Verruconis pakchongensis Chuaseehar., Nuankaew, Somrith. & Boonyuen, sp. nov.

Index Fungorum number: IF 900202; Mycobank number: MB 900202; Facesoffungi number: FoF 15103; Fig. 1

Etymology – The specific epithet “pakchongensis” refers to the Pak Chong District, Nakhon Ratchasima Province, Thailand where the holotype was collected.

Holotype – BBH 49597

Saprobic or opportunistic pathogens on other fungi. Sexual morph: Not observed. Asexual morph: Hyphomycetous. Colonies forming on conidiophores of unidentified fungus, caespitose, effuse, loose to dense, hairy, brown. Mycelium 1.5–2.8 μm diam, superficial, composed of branched, septate, smooth-walled, pale brown hyphae, occasionally forming anastomosis hyphae. Conidiophores 21.5–34.2×2.1–2.7 μm (x̄=28.4×2.5 μm, n=20), arising laterally from hyphae, mononematous, solitary to loosely
aggregated, simple or rarely branched, subcylindrical, straight or slightly flexuous, 2–4-septate, smooth-walled, pale brown. Conidiogenous cells up to 13.2×1.8–2.7 μm (x̄=10×2.4 μm, n=20), holoblastic, polyblastic, integrated, terminal, with sympodial extensions, subcylindrical, denticulate, pale brown, with 1–3 cylindrical denticles at the apical region, 0.6–2.2×0.7–1.3 μm. Conidia 6.8–8.9×4–4.7 μm (x̄=8×4.3 μm, n=10), acropleurogenous, solitary, broadly ellipsoidal with rounded ends, 1-septate, deeply constricted at the septum, rough-walled, greyish brown. Conidial secession rhezolytic.

Culture characteristics – Colonies after 14 days at 25 °C: On MEA reaching 22–26 mm diam., cottony, brown, round, margins mostly entire, soluble pigment absent, exudates absent, reverse brown. On PDA reaching 21–26 mm diam., velvety, greyish brown, round, margins mostly entire, soluble pigment yellowish brown, exudates absent, reverse brown. Vegetative hyphae on PDA medium 1.5–4 μm diam., composed of branched, septate, smooth or rough-walled, pale brown. Conidiophores 5.2–35×1.8–2.8 μm (x̄=13×2.3 μm, n=20), arising laterally from vegetative hyphae, mononematous, solitary, simple or occasionally branched, subcylindrical, straight or flexuous, 0–3-septate, smooth-walled, pale brown, or reduced to a single conidiogenous cell that arise from assimilative hyphae. Conidiogenous cells up to 12.5×1–3.7 μm (x̄=8.3×2.3 μm, n=15), holoblastic, mostly monoblastic, integrated, terminal, with sympodial extensions, or lateral, subcylindrical or ampulliform, denticulate, pale brown, with 1–3 cylindrical denticles at the apical region, 1–1.2×0.5–0.7 μm. Conidia 6.2–9×3.6–6.1 μm (x̄=7.8×4.6 μm, n=30), acrogenous or pleurogenous, solitary, broadly ellipsoidal, broadly obovoid to subglobose, rounded ends, 0–1-septate, often constricted at the septum, rough-walled, greyish brown, sometimes with a gelatinous brown sheath. Conidial secession rhezolytic. Chlamydospores 10.7–14 μm, terminal or intercalary, solitary, subglobose, aseptate, smooth-walled, brown.

Material examined – Thailand, Nakhon Ratchasima Province, Pak Chong District, Khao Yai National Park, Pha Diao Dai Nature Trail, isolated from conidiophores of unidentified fungus, on decaying wood of an unidentified plant in a small pond, 27 July 2011, C. Chuaseeharonnachai, isolate FF00304 (BBH 49597, holotype), ex-type TBRC-BCC 51642.

GenBank numbers – TBRC-BCC 51642: act=OQ116769, ITS=OQ121928, LSU OQ121946, rpb2=OQ116751, SSU: OQ121937, tef1-α=OQ116760, tub2=OQ116768.

Notes – Our isolate (TBRC-BCC 51642) belongs to Verruconis and is phylogenetically close to the clade that includes V. cylindricalis and V. guizhouensis, with 90% ML bootstrap and 1.00 BYPP value (Fig. 2). They are morphologically similar in that they possess integrated and terminal or sympodial conidiogenous cells on solitary conidiophores which produce 1-septate and rough-walled conidia (Shao et al. 2022; Wei et al. 2022a). However, V. pakchongensis is distinguished from these two species mainly by the presence of unicellular conidia and, sometimes, brown gelatinous sheaths on its conidia. Morphologically, V. pakchongensis has more variable in conidial shape with broadly ellipsoidal and broadly obovoid to subglobose (Fig. 1), while the conidia of V. cylindricalis and V. guizhouensis are regular in broadly ellipsoidal and ellipsoidal (Shao et al. 2022; Wei et al. 2022a), respectively. Furthermore, V. pakchongensis differs from V. cylindricalis and V. guizhouensis in producing terminal or intercalary, subglobose, aseptate, and smooth-walled chlamydospores. Chlamydospores of V. guizhouensis are intercalary, ellipsoidal, 1-septate, and verrucose (Shao et al. 2022), whereas those of V. cylindricalis are intercalary, cylindrical or clavate, 2-septate, and verruculose (Wei et al. 2022a). In addition, reverse colonies of V. cylindricalis produce blood-colored diffusible pigments on both MEA and PDA media (Wei et al. 2022a), whereas V. pakchongensis produces yellowish brown on PDA and V. guizhouensis produces brown diffusible pigments on MEA (Shao et al. 2022), based on observations after 14 days of incubation at 25–26 °C. Both morphology and DNA sequence data support the distinction of V. pakchongensis as the novel taxon in this study.

Figure 1 – Verruconis pakchongensis (BBH 49597, holotype). a, b Colonies with conidia on conidiophore of unidentified fungus. c–f Upper and reverse views of culture on PDA (the top) and MEA (the bottom), after 14 days at 25 °C. g–k, m Conidiophores, conidiogenous cells and conidia on PDA, arrow indicates a gelatinous brown sheath. l Chlamydospore. Scale bars: a=20 μm, b=5 μm, g–m=10 μm

Figure 2 – Phylogram generated from maximum likelihood analysis (RAxML) of Verruconis and its allied genus in the Sympoventuriaceae based on the combined SSU, LSU and ITS sequence data. Fifty taxa are included in the combined analyses, which comprise 3,275 characters with gaps. Pseudosigmoidea excentrica (CBS 469.95) and Sympoventuria capensis (CBS 120136) were chosen as the outgroup. The best scoring RAxML tree with a final likelihood value of − 26,937.672831 is presented. The matrix had 1282 distinct alignment patterns, with 24.62% of undetermined characters or gaps. The proportion of invariable sites was 0.488513. Estimated base frequencies were as follows: A=0.240109, C=0.231110, G=0.302179, T=0.226602; substitution rates: AC=0.814969, AG=1.615578, AT=0.983656, CG=0.991532, CT=3.660408, GT=1.00000; gamma distribution shape parameter α=0.411956. Bootstrap support values for ML equal to or greater than 70% and BYPP equal to or greater than 0.95 are given near the nodes. T=ex-type strain. The newly generated sequences are indicated in blue bold