Trichoderma fulviclavum G. S. Jin & Z. X. Zhu sp. nov.

Figs 5, 6

Etymology.

The epithet fulviclavum refers to the fulvous (yellow-brown) clavate stromata produced by this species.

Diagnosis.

Stromata clavate, brown to light brown, without color change in 3 % KOH; ascospores hyaline, monomorphic; asexual morph extremely slow-growing, producing brown pigment and chlamydospores, but lacking conidiation.

Typification.

China • Jilin Province, Changchun City, Shuangyang District, 43°21'3"N, 125°53'42"E, 356 m alt., on pine branches, 31 Jul. 2025, Z. X. Zhu, G. S. Jin, B. Liang, M. Y. Zhu, G. L. Zhao 2191 (Holotype HMJAU 34754, ex-type culture CGMCC 7.673).

Sexual morph.

Fresh stromata are similar to dry stromata in morphology. Dry Stromata cylindric or flattened clavate, often aggregate and grow into palmate bunches. Length up to 57 mm, 12–15 mm diam. White and hairy when young, turning light brown when mature, not changing color in KOH. Stroma surface young with fur, turns plane when mature, smooth or slightly wrinkled, perithecial protuberances not evident, ostioles appearing as black or brown dots.

In section stroma, perithecia flask-shaped, elliptical or globose (83 –) 93–193 (– 207) × 75–170 (– 193) µm (n = 30). Ostioles (30 –) 39–57 (– 62) µm long (n = 20), 17–35 (– 40) µm wide at the apex (n = 20). Peridium brown, (6.3 –) 7.4–8.2 (– 9.1) µm wide at the base and sides (n = 20). Cortical tissue of textura angularis, cells hyaline, thick-walled, (2.8 –) 3.9–5.9 × (1.6 –) 2–4.1 (– 4.6) μm (n = 20); subcortical tissue of textura angularis mixed with textura intricata, cells hyaline, thin-walled, 4.4–8 (– 10.2) × 3.1–4.3 (– 4.8) μm (n = 20), hyphae hyaline, thin-walled, 1.8–4.4 μm wide (n = 20); subperithecial tissue of textura epidermoidea, cells hyaline, thin-walled, 3.5–8 (– 11) μm wide (n = 20); tissue at the base of textura intricata, cells hyaline, thin-walled, 3.9–8.1 μm wide (n = 20). Asci 60–75 (– 80) × (2.8 –) 3.2–4.4 µm (n = 20). Ascospores monomorphic, hyaline, verruculose, cells subglobose to globose, 2.6–3.9 × 2.4–3.5 µm (n = 30), l / w 0.9–1.1 (– 1.3).

Cultures and asexual morph.

On PDA at 25 ° C, colony radius 1–3 mm after 72 h, the plate fully covered after 3 weeks. Colonies initially white, gradually turning brown with age, with aerial hyphae densely developed at the colony base; exudate droplets present on aerial hyphae, small, light brown to brown, and evenly distributed. After 30 days, chlamydoconidia observed, brown, globose to subglobose, sessile on hyphae, (3 –) 3.3–10.7 (– 11.9) × (3.5 –) 3.9–11.3 (– 12.3) µm (n = 30), l / w 1–1.3 (– 1.5). Conidiophores and conidia not observed. Odor absent; brown pigment present.

On CMD at 25 ° C, colony radius 1–2 mm after 72 h, with the plate fully covered after 4 weeks. Colonies white, forming a dense concentric annular pattern, with rare aerial hyphae. Conidia and chlamydospores not observed after 4 weeks. Odor absent; brown pigment present.

On SNA at 25 ° C, colony radius 1–2 mm after 72 h, reaching 34–37 mm after 40 days. Colonies white, faint, forming a dense concentric annular pattern, without aerial hyphae. Conidiation not observed after 40 days. Odor absent; brown pigment present.

Additional specimens examined.

China • Jilin Province, Changchun City, Shuangyang District, 43°21'3"N, 125°53'41"E, 365 m alt., on pine branches, 31 Jul. 2025, Z. X. Zhu, G. S. Jin, J. Ji, G. L. Zhao, X. Z. Li 2196, HMJAU 34758, ex-type culture HMJAU 34759.

Notes.

Trichoderma fulviclavum is characterized by clavate stromata, extremely slow vegetative growth, absence of conidiation, and the production of brown chlamydoconidia. Morphologically, it resembles clavate-stromatic species such as T. alutaceum, T. leucopus, T. seppoi, and T. clavaticapitatum, all of which share the absence of a color change in 3 % KOH (Jaklitsch 2011). In its asexual morph, T. fulviclavum exhibits an exceptionally slow growth rate on PDA (1–3 mm after 72 h), comparable to members of the Psychrophilum clade, including T. psychrophilum (<1 mm after 72 h), T. rhododendri (4–5 mm after 72 h), T. balearicum (19–22 mm after 72 h), T. crystalligenum (8–10 mm after 72 h), T. calamagrostidis (9–16 mm after 72 h), and T. oligosporum (9–12 mm after 72 h) (Jaklitsch 2011; Zhu and Zhuang 2015; Zeng et al. 2024). Conidia were not observed in T. fulviclavum, similar to T. rhododendri; instead, chlamydoconidia were observed to be sessile on hyphae, a rarely reported character in Trichoderma.

Phylogenetically, T. fulviclavum clusters closely with T. rhododendri (CBS 119288) and T. psychrophilum, whereas it is distantly related to T. leucopus, T. alutaceum, and other clavate-stromatic species; detailed morphological distinctions are provided in Table 3. Notably, clavate stromata have not previously been reported in the Psychrophilum clade.