Pseudokeissleriella tetradii L.X. Mi & D.M. Hu, 2025

Mi, Li-Xue, Song, Hai-Yan, Eungwanichayapant, Prapassorn D. & Hu, Dian-Ming, 2025, Integrative taxonomy reveals Pseudokeissleriella tetradii sp. nov. (Lentitheciaceae, Pleosporales) associated with Tetradium ruticarpum in Anhui Province, China, Phytotaxa 710 (2), pp. 165-183 : 170-177

Pseudokeissleriella tetradii L.X. Mi & D.M. Hu sp. nov. Figure 2

Index Fungorum Number: IF903759; Facesoffungi Number: FOF17679.

Etymology: The name reflects the host genus, Tetradium , from where the fungus was isolated.

Holotype: HFJAU10463

Endophytic fungus in the healthy stem of Tetradium ruticarpum ( Rutaceae ). Sexual morph: Undetermined. Asexual morph: Coelomycetous. Mycelium densely branched, 1–4 μm wide, hyaline, subhyaline to pale brown, septate, smooth-walled. Conidiomata 150–700 μm diam, pycnidial, solitary to aggregated, globose to subglobose,

tef 1 -α

black, glabrous or with few hyphal outgrowths, superficial on the agar or semi-immersed. Ostiole inconspicuous. Conidiomatal wall pseudoparenchymatous, composed several layers of brown cells of textura angularis. Conidiophores reduced to conidiogenous cells. Conidiogenous cells 2.8–4 × 1–1.5 μm (x = 3.5 × 1.3 μm; n = 50), holoblastic, hyaline, smooth-walled, ampulliform to doliiform, proliferating percurrently at apex, hyaline, smooth-walled. Conidia 2.8–4 × 1–1.5 μm (x = 3.5 × 1.3 μm; n = 50), hyaline, cylindrical to subcylindrical, biguttulate, rounded at both ends, straight, aseptate, thick- and smooth-walled.

Culture characteristics: Colonies growing on PDA, reaching a diameter of 40 mm after 16 days at 25 °C, nearly circular, surface slightly rough, woolly or cottony, olive-grey to pale grey from centre to margin, reverse light yellow at the centre, grading to dark olive-grey, becoming pale grey at the margin. No visible pigmentation.

Material examined: CHINA, Anhui Province, Xuancheng City, Xuanzhou District , on the healthy stems of Tetradium ruticarpum , 30.88° N 118.78° E, altitude 46m, 22 May 2022, Lixue Mi, dry culture (HFJAU10463, holotype), ex-type JAUCC 6570 ; ibid, 30.90° N, 118.73° E, altitude 17.76m, 8 September 2023, Lixue Mi, dry culture HFJAU10464, living culture JAUCC 6578 ; ibid, dry culture HFJAU10465, living culture JAUCC 6586 .

Notes: Pseudokeissleriella tetradii (JAUCC 6570) was morphologically identified as the asexual morph (anamorph). Direct morphological comparison is unfeasible since Ps. tetradii is an asexual morph, while Ps. bambusicola (CGMCC 3.20950) was described based on its sexual morph. However, this species aligns with the anamorphic characteristics defined for Lentitheciaceae , demonstrating pycnidial conidiomata with globose morphology, enteroblastic conidiogenous cells, and unicellular cylindrical conidia that are hyaline with smooth walls ( Hyde et al. 2013). Moreover, the multi-locus phylogenetic analysis ( Figure 1 ) strongly supports the close relationship between Ps. tetradii and Ps. bambusicola , with high statistical support (ML bootstrap = 98.8% in SH-aLRT, UFBoot = 100%, Bayesian posterior probability = 1.0). The pairwise genetic distances between Ps. tetradii and Ps. bambusicola for different loci are as follows: ITS (2.75%), LSU (0.44%), SSU (0.00%), and tef 1-α (1.28%). These values fall below the intergeneric divergence thresholds typically observed within Lentitheciaceae . Furthermore, the ITS divergence (2.75%) exceeds the intraspecific variation commonly observed in closely related fungal species ( Jeewon & Hyde 2016), supporting Ps. tetradii as a distinct species rather than an asexual morph of Ps. bambusicola . Thus, given the above morphological and molecular evidence, we introduce Ps. tetradii as a new species, representing its first documented asexual morph.

Figures

FIGURE 1. Maximum likelihood phylogenetic tree of Lentitheciaceae and representatives in Massarineae based on combined SSU, ITS, LSU, and tef1-α sequence data, with Shimodaira–Hasegawa-like approximate likelihood ratio test (SH-aLRT) (left), ultrafast bootstrap (UFB) (middle), and Bayesian posterior probabilities (BPP) values (right) near the corresponding node. Thickened branches indicate branch support with SH-aLRT/UFB/BPP = 100/100/1. Only one of SH-aLRT> 80 or UFB> 95 for ML and BYPP> 0.90 for BI are indicated along branches (SH-aLRT/UFB/BPP). Newly generated sequences are highlighted in red. Strains in bold with a superscript “T” indicate ex-type strains.

FIGURE 2. Pseudokeissleriella tetradii (HFJAU10463, holotype). a Host. b, c Colonies on PDA from surface and reverse. d, e Conidiomata on PDA. f A section through conidioma. g A section of peridium. h Mycelium. i–k Conidiogenous cells and developing conidia. l–o Conidia. Scale bars: f, g = 300 μm, h–o = 10 μm.