Conidiosporomyces ayresii (Berk.) Vánky

Synonyms

Tilletia ayresii Berk.
Tilletia heterospora (Henn.) Zundel
Ustilago evansii Henn.
Ustilago heterospora Henn.

Description

Sori in some ovaries of an inflorescence, inflated, ovoid or cylindrical, 2.5–5.0 (–10) mm long, 1.5–3.0 mm wide, composed of an apically open sack-like leathery membrane and a grey to pale olive-brown semi-powdery central mass of spores, sterile cells and balls of conidia. Columella absent. Sorus membrane thickest (10–20 µm) at the base of the sorus, gradually thinning distally, dark olivaceous or reddish brown at the base, pale greyish brown at its open distal part, composed of an external layer of host tissue and an internal layer of sporogenous fungal tissue, restricted to the proximal half of the sorus. Sporogenous tissue composed of closely packed septate branched hyphae c. 1.5 µm diam. Intercellular fungal hyphae present in the proximal half of the sorus membrane. Haustoria and clamp connections absent.

Spores globose, subglobose to broadly ellipsoidal, 13–17 × 12–16 µm, yellowish brown to dark brown, finely to coarsely verrucose; warts c. 1–2 µm high, subacute or flattened, in SEM rounded, often with a short narrow tip, sometimes 2 or more fusing (dimensions varying between spores and also on the same spore).

Spore germination resulting in aerial holobasidia to 40 µm long and c. 5 µm wide, but basidia may remain included in the spore; distal part of basidium dividing into 2–8 short branches. Basidiospores 10–24, produced on short apical tubercles on the branches, long-cylindrical, slightly curved, 30–36 × 2 µm, hyaline, germinating at both ends without conjugation, giving rise to branched septate hyphae on which both blastic conidia and ballistospores are produced. Ballistospores germinating by blastic conidia, hyphae or Y-shaped conidia.

Sterile cells globose, subglobose or ellipsoidal, subhyaline to pale yellow, 14.5–21.5 × 13.5–20.0 µm, sparsely, moderately or densely verruculose, relatively thin-walled (1.5–2.0 µm), often with a large vacuole, collapsed in dried specimens. Differences between spores and sterile cells not always sharp; the relatively small globose thin-walled apparently smooth hyaline cells between the spores may be either immature spores or young sterile cells. Balls of conidia globose, 25–55 µm diam., composed of many loosely connected conidia; spores, sterile cells and balls of conidia produced by the sporogenous hyphae on the inner side of the sorus membrane and pushed toward the centre of the sorus. Conidial balls presumably produced by repetition, as in culture. Conidia thin-walled (c. 0.5 µm), smooth, hyaline, varying greatly in shape, usually Y-shaped, but also triangular, T-, club-, boomerang-shaped, or somewhat branched, with 2 rounded and widened branches and 1 gradually narrowing to pointed branch, 10–16 (–20) µm long, usually 2.5–3.0 µm wide. Germination of conidia resulting in hyphae on which both blastic conidia and ballistospores are formed, like those produced from the germination of basidiospores. Rod-shaped conidia producing Y-shaped conidia or hyphae bearing ballistospores, Y-shaped and rod-shaped conidia. Balls of conidia formed in culture of basidiospores by repetition of Y-shaped conidia. In cultures of basidiospores on MYP, after 3 weeks, inflated globose or ellipsoidal hyaline thin-walled cells were seen (possibly spores and/or sterile cell initials). Ballistospores, Y- and rod-shaped conidia mononucleate in culture. Hyphal cells long and probably mononucleate.

Host-parasite interaction by intercellular hyphae; interaction apparatus lacking.

Septal pore of Tilletia-type, a dolipore traversed by 2 membraneous plates; pore caps lacking.

Hosts
   
Host family: Poaceae
   
Host species: Megathyrsus maximus (Jacq.) B.K.Simon & S.W.L.Jacobs
Megathyrsus maximus var. pubiglumis (K.Schum.) B.K.Simon & S.W.L.Jacobs
Panicum antidotale Retz.

Distribution

States & Territories: QLD

Comments

Conidiosporomyces ayresii was first found in Australia in 2005 in south-eastern Queensland and in 2006 in northern Queensland. Its apparent absence from Australia until recently is unusual as Conidiosporomyces ayresii occurs in most tropical and subtropical regions, especially on its principal host Megathyrsus maximus.