydew, spherical, 2-3 μm in diameter, hyaline.
  • macroconidia formed on narrow, flask-shaped terminal conidiogenous cells on the sphacelium and later immersed in honeydew, oblong-oval and slightly constricted at the middle, 9-17 x 5-8 μm, hyaline, aseptate.

  • secondary conidiadeveloped above the honeydew surface singly at the tips of sterigmata from germinated macroconidia, broadly pyriform, 11-19 x 5-8 μm, hyaline, aseptate; en masse forming a white coating in the honeydew surface.

Ascostromata 1-9 per sclerotium, arising at one or two points on the sclerotium surface; each consisting of a sub-globose capitulum 0.5-1.3 mm, dark purple, papillate at maturity and enveloping the stipe insertion, borne by a stipe 8-15 mm long x 0.3-0.6 mm wide, glabrous, initially translucent whitish later purple, especially in the distal portion.

Perithecia immersed in the capitulum, ovate-pyriform, 123-226 μm long x 86-135 μm wide.

Asci in perithecia cylindrical, up to 140 μm long, 3-4 μm wide.

Ascospores filiform, up to 45 μm long, 0.8-1.2 μm wide, multi-septate, hyaline.

Hosts
   
Host family: Poaceae
   
Host species: Pennisetum glaucum
Sorghum almum
Sorghum bicolor
Sorghum bicolor x sudanense
Sorghum halepense
Sorghum plumosum

Distribution

NT, QLD, SA, WA, known from NSW

Comments

Frederickson et al. (1991) separated C. africana from Claviceps sorghi McRae (which up until that time was considered to be the only Claviceps species on Sorghum bicolor) on the basis of differences in the colour and texture of the stromata, dimensions of asci and ascospores, and mode of development of sclerotia. The ascostromata of this species have been observed only in vitro. Since its discovery in 1996, Claviceps africana has spread throughout Australia, and is found wherever grain and forage sorghum and its weed hosts grow (Ryley et al., 2002). The airborne secondary conidia of C. africana are believed to be its main mode of dispersal. In Australia, C. africana has considerable impacts in some years on the production of commercial grain and hybrid seed through increased production costs, and on the livestock industries due to the toxicity of contaminated grain, mainly by the alkaloid dihydroergosine.

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Claviceps africana on Unknown host.
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Claviceps africana on Unknown host.
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Claviceps africana on Sorghum sp.
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Claviceps africana on Sorghum sp.
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Claviceps africana on Sorghum sp. - BRIP 23278.
Scale bar = 20 µm.
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Claviceps africana on Sorghum sp. - BRIP 23278.
Scale bar = 10 µm.
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Claviceps africana on Sorghum sp. - BRIP 23278.
Scale bar = 10 µm.
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Claviceps africana secondary conidia.
Scale bar = 10 µm.
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Claviceps africana secondary conidia.
Scale bar = 10 µm.
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Claviceps africana secondary conidia.
Scale bar = 10 µm.