Sporisorium australasiaticum Vánky & R.G. Shivas

Description

Sori in the spikelets destroying the inner floral organs, ±hidden by the outermost floral envelopes, globose to ovoid, 1–2 mm long, 1.0–1.5 mm wide, at first covered by a thick brown peridium that ruptures irregularly exposing the dark brown powdery mass of spores and sterile cells surrounding a simple central columella sometimes with short apical branches. Rarely, the sori occupying 1 or several racemes or entire inflorescence branches, then cylindrical and up to 30 mm long.

Spores when mature solitary, subglobose, ovoid to broadly ellipsoidal, 8–11 × 7.5–9.5 µm, yellowish brown; wall uniformly c. 0.5 µm thick, with a paler rounded area 1.0–1.5 µm diam., probably a germ pore; spore surface in LM finely verruculose; spore profile smooth to very finely serrulate; in SEM finely echinulate, between the spines densely and finely verruculose.

Sterile cells in small groups; individual cells usually irregular with flattened contact sides, 6–16 µm long, hyaline; wall uniformly c. 0.5 µm thick, smooth.

Hosts
   
Host family: Poaceae
   
Host species: Sarga leiocladum (Hack.) Spangler

Distribution

States & Territories: QLD

Comments

Sporisorium australasiaticum can be distinguished from three similar species on Sarga and Sorghum, viz. S. cruentum (J.G.Kühn) Vánky, S. sorghi and S. ryleyi (Vánky & Shivas, 2001) by its sorus and spore morphology. The peridium of S. australasiaticum is thick and persistent, and the spores are verruculose and comparatively large with germ pores (not always visible under light microscopy). Only S. cruentum has not been reported from Australia.