Austrophoma euphorbiae N.Q. Pham, Marinc. & M.J. Wingf., in Marincowitz, Pham, Wingfield, Roets & Wingfield, Fungal Systematics and Evolution 12: 66 (2023)

Index Fungorum number: IF 849173, MycoBank number: MB 849173, Facesoffungi number: FoF 15898

Etymology – The name refers to the host genus Euphorbia.

Diagnosis – Similar to other phoma-like species but differs in having hyaline and rectangular-shaped (in side view) conidia.

Typus – South Africa, Northern Cape Province, Namakwa District Municipality, Nieuwoudtville Falls, from dying Euphorbia mauritanica, Aug. 2020, M.J. Wingfield (holotype PRU(M) 4548, culture ex-type CMW-IA 49, CMW 56351).

GenBank Accession numbers: OR198840 (ITS); OR198846 (LSU); OR211854 (TUB2); OR211851 (RPB2).

Description – Sexual morph: unknown. Asexual morph: on 2 % MEA. Conidiomata pycnidial, immersed to superficial in medium, globose to ellipsoidal, ovoid; base pale brown when young becoming dark brown to black with age, 122–396 × 91–490 (214 ± 64.1 × 197 ± 100.5) µm; protruding ostioles, or necks absent or present, single or multiple when present, 72–533 µm long. Conidiomatal walls pseudoparenchymatous, textura angularis, in two tiers, 16–34 (25 ± 4.3) µm thick, outer tier composed of 3–5 layers of thick-walled, moderately compressed, brown cells, inner tier composed of thin-walled, compressed, hyaline cells. Conidiophores on entire layer of inner cavity, reduced to conidiogenous cells. Conidiogenous cells holoblastic, cylindrical. Conidia hyaline, cylindrical, with round apex and flat base, mostly straight, occasionally curved, aseptate, rarely 1-septate, 8–14 × 3–4 (10.4 ± 1.37 × 3.2 ± 0.32) µm, oozing out in milky slimy mass.

Culture characteristics – Colonies on MEA showing optimum growth at 25 °C (5.3 mm/d), followed by 20 °C (5.2 mm/d), 15 °C (4 mm/d), 10 °C (2.5 mm/d), 30 °C (0.5 mm/d) and 35 °C (0.4 mm/d). Colonies on MEA at 25 °C in the dark for 28 d fuscous black (3’’’’’k) above and reverse, sparse aerial hyphae, with even edge. Colonies at lower temperatures colour becoming paler.

Host – Euphorbia mauritanica.

Distribution – South Africa (Northern Cape Province).

Notes – Austrophoma had a close affinity to phoma-like genera in the Didymellaceae in multi-gene analyses. The most closely related genera were AscochytaLeptosphaerulinaMicrosphaeropsisNeomicrosphaeropsisNothomicrosphaeropsisParamicrosphaeropsis and Phomatodes. In addition to its differences in molecular characteristics, Austrophoma can be distinguished from Ascochyta by producing pycnidia (on MEA) with papilla or distinguishing necks. Ascochyta produces ostiolate or poroid pycnidia, without a distinct form of neck (). Austrophoma is different from Microsphaeropsis and its derivative genera containing the name ‘microsphaeropsis’ by having hyaline conidia: MicrosphaeropsisParamicrosphaeropsis, (), Nothomicrosphaeropsis () and Neomicrosphaeropsis () produce pigmented conidia. Austrophoma and Phomatodes () are morphologically similar to each other in having hyaline conidia in allantoid to cylindrical conidia, but combined sequence data separate them into distinct lineages. No sexual morph was found with Austrophoma, whereas Leptosphaerulina and Neomicrosphaeropsis have sexual morphs producing muriform ascospores.

Figure 1 – Micrographs of Austrophoma euphorbiae sp. nov. (ex-type: CMW-IA 49, CMW 56351). A. Colony with abundant pycnidia on 2 % MEA after 60 d in the dark at room temperature. B, C. Young and mature pycnidia with ostiolar protruding, single or multiple necks. D, E. Vertical sections through pycnidia. F. Pycnidial wall. G. Conidiogenous cells. H. Conidia. I. Colony morphology on 2 % MEA incubated in the dark for 28 d at different temperatures. Scale bars: A = 1 mm; B, C = 100 µm; D–F = 50 µm; G, H = 10 µm.