Diaporthe eucommiigena S. Y. Wang, Yong Wang bis & Y. Li

Li, Xinyue, Xu, Xiulan, Xiang, Shasha, Liu, Feng, Wang, Feihu, Jiang, Xuejing, Liu, Yinggao & Yang, Chunlin, 2025, Morpho-phylogenetic evidence reveals two new species and two new host records of Diaporthe (Diaporthales, Diaporthaceae) from Phellodendron chinense in Sichuan, China, MycoKeys 123, pp. 205-233 : 205-233

Diaporthe eucommiigena S. Y. Wang, Yong Wang bis & Y. Li , Journal of Fungi 8: 1301 (2022)

Fig. 3

Description.

Saprobic on decaying branch of Phellodendron chinense . Sexual morph: Not observed. Asexual morph: Coelomycetous. Conidiomata 164–246 × 121–151 μm (x ̄ = 208 × 132 μm, n = 10), initially immersed, becoming erumpent at maturity, discoid to conical, brown, unilocular or multilocular, mostly single-loculate, solitary or aggregated, with a distinct ostiole. Conidiomatal wall 9–24 μm wide (x ̄ = 14.6 μm, n = 20), composed of multiple layers of thick-walled, pale to medium brown cells of textura angularis or textura globulosa, with pigmentation gradually fading towards the interior. Conidiophores reduced to conidiogenous cells. Conidiogenous cells 5–13 × 1.4–3.8 μm (x ̄ = 10.1 × 2.2 μm, n = 20), hyaline, cylindrical or pyriform, apex slightly tapering, terminal. Alpha-conidia 7.2–8.9 × 1.9–3.3 μm (x ̄ = 7.9 × 2.7 μm, n = 30), hyaline, aseptate, smooth-walled, ellipsoid to fusiform, usually containing two guttules. Beta-conidia and Gamma-conidia not observed.

Culture characteristics.

Alpha-conidia germinated in sterile water within 24 h at 25 ° C. Colonies on PDA attaining 50–55 mm diam. in 7 d at 25 ° C. Colony irregular, density moderate to high, margin undulate, surface densely cottony to floccose and strongly rugose, white to creamy-white, consistency soft, elevation low-convex centrally, plane to slightly raised towards the periphery, edge well-defined. Zonation indistinct. Pycnidia scattered, more frequent near the periphery. Reverse olivaceous to dark olivaceous-brown with uneven pigmentation forming an interlaced pattern. Sporulation observed after approximately 20 d in culture, producing alpha-conidia.

Material examined.

• China, Sichuan Province, Leshan City, Jinkouhe County, Jixing Village , 29°16'58.10"N, 103°13'7.42"E, 1599 m elev., from branches of Phellodendron chinense , 1 May 2024, X. Y. Li, LXY 202405014 A ( SICAU 25-0159 ), culture ( SICAUCC 25-0131 ) ; ibid., LXY 202405014 B ( SICAU 25-0160 ), culture ( SICAUCC 25-0132 ) .

Notes.

Diaporthe eucommiigena was originally described by Wang et al. (2022) from dead wood of Eucommia ulmoides in China. In a recent taxonomic revision, Dissanayake et al. (2024) treated D. eucommiigena as a synonym of D. passiflorae , based on overlapping micromorphological features of alpha conidia. However, our study revealed that these two taxa occupy distinct lineages in the multigene phylogenetic tree. Moreover, clear morphological and molecular differences support their recognition as separate species. Morphologically, beta conidia of D. eucommiigena are longer (27–37 × 1–2 μm vs. 16–18 × 1.5 μm), whereas its gamma conidia are smaller (7.5–10 × 1.5–2.5 μm vs. 10–12 × 2–2.5 μm) ( Crous et al. 2012; Wang et al. 2022). Pairwise nucleotide comparisons further distinguish the two species. Diaporthe passiflorae ( CBS 132527 , holotype) and D. eucommiigena ( GUCC 420.9 , holotype) differ by 1.88 % (11 / 585, 0 gap) in ITS, 6.65 % (23 / 346, 8 gaps) in tef 1 - α and 3.04 % (13 / 427, 1 gap) in tub 2. Taken together, we propose the retention of D. eucommiigena as a distinct species, separate from D. passiflorae .

Two newly-obtained isolates, SICAUCC 25-0131 and SICAUCC 25-0132 , clustered with Diaporthe eucommiigena with a strong support (100 % MLBS / 1.00 BYPP; Fig. 1 ). Morphologically, these isolates are consistent with D. eucommiigena , producing cylindrical, slightly tapering conidiogenous cells and hyaline, ellipsoid to fusiform, guttulate alpha conidia (7.2–8.9 × 1.9–3.3 μm vs. 5.5–8 × 1.5–3 μm). Nucleotide comparisons between SICAUCC 25-0131 and the ex-type strain GUCC 420.9 revealed minimal variation, with 0.61 % (3 / 488, 0 gap) in ITS, 1.11 % (5 / 450, 1 gap) in tub 2 and 2.82 % (8 / 284, 6 gaps) in tef 1 - α (Table 3 ). Although the tef 1 - α region exhibits comparatively higher divergence, the isolates are morphologically concordant with the ex-type and differ only marginally in ITS and tub 2 regions. Consistent with current guidance, which requires that new species be diagnosable by a unique combination of characters with at least two to three phenotypic differences ( Jeewon and Hyde 2016) and recommends that slight variation in short DNA fragments should not on its own warrant taxonomic novelty, but be evaluated within an integrative framework that weighs morphology together with multilocus evidence ( Jeewon and Hyde 2016; Aime et al. 2021; Chethana et al. 2021), we consider the single-locus signal from tef 1 - α insufficient to justify a new species and, therefore, retain SICAUCC 25-0131 and SICAUCC 25-0132 within D. eucommiigena , which is the first report on Phellodendron chinense in Sichuan, China.

Figures

Figure 1. Maximum Likelihood phylogenetic tree, based on concatenated sequences of the ITS, tef 1 - α, tub 2, cal and his 3 gene regions from Diaporthe species. Bootstrap support values ≥ 60 % (left) and Bayesian posterior probabilities ≥ 0.90 (right) are shown at the nodes. Isolates from the present study are indicated in bold. Ex-type or ex-epitype strains are marked with “ T ”.

Figure 3. Diaporthe eucommiigena (SICAU 25-0159). a. Habitat of Phellodendron chinense; b, c. Conidiomata on host surface; d, e. Section through conidiomata; f. Ostiole; g. Conidiomatal wall; h – j. Conidiogenous cells bearing conidia; k. Alpha-conidia; l. Germinating alpha-conidium; m. Colony on PDA (left: above, right: reverse). Scale bars: 400 μm (c), 50 μm (d – f), 20 μm (g), 10 μm (h – l).