Nigrospora tomentosae M. Luo, & J.W. Liu, sp. nov.

Index Fungorum number: IF 902096; Mycobank number: MB 902096; Facesoffungi number: FoF 15835 Fig. 1

Etymology – In reference to its host Citrus grandis cv. ‘Tomentosa’.

Endophytic on Citrus grandis cv. ‘Tomentosa’. Sexual morph: Not observed. Asexual morph: Conidiophores reduced to conidiogenous cells and aggregated in clusters on hyphae. Conidiogenous cells hyaline to pale brown, globose to pot-shaped or clavate, 9–12×5–7 μm, aseptate. Conidia 12–17 × 12–17 μm (x̄= 14.4 ± 1.5 × 14.1 ± 1.3, n=50), solitary, globose or subglobose, smooth, aseptate, dark brown to black. Chlamydospore thick-walled, rough surface, pale brown, subglobose to globose, 9–11×6–10 μm (x̄=9.8±0.7×8.1±1.2, n=50).

Culture characteristics – On PDA, colonies blanket, edge entire, off-white, reaching 9 cm diam after 7 d at 25 ℃, reverse pale yellow. On SNA, colonies flat, aerial mycelia dense with patches of sporulation, surface olive and reverse grey.

Material examined – China, Guangdong Province, Huazhou city, healthy fruit of Citrus grandis cv. ‘Tomentosa’, May 2021, B. Y. Cen, (MHKU 22-0173; holotype as dry culture), ex type ZHKUCC 22-0339 and living culture ZHKUCC 22-0340.

GenBank numbers – ITS=PP759659, tef1-α=PP763294, tub2=PP763296

Notes – Two strains representing N. tomentosae clustered in a well-supported clade with 76% ML bootstrap and 1.0 BYPP which is sister to N. camelliae-sinensis (Fig. 2). Morphologically, N. tomentosae differs from N. camelliaesinensis (Wang et al. 2017a, b) in its conidiogenous cells (9–12×5–7 μm vs. 6–11×4.5–8.5 μm). Also, N. tomentosae differs from N. pyriformis (Wang et al. 2017a, b) in conidial size (12–17×12–17 μm vs. 17.5–27.5×10–18.5 μm) and shape (globose or subglobose vs. water prop shapes). In pairwise nucleotide comparison, N. tomentosae is different from N. camelliae-sinensis (CGMCC 3.18125 Type) in 0.4% (2/513 bp) of tub2, and 1.7% (7/404 bp) of tef1-α.

Figure 1 – Nigrospora tomentosae (ZHKUCC22-0339, ex-type). a, b. Upper surface and reverse overview of culture 7d after inoculation on PDA medium; c. colony on SNA; d–g. conidiogenous cells giving rise to conidia; h, i. conidia. Scale bars: d–i=10 μm

Figure 2 – The best-scoring RAxML tree for the combined dataset of ITS, tub2 and tef1-α sequence data of Nigrospora following Chen et al. (2022a, b). The tree is rooted in Arthrinium malaysianum (CBS 102053). The matrix had 501 distinct alignment patterns with 13.35% undetermined characters and gaps. Estimated base frequencies were as follows; A=0.215381, C=0.290983, G=0.253160, T=0.240476; substitution rates AC=0.865842, AG=2.403689, AT=0.630710, CG=0.956682, CT=4.524366, GT=1.00000; gamma distribution shape parameter α=0.527542 with a final likelihood value of − 6763.967328. For the Bayesian inference, SYM+I+G model was selected for ITS, HKY+G for tub2, TPM2uf+I+G for tef1-α. Extype strains with T and newly generated sequences are in blue. Bootstrap supportvalues for ML equal to or greater than 50% and BYPP equal to or greater than 0.90 are given at the nodes