Tilletia triraphidis T. Denchev & Denchev, 2018

Denchev, Teodor T., Zon, A. P. M. Van Der & Denchev, Cvetomir M., 2018, Tilletia triraphidis (Tilletiaceae), a new smut fungus on Triraphis purpurea (Poaceae) from Namibia, Phytotaxa 375 (2), pp. 182-186 : 183

Tilletia triraphidis T. Denchev & Denchev , sp. nov. ( Figs 1–12 )

Index Fungorum number: IF 554293

Type: —On Triraphis purpurea Hack. ( Poaceae ). NAMIBIA. Erongo Region: Dâures Constituency, near Uis Mine, 5 April 1950, leg. H. G. Schweickerdt 2254 ( SOMF 29 921, holotype).

Diagnosis: —Differs from all other Tilletia species by specialization on Triraphis .

Etymology: —The epithet refers to the host genus.

Sori in swollen ovaries (only some spikelets of the inflorescence affected; in the affected spikelets the ovaries of all fertile florets are infected), broadly fusiform or ellipsoid, 2–3 mm long, with a short, acute tip, bearing a rudimentary style and stigmas, visible between the spreading floral bracts, covered by a thick, purplish brown to yellow-brown pericarp that later ruptures longitudinally, exposing a powdery, blackish brown mass of spores and sterile cells. Sterile cells very often larger than the spores, variable in shape, sizes, colour, and wall thickness, usually irregular, sometimes subglobose, ellipsoidal, broadly ellipsoidal or pyriform, (16.5–)18–48(–55) × (14–)16.5–38(–41) (32.2 ± 6.7 × 25.8 ± 5.6) μm (n = 400), hyaline to light yellow-brown; cell wall irregularly thickened, (1.6–)2.0–6.5(–7.5) μm thick, distinctly laminate, mainly in large-sized and thick-walled sterile cells, or indistinctly laminate or one-layered in sterile cells with smaller sizes and thinner cell wall; sterile cells sometimes with a papilla or narrow appendage. In SEM smooth, punctate, minutely verruculose or moderately verruculose (warts often confluent forming small groups or short rows), sometimes wrinkled. Spores subglobose, broadly ellipsoidal, globose, slightly irregular or ovoid, sometimes pyriform, (24–)25–35(–40) × (21.5–)23–31(–33) (29.8 ± 2.5 × 26.1 ± 2.2) μm (n = 400), dark or very dark reddish brown, completely reticulate, sometimes incompletely reticulate; spore wall (4.0–)4.3–5.5(–5.8) μm thick, a faint, 0.8–1.2 μm thick inner layer may be observed in some lighter-coloured spores and in the immature spores; meshes 3–5(–6) per spore diameter, polyhedral or irregular, (1.6–)2.2–8.5(–12) μm long; muri (10–)11–15(–16) on equatorial circumference, in optical median view subacute or acute, 0.7–2.3(–2.8) μm high; spores sometimes with a hyaline papilla, extending up to 4.5(–6) μm beyond the muri, or with a narrow, hyaline appendage. In SEM interspaces rugulose or smooth, occasionally with a protuberance.

Known host and distribution: —On Poaceae : Triraphis purpurea , Africa ( Namibia), known only from the type collection ( Fig. 13 ).

Comments: —The spore wall is hard to observe in the very dark reddish brown spores.

Triraphis purpurea is endemic to southern Africa. It is distributed from the southernmost provinces of Angola (Namibe and Cunene) through Namibia and Botswana to North West province and Northern Cape province of South Africa ( Klaassen & Craven 2003, Costa et al. 2004, Fish & Victor 2005, Müller 2007).

Only three smut fungi, all of them members of Ustilago , have been previously recorded on plants in the tribe Triraphideae : U. neyraudiae Mundk. on Neyraudia arundinacea (L.) Henrard and N. reynaudiana (Kunth) Hitchc. from Asia ( China, India, and Thailand; Guo 2000, Shivas et al. 2007, Vánky 2011), U. latzii Vánky on Triraphis mollis R. Br. from Australia ( Vánky & Shivas 2008), and U. triraphidis Vánky on Triraphis schinzii Hack. from Africa ( Zambia; Vánky 2011, Vánky et al. 2011). Tilletia triraphidis can easily be differentiated from these species by having sterile cells and reticulate spores.

Figures

FIGURE 13. Map of Namibia with type locality of Tilletia triraphidis indicated by a black circle (generated with d-maps, https://d-maps. com/carte.php?num_car=4824&lang=en).

FIGURES 1–12. Tilletia triraphidis sp. nov. (from holotype). 1. Habit (most florets in the unaffected spikelets have fallen off). 2. Sterile cells and a spore. 3. Sterile cell with a papilla (arrow). 4. Sterile cell with an appendage (arrow). 5–6. Spores in LM (in median and surface view, respectively). 7. Immature spore (left) (arrow shows the inner layer of the spore wall). 8. Spore with a hyaline papilla (arrow). 9. Spore with a hyaline appendage (arrow). 10–12. Spores and sterile cells in SEM. Scale bars: 1 = 1 cm, 2–11 = 10 μm, 12 = 5 μm.