Helicoma oleifera Y. R. Xiong, Manawas. & K. D. Hyde sp. nov.

Fig. 2

Etymology.

Species epithet refers to the host species name “ oleifera ” from which the fungus was isolated.

Holotype.

MHZU 23-0157.

Description.

Saprobic on the rotting petiole of Elaeis oleifera. Sexual morph: Not observed. Asexual morph: Hyphomycetous, helicosporous. Colonies on the substratum superficial, effuse, gregarious, brown. Mycelium composed of partly immersed, partly superficial, hyaline, septate, branched hyphae. Conidiophores 145–360 µm long, 6.5–7.5 µm wide (x ̄ = 210 × 6.5 μm, n = 20), macronematous, mononematous, cylindrical, unbranched or branched at base, straight to slightly bent, septate, deep brown at root part, brown at apex, pale brown at middle part mixing with some brown areas, smooth-walled with irregular inclusion. Conidiogenous cells 13–22 µm long, 5–7.5 µm wide (x ̄ = 17 × 6.4 μm, n = 20), monoblastic, integrated, sympodial, terminal, cylindrical or fertile at the apex of conidiophores, brown, smooth-walled with irregular inclusion; with denticles, 1.3–2.3 µm long, 1.4–2.5 µm wide (x ̄ = 1.6 × 1.8 μm, n = 20), arising from the apex portion of conidiophores as tooth-like and papillate protrusions, exposed or imbedded in the apex of conidiophore, mono- to polyblastic, brown, smooth-wall. Conidia 18–22.5 μm diam. (x ̄ = 20.4 μm, n = 40) and conidial filament 6.8–9 μm wide (x ̄ = 8.2 μm, n = 40), 45–55 μm long (x ̄ = 50.6 μm, n = 40), solitary, acrogenous, helicoid, rounded at tip, tapering towards flat end, conic truncate at base, tightly coiled 1 ½ times, 8 - septate, not becoming loose in water, guttulate, hyaline to pale brown, smooth-walled, the third cell shrinking and producing the root canal.

Culture characteristics.

Conidia germinating on water agar and germ tubes produced from conidia within 12 h. Colonies growing on PDA attaining 2.5 cm diam. after six weeks at 25 ° C, irregular, undulate, rough, superficial and partially immersed, brown aerial mycelium mixed with pale brown, deep brown at up and down junction area; reverse brown with pale brown.

Material examined.

China, Yunnan Province, Xishuangbanna City, an unidentified forest beside National Highway 219 (21 ° 93 ' N, 101 ° 24 ' E, 549.6 m elev.), rotting petiole of the Elaeis oleifera, 5 February 2023, Y. R. Xiong and Li Lu, XG 198 (MHZU 23-0157, holotype); ex-type culture, ZHKUCC 24 -0121, other living cultures ZHKUCC 24-0122, ZHKUCC 24-0766, ZHKUCC 24-0767.

Notes.

Four isolates obtained in this study from the rotting petiole of the Elaeis oleifera clustered in an independent clade in the phylogenetic tree with 78 % ML, 76 % MP bootstrap support and 1.00 BIPP bootstrap support. The nucleotide differences between Helicoma oleifera and its phylogenetically related species were checked, excluding gaps: H. acropleurogenum (GZCC 22-2035) - ITS: 3.53 % (18 / 510 base pairs), LSU: 0.71 % (6 / 844 base pairs), tef 1 - α: 2.85 % (26 / 912 base pairs), rpb 2: 3.92 % (41 / 1045 base pairs); H. dennisii (NBRC 30667) - ITS: 4.36 % (25 / 573 base pairs), LSU: 0.35 % (2 / 564 base pairs), tef 1 - α and rpb 2 sequence unavailable; H. hydei (MFLUCC 18-1270) - ITS: 3.50 % (26 / 744 base pairs), LSU: 0.71 % (6 / 847 base pairs), tef 1 - α: 2.74 % (25 / 912 base pairs), rpb 2 sequence is unavailable; H. inthanonense (MFLUCC 11-0003) - ITS: 4.56 % (26 / 570 base pairs), LSU: 1.63 % (14 / 860 base pairs), tef 1 - α and rpb 2 sequence is unavailable. Helicoma oleifera is different from related species not only in the size of conidia and conidiophores (Table 3), but also in conidia, which shrink and produce the tubular structure at the third cell (Fig. 2 q, r, s), while other species do not produce any deformation. In addition, H. acropleurogenum (Lu et al. 2023) has intercalary and mostly monoblastic, rarely polyblastic conidiogenous cells; however, H. oleifera has terminal and monoblastic or polyblastic conidiogenous cells. Helicoma dennisii (Tsui et al. 2006) has intercalary and polyblastic conidiogenous cells and fertile denticle structure at several cells on the upper end of the conidiophore. However, H. oleifera only has fertile denticle structures at the apex cell of the conidiophore. Furthermore, H. oleifera differs from H. hydei (Liu et al. 2019) by having an embedded denticle structure, while H. hydei (Liu et al. 2019) has an exposed denticle structure. Furthermore, H. inthanonense (Boonmee et al. 2011) has acropleurogenous and brown conidia with 7 - septate and produces an asexual morph from MEA culture, while H. oleifera has acrogenous and hyaline to pale brown conidia with 8 - septate. Therefore, we introduce H. oleifera as a new species.