Polyschema radicicola F. Q. Sun, Kumla, Phookamsak & Suwannar. sp. nov.

Fig. 4

Etymology.

The species epithet “ radicicola ” refers to the root from which the species was isolated.

Type.

China • Yunnan Province: Honghe Prefecture, Honghe County, isolated from healthy root of baobab tree, 23°25'21"N, 102°14'19"E, elevation 503.7 m, 25 June 2024, F. Q. Sun, BR 16-1, dried herbarium culture KUN - HKAS 150834 (Holotype, preserved in a metabolically inactive state), ex-type living culture KUNCC 25-20159.

Description.

Dark brown, filamentous, septate endophyte (DSE) isolated from healthy root of baobab tree (Adansonia digitata). Mycelium 1.7–4.0 µm wide, superficial, composed of branched, narrow, septate, hyaline to light brown hyphae, flexuous hyphae, smooth-walled when young, straight or curved, coarsely roughened when mature, minutely echinulate or verruculose. Conidiophores 7.2–10.3 × 3.4–6.1 µm (x ̄ = 8.8 × 4.8 μm, n = 50), micronematous, solitary, erect, hyaline to pale brown, unbranched, clavate, or short cylindrical, or reduced to conidiogenous cells. Conidiogenous cells 4.4–7.2 × 4.3–7.3 µm (x ̄ = 5.8 × 5.9 μm, n = 30), monotretic, solitary, terminal or lateral, globose, clavate or short cylindrical, hyaline, smooth-walled. Conidia solitary, mostly pleurogenous, at times acrogenous, usually borne along the axis of conidiogenous cells, but sometimes obliquely oriented, cylindrical, slightly constricted at septa, pale brown, end cells paler, dark brown to black at the septa, verrucose to echinulate surfaced, (2–5) - septate, 20.4–40.9 × 7.5–13.1 µm (x ̄ = 31.0 × 10.5 μm, n = 50).

Culture characteristics.

Colony grows slowly on PDA, reaching 15 mm in seven days at room temperature (25–30 ° C) under dark conditions, colonies irregular, felted, slightly heaped and folded, pale brown when immature, becoming completely brown when mature, producing orange pigment.

Additional materials examined.

China • Yunnan Province: Honghe Prefecture, Honghe County, isolated from healthy root of baobab tree, 23°25'21"N, 102°14'19"E, elevation 503.7 m, 25 June 2024, F. Q. Sun, BR 16-5, ex-paratype living culture KUNCC 25-20160.

Notes.

Polyschema radicicola is basal to a subclade containing P. adansoniae-digitatae (KUNCC 25-20156 and KUNCC 25-20157), P. congolense (CBS 542.73), and P. hongheense (KUNCC 25-20158). These species form a subclade and have a close relationship with P. endophytica (COAD 3972) and P. terricola (CBS 301.65). Based on nucleotide comparisons, P. radicicola KUNCC 25-20159 (holotype) differs from P. congolense CBS 542.73 (holotype) in the ITS sequence by 34 / 548 bp (6.2 %, including 14 gaps), in the LSU sequence by 14 / 846 bp (1.7 %, including one gap), and in the rpb 2 sequence by 82 / 768 bp (10.7 %, including three gaps). Polyschema radicicola KUNCC 25-20159 differs from P. hongheense KUNCC 25-20158 by 5.8 % nucleotides in ITS (30 / 518 bp, including nine gaps), 1.4 % nucleotides in LSU (12 / 844 bp, including one gap), 2.3 % nucleotides in SSU (31 / 1336 bp, including nine gaps), and 8.9 % nucleotides in rpb 2 (94 / 1060 bp, including four gaps). Polyschema radicicola KUNCC 25-20159 differs from P. endophytica COAD 3972 (holotype) by 9.4 % nucleotides in ITS (52 / 556 bp, including 28 gaps) and 2.0 % nucleotides in LSU (17 / 849 bp, including four gaps), and differs from P. terricola CBS 301.65 (holotype) by 11.4 % nucleotides in ITS (57 / 501 bp, including 33 gaps), 2.3 % nucleotides in LSU (20 / 852 bp, including seven gaps), and 10.0 % nucleotides in rpb 2 (77 / 769 bp, including three gaps).

Morphologically, Polyschema radicicola is distinguishable by its colony producing orange pigment (Table 2). Furthermore, P. radicicola exhibits mycelial hyphae that are occasionally narrow, flexuous, and smooth-walled, yet remain capable of generating conidiogenous cells and conidia. Conidia of P. radicicola differ from those of P. terricola (Ellis 1976) by being longer and narrower (20.4–40.9 × 7.5–13.1 µm vs. 15–35 × 13–18 μm), cylindrical, distinctly echinulate at the surface, and transversely 2–5 - septate, lacking vertical septa, whereas P. terricola has transversely 0–3 - septate conidia with sometimes one longitudinal or oblique septum (Ellis 1976). Polyschema congolense (Reisinger and Kiffer 1974) can be distinguished from P. radicicola by having smaller (16–26 × 8–11 μm) and 2–3 - septate conidia, commonly with two septa. Polyschema hongheense differs by having shorter (12.8–36.6 × 7.4–13.6 µm), paler brown, 1–4 - septate conidia, commonly with 1–2 septa and occasionally formed terminally. Polyschema endophytica (Crous et al. 2025) differs by having aseptate, globose, subglobose to ellipsoidal, smooth-walled conidia.