Tilletia walkeri Castlebury & Carris

Description

Sori in ovaries enclosed by the pericarp, inconspicuous, infecting only 1 or 2 per spike, the ovaries usually only partially destroyed; spore mass dark brown, with no obvious odour.

Spores globose to subglobose, 24–36 (–40) × 23.5–36.0 (–39.0) µm, yellowish to dark reddish brown, ornamented with conical to truncate warts 3–5 µm high; in surface view appearing coarsely and incompletely cerebriform to coralloid, with a hyaline to yellowish brown sheath extending to the tips of warts.

Sterile cells globose, subglobose, ellipsoidal or lacrymiform, 13–26 (–32) µm long, hyaline to yellowish brown; wall 1.5–4.0 (–5.0) µm thick, laminated; intermediate forms (immature spores) frequent, smaller, pale, finely ornamented, usually thick-walled.

Spore germination resulting in a short aseptate multinucleate basidium on which basidiospores are produced in a terminal whorl. Basidiospores (36–) 60–150 (–230), filiform, curved, 38–75 × 1.3–1.8 µm, hyaline, initially mononucleate, rapidly undergoing nuclear division and forming inconspicuous septa between daughter nuclei (typically 1 septum per basidiospore); fusion between basidiospores lacking. Secondary sporidia developing following the germination of basidiospores, of two types: allantoid with a truncate base, 10.6–17.6 × 1.8–3.1 µm, hyaline; filiform and curved, 26.0–57.2 × 1.8–2.6 µm, hyaline. Allantoid sporidia forcibly discharged, produced asymmetrically from sporogenous cells formed on hyphae, basidiospores or secondary sporidia; sporogenous cells subulate, 4.5–7.0 µm high, 1.3–2.2 µm wide at base, 0.9 µm wide at apex, hyaline.

Hosts
   
Host family: Poaceae
   
Host species: Lolium perenne L.

Distribution

States & Territories: NSW

Comments

It is remarkable that all Australian specimens of T. walkeri were found in commercial seedlots of Lolium perenne (perennial ryegrass) harvested in Kangaroo Valley, New South Wales (from several locations listed above) in the 1960s and early 1970s. Tilletia walkeri has never been recorded in the field in Australia, although it has established on Lolium multiflorum (annual ryegrass) in the U.S.A. grown from seed exported from Australia (Castlebury & Carris, 1999). Tilletia walkeri has comparatively large spores and thereby bears some resemblance to T. indica which has not been recorded from Australia (Pascoe et al., 2005b).