Scolecobasidium laurentii M. Suthar, S.K. Singh & P.N. Singh, 2025

Suthar, Malika, Singh, Sanjay K. & Singh, Paras N., 2025, Scolecobasidium laurentii (Sympoventuriaceae, Venturiales) a new species described based on morphology and molecular phylogeny from Western Ghats, India, Phytotaxa 711 (2), pp. 170-182 : 175-179

Scolecobasidium laurentii M. Suthar, S.K. Singh & P.N. Singh , sp. nov. ( Figs. 1–3 )

MycoBank:—857711

Holotype:— AMH 10780

Etymology:—The specific epithet laurentii is dedicated to Professor Laurent Dufossé, a distinguished Professor from Reunion Island University, France, to commemorate his contributions to the study of microbial pigments.

Host/Distribution:—from the detritus-rich soil of Tamhini Ghats, Maharashtra, India.

Description: — Asexual morph. Hyphae branched, septate, septa thickened and darkened (band-like), pigmented, smooth-walled, hyaline to light olivaceous, anastomosis present. Indeterminate synnemata, light olivaceous to olivaceous, compact to loosely arranged. Chlamydospores absent, stroma, setae and hyphopodia absent. Conidiophores macronemmatous, mononematous, erect, developing from superficial lateral hyphae, variable in dimension, 0–6 septate, unbranched or rarely branched, rarely rudimentary, light olivaceous to olivaceous, smooth-walled, wall thickened and darkened, 8.5–30 (rarely up to 120.5 µm) × 0.85–2.05 µm, straight to flexuous, cylindrical to ampulliform, width increasing towards apex, terminal part of conidiophore rarely bulged. Conidiogenous cells mono- to polyblastic, integrated, terminal to lateral, sympodial, cylindrical to denticulate, denticles long, narrow, cylindrical, threadlike, smooth-walled, hyaline, variable in dimension, 1.03–5.67 × 0.46–0.87 µm. Conidia solitary, dry, acrogenous to acropleurogenous, ellipsoidal, fusiform, base narrowly truncate, thickened, apex obtuse, sub-hyaline to light olivaceous, smooth to minutely verruculose, constricted near septa, 0–1 septate, septa thickened and darkened, rarely catenate, bipolar germination, clavate, rarely guttulate, 3.35–8.62 × 2.13–3.58 µm. Conidial appendages aseptate, smooth-walled, hyaline, cylindrical, tip sub-obtuse and rarely branched ( Figure 1 ).

Culture characteristics:— Colonies on PDA after 10 days—18 × 18 mm, slow growing, forming cushion— floccose to velvety, front—3D2 (olive grey), margins smooth, reverse—8F3 (greyish brown), after 10 days forming erect synnemata, indeterminate. Colonies on MEA after 10 days—23 × 23 mm, moderately growing, front—8F1 (grey), circular, raised, umbonate, margins smooth and entire, reverse—8F2 (brownish-grey). Colonies on PCA after 10 days—26 × 26 mm, front—8F3 (greyish brown), margins smooth, regular and entire, circular, raised, reverse—8F1 (grey). Colonies on CMA after 10 days—25 × 25 mm, front—8E3 (greyish brown) in the periphery and 8F4 (dark brown) in the centre, circular, flat, margins smooth, regular and entire, reverse—8F3 (greyish brown).

Known distribution:—Tamhini Ghats, Maharashtra, India

Material examined:— INDIA. Maharashtra: Tamhini Ghats (18.4759º N ” 73.4592º E ”), from detritus rich soil, S.K. Singh, 10 February 2024, Ajrekar Mycological Herbarium, India ( AMH 10780 , holotype) ; ex-type culture deposited in National Fungal Culture Collection of India ( NFCCI-WDCM 932 ) NFCCI 5982 .

GenBank numbers:— ITS =PV029878, LSU =PV029879, Beta-tubulin=PV023970, TEF =PV023971

Notes:— S. laurentii is classified within the genus Scolecobasidium ( Sympoventuriaceae ) based on its macronematous and mononematous conidiophores, sympodial, cylindrical, denticulate conidiogenous cells, and solitary, dry conidia that are ellipsoidal in shape.

