Sporisorium ryleyi Vánky & R.G. Shivas

Description

Sori in the spikelets destroying the inner floral organs, rarely also the basal part of the glumes, ovoid to elongate-ellipsoidal, 1.5–4.0 mm long, 1.0–1.5 mm wide, ±hidden by the glumes, at first covered by a thick brown peridium that ruptures irregularly exposing the dark brown powdery mass of spores and sterile cells surrounding a thick simple central columella c. length of the sorus.

Spores solitary when mature, globose, subglobose, ellipsoidal, rarely ovoid or elongate, 4.5–6.5 (–7) × 4.0–5.5 µm, olivaceous brown; wall uniformly c. 0.5 µm thick, finely verruculose; spore profile smooth.

Sterile cells usually in small groups; individual cells subglobose to usually irregular with flattened contact sides, 5–12 µm long, hyaline; wall uniformly 0.5–0.8 µm thick, smooth.

Spore germination of Ustilago-type, with 4-celled basidia producing lateral and terminal basidiospores after 1 day on water agar.

Hosts
   
Host family: Poaceae
   
Host species: Sarga leiocladum (Hack.) Spangler
Sarga plumosum (R.Br.) Spangler
Sarga timorense (Kunth) Spangler

Distribution

States & Territories: NT, QLD, WA

Comments

There has been confusion in the literature regarding the identification of smut fungi on the native Australian species of Sorghum. McAlpine (1910) made the new combination Cintractia columellifera (Tul.) McAlpine based on Ustilago carbo (DC.) Tul. var. columellifera Tul. and listed a specimen from Rockhampton on Andropogon australis. The host was subsequently determined to be Sorghum leiocladum (= Sarga leiocladum) by C.E.Hubbard (Langdon, 1962). Langdon (1962) noted that confusion had resulted when later workers tried to identify various smuts on andropogonoid grasses as C. columellifera. From a study of some smut fungi on Sorghum, Langdon (1962) considered that the specimen from Rockhampton, as well as some others on the native species, Sorghum leiocladum and Sorghum plumosum, were best referred to Sphacelotheca sorghi (Ehrenb. ex Link) G.P.Clinton (= Sporisorium sorghi Ehrenb. ex Link).

More recently, Vánky & Shivas (2001) have shown that there are seven species of smut fungi on Sorghum (including Sarga) in Australia. Three of these, Sporisorium australasiaticum, S. ryleyi and S. wynaadense, occur on Sarga leiocladum. Sporisorium ryleyi differs from the other smut fungi on Sarga and Sorghum by the smaller spores size. It is similar to S. sorghi, which has larger spores that measure 5.5–8.0 (–8.5) × 5.5–7.0 µm. However, S. sorghi, the cause of covered kernel smut of cultivated sorghum, is not known to occur on any of the Australian species of Sarga.

Sporisorium ryleyi is most likely to be confused with S. australasiaticum, which occurs on native species of Sorghum and Sarga. However, the spores of S. australasiaticum are significantly larger (7.5–11.0 µm long). Accordingly, specimens of the small-spored smut on native Sarga in Australia, including the specimen from Rockhampton studied by McAlpine (1910), are referable to S. ryleyi.