Roussoella sichuanensis W. H. Tian, K. Wu & Maharachch., 2023

Roussoella sichuanensis W. H. Tian, K. Wu & Maharachch. , sp. nov. ( FIG. 3 View FIGURE 3 )

MycoBank: MB 849137

Etymology: The species was named after Sichuan Province where the holotype of the fungus was collected.

Description: Saprobic on dead culms of bamboo. Asexual morph: Conidiomata 380–590 × 120–150 μm, pycnidial, forming under darkened, dome-shape areas on the host surface, conical or hemispherical with a flattened base, immersed under a clypeus, single to grouped, with a white central ostiole opening. Conidiomatal wall comprises several layers of cells of textura angularis to textura prismatica, with dark to brown outer thin layer 40–70 μm thick, black, and very thin at the base. Conidiophores reduced to conidiogenous cells. Conidiogenous cells 4.3–11.9 × 1.5–2.8 μm (x = 7.5 × 2.2 μm, n = 20) enteroblastic, indeterminate, discrete, unbranched, clavate or ampulliform to lageniform, hyaline, aseptate, smooth-walled. Conidia 3.8–4.8 × 2.4–2.8 μm (x = 4.4 × 2.6 μm, n = 20), oblong to ellipsoidal, with rounded to obtuse ends, initially hyaline, becoming brown, aseptate, verrucose, thick-walled. Sexual morph: the sexual form of this fungus is undetermined.

Culture characters: Colonies on PDA reaching 31.5 mm diam. in 10 days at 25 °C in the dark, circular, with even margin, white, cottony from above, and white at the margin, yellowish-brown at the center, floccose at the centre, covered with white hyphae; reverse greenish-brown.

Specimens examined: CHINA, Sichuan Province, Chengdu, Baiyungou , on dead culms of bamboo, 103°24′19″ E, 30°47′52″ N, 27 September 2021, WH Tian, BY 98_3 ( HKAS 129207 View Materials , holotype), ex-type culture UESTCC 23.0136 = CGMCC 3.25139 View Materials . GoogleMaps

Notes: Roussoella sichuanensis forms a sister clade to R. multiloculata and R. verrucispora with high statistical support. During the sequence comparisons between R. sichuanensis and R. multiloculata (GMBCC1056) , 12 bp differences (1.5%) were observed in a 790 bp fragment of ITS, and 12 bp differences (1.4%) were found in an 837 bp fragment of TEF1. Furthermore, in the sequence comparisons between our strain and R. verrucispora (CBS 125434), 12 bp differences (2.7%) were detected in a 444 bp fragment of ITS, 15 bp differences (1.8%) in an 837 bp fragment of TEF1, and 14 bp differences (1.6%) in an 898 bp fragment of RPB2. Roussoella sichuanensis is morphologically comparable to R. multiloculata , but differs in having a white central ostiole opening on the conidiomata and smaller conidia (3.8–4.8 × 2.4–2.8 μm vs. 4–5.5 × 2.5–3.7 μm) ( Dai et al. 2022). The asexual morph of R. verrucispora is unknown for the morphological comparison ( Liu et al. 2014). Therefore, based on the morphological differences and phylogenetic support, we introduce R. sichuanensis sp. nov. herein.