In the phylogenetic tree, S. laurentii clusters with S. ellipsoideum ( CBS 131796 and GUCC 18264), but it is morphologically distinct from S. ellipsoideum . Both species have ellipsoidal conidia, S. laurentii possesses longer conidiophores (8.63–120.59 µm) compared to S. ellipsoideum (7–16 µm).Additionally, S. laurentii forms indeterminate synnemata, which are compact to loosely arranged, as well as mono- to polyblastic conidiogenous cells. Its conidia bear appendages and displays unique features such as conidial anastomosis ( CAT) formation and catenated conidia. A comparative analysis of the 646 nucleotides inside the ITS (+ 5.8s) gene region of S. laurentii and S. ellipsoideum ( GUCC 18264) indicates 35 base pair discrepancies (5.41%), while analysis of 327 nucleotides in the tef1-α gene finds 7 base pair discrepancies (2.14%) between the two species. Significant base pair variations are enumerated in Table 3. Henceforth, a new species is established based on recommendations proposed by Jeewon and Hyde (2016).

Scolecobasidium laurentii is morphologically different from other related species including S. variabile , S. ellipsoideum , S. terreum , S. humicola , S. constrictum , and S. verruculosum ( Domsch et al. 1980) . The salient features presented in Table 4. Scolecobasidium laurentii differs from these taxa primarily in terms of conidial and conidiophore dimensions, as well as conidial septation.

Phylogenetic analysis

Phylogenetic analysis based on the combined sequence data from ITS, LSU, tef1-α, and tub-2 across 61 Scolecobasidium species confirmed that the current isolate represents a novel species as Scolecobasidium laurentii (NFCCI 5982) that clusters with S. ellipsoideum (CBS 131796 and GUCC 18264), supported by a high bootstrap value of 74.8% ( Figure 3 ).

The integrated sequence alignments of ITS, LSU, tef1-α, and tub-2 were employed to ascertain the phylogenetic position of the present isolate.The combined dataset comprised sequence data from 61 taxa. Of the 88 models evaluated, TIM3+F+I+G4 was determined as the best-fit model according to the Bayesian Information Criterion (BIC) and was chosen for further analysis. Phylogenetic reconstruction was conducted using the Maximum Likelihood method with this model. The log-likelihood value for the consensus tree was -31040.052. The estimated rate parameters were as follows: A-C: 0.80308, A-G: 1.88031, A-T: 1.00000, C-G: 0.80308, C-T: 3.55133, and G-T: 1.00000. Additionally, the proportion of invariable sites was 0.346, and the Gamma shape alpha was 0.749.

The combined phylogenetic analysis of ITS, LSU, tef1-α, and tub-2 confirmed that the present isolate formed a unique, distinct, and well-supported independent lineage within the phylogenetic tree.

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Figures

FIGURE 1. Scolecobasidium laurentii (AMH 10780; NFCCI 5782); a–b Colonies on PDA,front and reverse views.c–d Colonies on MEA, front and reverse views. e–f Colonies on PCA, front and reverse views. g–h Colonies on CMA, front and reverse views. i—Indeterminate synnemata on PDA(under stereomicroscope).j—Synnemata under high magnification.k–oVariable lengths of conidiophores (n—flexuous conidiophore). p–t—Mono- to polyblastic conidiogenous cells. u—Loop-like anastomosis in conidiophore. v—Conidial anastomosis (CAT) formation. w—Catenated conidia. x—Hyphae showing anastomosis. y—Conidial appendages. Scale bars: i–y = 20 μm.

FIGURE 2. Scolecobasidium laurentii (AMH 10780; NFCCI 5782); SEM images. a–c Parallel bundles of hyphae and conidiophores with denticulate conidiogenous cells (showing arrow). d—Scattered conidia. Scale bars: a, c = 2 μm, b,d = 10 μm.

FIGURE 3. Phylogenetic tree of Scolecobasidium laurentii inferred from Maximum likelihood (ML) analysis based on combined ITS, LSU, tub-2 and tef1-α sequences. Verruconis calidifluminalis CBS 125818 was used as outgroup. Numbers on the branches represent ML bootstrap. The proposed new species is highlighted.