Paraphoma populi S.S. Xiang & C.L. Yang, in Yang, Li, Xiang, Xu, Zeng, Sun, Liu, Maharachchikumbura, Lv, Wang, Ji-Zuo, A-Niu & Liu, Mycosphere 16(1): 1915 (2025)

Index Fungorum number: IF 901631, MycoBank number: MB 901631, Facesoffungi number: FoF16126

Etymology – Refers to the host genus Populus.

Holotype – SICAU 23-0149

Associated with leaf spots on leaves of Populus × beijingensis W. Y. Hsu. Sexual morph: Not observed. Asexual morph: Coelomycetous. Conidiomata 109–143 × 65–128 μm (x̄ = 120 × 87 μm, n = 10), pycnidial, long ellipsoid, semisubmerged, aggregated, dark brown. Conidiomatal wall composed of 2–3 layers of chartreuse textura globulosa, with brown cells in the outer layer and hyaline cells in the inner layer. Conidiophores reduced to conidiogenous cells. Conidiogenous cells 2.5–5 × 3–6 μm (x̄ = 3.6 × 4.6 μm, n = 30), densely aggregated, smooth, ellipse, subulate, mostly straight, phialidic, simple, cylindrical, hyaline. Conidia 4–6 × 2–3 μm (x̄ = 4.8 × 2.6 μm, n = 50), solitary, subglobose or ovoid, smooth-walled, aseptate, obtuse at both ends.

Culture characteristics – Germinated conidia on PDA within 12 h and germ tubes produced from both ends. Colonies on PDA attaining 21–24 mm after 12 days, circular, surface with thick aerial mycelium, initially appearing white and light yellow, becoming flavovirens from the center with age, in reverse light yellow to dark brown with smooth margin, pigmentation in the center.

Material examined – China, Sichuan Province, Chengdu City, Wenjiang District, Gongping Street, Sichuan Agricultural University. 103°51′27.55″E 30°42′19.5″N, 533 m, isol. from leaves of Populus × beijingensis, 3 Nov. 2020, C.L. Yang, YCL202011001 (SICAU 23-0149, holotype), extype culture (SICAUCC 23-0097). ibid., YCL202011001-2 (SICAU 23-0157), living culture SICAUCC 23-0132.

GenBank numbers – SICAUCC 23-0097 = LSU: PP719620, SSU: PP734051, tef1-α: PQ005619, ITS: PP769689. SICAUCC 23-0132 = LSU: PP719625, SSU: PP734053, tef1-α: PQ005622, ITS: PP769693

Notes – In the phylogenetic analyses using combined ITS, LSU, SSU, and tef1-α sequence data, Paraphoma populi clusters with P. convolvuli, P. dioscoreae, P. garibaldi, P. melnikiae, and P. salicis (98% MLBS / 1.00 BYPP) (Fig. 33). In comparative sequence analyses, the ITS and LSU sequences of N. populi show notable differences when compared with other species. For P. convolvuli (MF-9.222), the ITS similarity is 88.3% (424/480, 4 gaps), and LSU similarity is 99.4% (840/845, 0 gap). Compared with P. dioscoreae (CBS 135100, holotype), the ITS similarity is 86.9% (449/517, 6 gaps) and LSU is 99.5% (831/835, 0 gap). For P. salicis (CPC 38651, holotype), the ITS similarity is 90.2% (525/582, 4 gaps) and LSU is 99.6% (833/836, 0 gap). In comparison with P. melnikiae (MF-9.95, holotype), ITS similarity is 88.4% (428/484, 8 gaps) and LSU is 99.3% (839/845, 0 gap). For P. garibaldi (CBS 148459, holotype), the ITS similarity is 97.7% (414/472, 5 gaps). Morphologically, P. populi can be readily distinguished from P. convolvuli and P. melnikiae based on the septation and size of the conidia (P. populi: 0-septate, 4–6 × 2–3 μm vs. P. convolvuli: 2–3-septate, 15–18 μm; P. melnikiae: 0–2-septate, 9–22 × 2–4 μm) (Gomzhina et al. 2020). Paraphoma populi differs from P. dioscoreae by having subglobose to ovoid conidia, as opposed to the cylindrical conidia of P. dioscoreae, and by the absence of droplets (0 droplet vs. 2 droplets in P. dioscoreae) (Quaedvlieg et al. 2013). Compared with P. garibaldi, the conidiomata of P. populi are smaller (109–140 μm vs. 200–300 μm) and lack setae, and the conidia have no droplets (Guarnaccia et al. 2022). Compared with P. salicis, P. populi has smaller conidiomata (109–140 μm vs. 180–200 μm) and produces thicker aerial mycelia on PDA (Crous et al. 2021). The morphological characteristics and molecular phylogenetic analyses support the recognition of a new species.

Figure 1 – Paraphoma populi (holotype, SICAU 23-0149). a Symptoms on the leaf. b, c Appearance of conidiomata. d Cross-section of conidioma. e Conidiomatal wall. f Conidiogenous cells with developing conidia. g Conidia. h Germinating conidium. i Front and reverse view of colonies on PDA. Scale bars: b, c = 200 μm, d, e = 10 μm, f–h = 5 μm.