Ustilago scitaminea Syd.

Synonyms

Sphacelotheca miscanthi W.Y. Yen
Sporisorium miscanthi (W.Y. Yen) L. Guo
Sporisorium scitamineum (Syd.) M. Piepenbr.
Ustilago amadelpha Syd., P. Syd. & E.J. Butler
Ustilago scitaminea var. sacchari-barberi Mundk.
Ustilago scitaminea var. sacchari-officinarum Mundk.

Description

Sori in floral stems that are transformed into long flagelliform often curved bodies; basal part of the sori concealed by leaf sheaths, distal part free and tapering, at first covered by a silvery peridium of host tissue which flakes away exposing the blackish brown dusty mass of spores mixed with irregular groups of sterile cells.

Spores globose, subglobose to subovoid, 6.5–8.0 (–10) × 5.5–7.5 µm, reddish brown; wall uniformly 0.5–0.8 µm thick, from ±smooth, finely and sparsely punctate-verruculose to sparsely or moderately densely echinulate.

Sterile cells larger than the spores (8–23 µm diam.), yellow or pale yellowish brown, smooth.

Spore germination resulting in 4-celled basidia (often of 3 + 1 pattern; the fourth basidial cell remaining within the spore) on which ovoid to long-ellipsoidal lateral and terminal basidiospores are produced. Basidiospores budding or fusing in pairs, giving rise to dikaryotic hyphae. Under natural conditions, on sugarcane (and on certain media), basidial cells conjugate and produce septate dikaryotic infection hyphae.

Hosts
   
Host family: Poaceae
   
Host species: Saccharum officinarum L.

Distribution

States & Territories: QLD, WA

Comments

Ustilago scitaminea causes a devastating and widespread disease of cultivated sugarcane in most tropical and subtropical countries, although it is absent from Papua New Guinea. It was detected for the first time in Australia in the Ord River Irrigation Area (ORIA) in the semi-arid tropics of Western Australia in July 1998 (Riley et al., 1999). The ORIA is about 2,500 km from Java, Indonesia where high levels of sugarcane smut are known to occur. Quarantine regulations were subsequently enacted to prevent the movement of the smut from the ORIA to the sugarcane production areas along the eastern seaboard of Australia. However, in June 2006 sugarcane smut was detected at Childers in south-eastern Queensland. Subsequently it was detected at Mackay in central Queensland and at Ingham in northern Queensland. It is now considered to be established and widespread.

Ustilago scitaminea has morphological characteristics that resemble Sporisorium rather than Ustilago, viz. the presence of groups of sterile cells between the spores, the whip-like remnants of the floral axis as a columella and a peridium that covers the young sori. However, partly because U. scitaminea is the name known by plant pathologists as the causal organism for sugarcane smut, and partly because the generic limits between Ustilago and Sporisorium are unresolved, we retain this name. A proposal by Vánky & Shivas (2005) to conserve U. scitaminea against an earlier name, U. amadelpha Syd., P.Syd. & E.J.Butler, was accepted at the International Botanical Congress in Vienna in 2006.