Pseudoplagiostoma jasmini

Pseudoplagiostoma jasmini Gomdola, K.D. Hyde & Jayaward., sp. nov.                      

Index Fungorum number: IF 900131, Facesoffungi number: FoF 14104

Etymology: The specific epithet refers to the host genus, Jasminum, from which the species was isolated.

Holotype: MFLU 23-0068

Associated with leaf spots of Jasminum grandiflorum. Leaf spots irregular, pale to medium brown, surrounded by a dark brown to black margin. Sexual morph: Not observed. Asexual morph: Coelomycetous. Conidiomata (145–)150–230(–240) μm diam., (135–)140–200 μm high (= 184 × 171 μm, n = 20), pycnidial, semi-immersed, solitary, scattered, uniloculate, globose to subglobose, pale brown, surrounded with black margin. Conidiomata wall (19–)22–42(–46) μm thick (= 28 μm, n = 15), consisting of 3–4 layers of thick-walled pseudoparenchymatous cells of textura angularis, outer layers dark brown to black, inner layers pale brown to hyaline. Conidiophores indistinct, often reduced to conidiogenous cells. Conidiogenous cells phialidic, (6.8–)7.7–13.7(–15.6) × 1.6–2.4(–3.0) μm (= 10.7 × 2.1 μm, n = 10), hyaline, cylindrical or clavate, guttulate, smooth-walled, proliferating enteroblastically. Conidia (11.8–)14–22 × (5.2–)6.5–11 μm (= 18.5 × 9.5 μm, n = 50), hyaline, guttulate, 0–2-septate, smooth, wall (0.5–)0.6–1.3 μm thick (= 0.8 μm, n  =  50), cylindrical to truncate or ellipsoidal, elongated, reniform, pyriform or obovoid, apex broadly obtuse, tapering towards a slightly curved base, often with a prominent protruding hilum. Appressorium 9.6 × 7.2 μm long, single-celled, sub-ellipsoidal to obovoid or subglobose or irregular-shaped, hyaline.

Culture characteristics: Colonies on MEA reaching approximately 20 mm diam. after 14 days of incubation at 25 °C, immature with white mycelium, elevation flat or raised, becoming aerial dense and olivaceous brown, filamentous with an undulate margin when aged.

Material examined: Thailand, Chiang Mai Province, Doi Inthanon National Park, Kew Mae Pan nature trail, on fallen leaves of Jasminum grandiflorum (Oleaceae), 20 October 2021, D. Gomdola, DG-PSEU (MFLU 23-0068, holotype), ex-type living culture MFLUCC 23-0044.

GenBank accession numbers: ITS = OQ786078, 28S = OQ786079, β-tub = OQ850148 and tef-1α = OQ850145.

Notes: Pseudoplagiostoma jasmini groups with other species of Pseudoplagiostoma and forms a sister clade with P. dipterocarpicola (MFLUCC 21-0142 and MFLUCC 21-0114) with 35% ML-IQ, 32% MP, and 0.95 PP support (Fig 2). The features are congruent with the morphological species concept of Pseudoplagiostoma (Cheewangkoon et al. 2010).

Pseudoplagiostoma jasmini varies substantially in conidial shape (Fig 5). Conidia of P. jasmini are longer than those of P. dipterocarpicola (MFLUCC 21-0142) (Table 1). The conidial length-to-width ratio of P. jasmini is 2.0, whereas that of P. dipterocarpicola is 2.7.

Excluding gaps in our aligned untrimmed dataset, in pairwise nucleotide comparisons of P. jasmini and P. dipterocarpicola (MFLUCC 21-0142), the following differences were observed: 5.76% across ITS (543 nucleotide base pairs, bp), 1.86% across 28S (818 bp), 21.1% across β-tub (448 bp), and 43.7% across tef-1α (164 bp). The inter-species genetic distances (%) grouped according to the PTP result are provided (Table 2).

Based on the guidelines of Chethana et al. (2021), Jayawardena et al. (2021), and Maharachchikumbura et al. (2021) for introducing new species, we describe P. jasmini as a new species. Despite its support values (35% ML-IQ, 32% MP, and 0.95 PP), we establish P. jasmini as a new taxon, considering the formation of one or two septa in the conidia, a feature lacking in all other Pseudoplagiostoma species; all Pseudoplagiostoma spp. have aseptate conidia. Besides morphology and multigene phylogenetic analyses, we included GCPSR and PTP analyses as further evidence to support the distinct species status of Pseudoplagiostoma jasmini.

Fig 1. Pseudoplagiostoma jasmini (MFLUCC 23-0044, ex-holotype) (a) Leaf of Jasminum grandiflorum with spots. (b) Appearance of conidiomata on leaves. (c) Close up of conidioma on substrate. (d) Section through a conidioma. (e–h) Conidiophores, conidiogenous cells, and developing conidia. (i–t) Conidia with guttules, septa and protruding hilum. (u–v) Top (left) and reverse (right) of colonies on MEA after 7 and 14 days of incubation, respectively. (w) Appressorium. Scale bars: b = 1 mm, c = 200 μm, d = 100 μm, e–t = 10 μm, w = 20 μm

Table 1. Morphological comparison of Pseudoplagiostoma jasmini with P. dipterocarpicola.

L/W: Length-to-width ratio.

Table 2. Genetic distance (%) between Pseudoplagiostoma species (grouped according to PTP results) in the concatenated ITS, 28S, β-tub, and tef-1α genetic markers.

N/A: not applicable.

Fig 2. Maximum likelihood phylogram based on the combined ITS, 28S, β-tub, Rpb2, and tef-1α matrices of Pseudoplagiostoma. Bootstrap support values (ML-IQ ≥ 30%) and maximum parsimony (MP ≥ 30%), and Bayesian posterior probabilities (PP ≥ 0.80) are given above the branches or at the nodes as ML-IQ/MP/PP. Hyphen (-) indicates bootstrap support values below 30% for ML-IQ and MP, and posterior probabilities below 0.80. Apoharknessia eucalypti (CBS 142518), A. eucalyptorum (CBS 142519), and Apoharknessia insueta (CBS 111377 and CBS 114575) are the outgroup taxa. Ex-type and reference strains are in bold, and the new taxon is in bold red.

Genealogical Concordance Phylogenetic Species Recognition Analysis (GCPSR)

The LogDet transformation and splits decomposition options were selected while configuring the PHI test. The analysis yielded a threshold over 0.05 (Фw = 0.7314) for the new species, Pseudoplagiostoma jasmini, indicating no significant recombination (Fig 3).

Fig 3. Split graph derived from the PHI analysis, generated for Pseudoplagiostoma. The novel species is in bold red.

Poisson Tree Processes

The result generated from the PTP analysis (Fig 4) is congruent with the maximum likelihood phylogram that delimits Pseudoplagiostoma jasmini as a new species (Figure 1). Genetic distances of Pseudoplagiostoma jasmini compared with its phylogenetically closely related taxa are summarized in the “note” section under Pseudoplagiostoma in the “Taxonomy” section.

Fig 4. Results generated from the PTP analysis of Pseudoplagiostoma. The analysis was based on the ML-IQ topologies of the concatenated ITS, 28S, β-tub, and tef-1α matrices. Groups of species are denoted by colored branches, with blue-colored branches indicating that they are different species, and red-colored branches representing different strains of the same species. Numbers near the nodes are posterior probabilities. The new taxon is given in bold red.