Helminthosporium chiangraiense Boonmee, Huanraluek & K.D. Hyde, sp. nov.

Index Fungorum number: IF 558539; MycoBank number: MB 558539; Facesoffungi number: FoF 09192; Fig. 1

Etymology – The specific epithet “chiangraiense” refers to it discover in Chiang Rai Province.

Holotype – MFLU 21-0064

Saprobic on dead twigs. Sexual morph Undetermined. Asexual morph Hyphomycetous. Colonies 230–584 μm diam., effuse, dark brown to black, hairy. Mycelium immersed, forming stroma-like aggregations of dark brown pseudoparenchymatous cells. Conidiophores 168–304.5 × 5.5–12 (x̅= 232 × 9 μm, n = 20), mononematous, macronematous, caespitose, erect, cylindrical, straight to slightly flexuous, wide at the base, unbranched, dark brown, with apical pore, multi-septate, with dark scars, smooth-walled. Conidiogenous cells mono- to polytretic, integrated, terminal and intercalary, cylindrical, cicatrized, with dark scars, with distinct pores. Conidia 141–207 × 14–22 (x̅= 161 × 19 μm, n = 20), solitary, obclavate, straight to slightly curved, wider below than apex, truncate and with dark scar at base, upper cell tapering towards long apex, cylindrical, apically rostrate and pale brown, 9–13-distoseptate, smooth-walled. Conidial secession schizolytic.

Culture characteristics – Conidium germinating on PDA within 24 h and germ tubes produced from both ends. Colonies on PDA reaching 20 mm diam., in 7 days at room temperature, within a month covering the Petri dish, effuse, hairy, mycelium radiating outwards, fimbriate edge, dense, dark. Mycelium superficial and partly immersed, dark brown.

Material examined – THAILAND, Chiang Rai Province, Muang, Thasud, Mae Fah Lung University, Botanical garden, on dead twigs of unidentified plant, 14 June 2019, N. Huanraluek, CRB1 (MFLU 21-0064, holotype), ex-type living culture, MFLUCC 21-0087.

GenBank numbers – ITS=MZ538504, LSU=MZ538538.

Notes – Helminthosporium chiangraiense is phylogenetically related to H. leucadendri, but is clearly distinguished based on morphology and phylogeny. Phylogenetic analysis of the combined LSU, SSU and ITS sequence data of Helminthosporium taxa, our strain (MFLUCC 21-0087) clusters with the ex-type strain H. leucadendri (CBS 135133) with moderate support (0.95 BYPP; Fig. 2). Sequence comparison for the ITS region between H. chiangraiense (MFLUCC 21-0087) and H. leucadendri (CBS 135133) showed a 13.38% (76/568 bp) base pair difference (Jeewon and Hyde 2016). Helminthosporium chiangraiense is distinct from H. leucadendri in colony features and conidial shape, size and number of distosepta (Quaedvlieg et al. 2013). Therefore, we introduce Helminthosporium chiangraiense as a new species (Fig. 1).

Figure 1 – Helminthosporium chiangraiense (MFLU 21-0064, holotype). a Colonies on natural substrate. b Punctiform conidioma. c Cross section of conidioma. d Cross section of conidioma cells. e Conidiophores. f Conidiophore with attached conidium. g–l Conidia. m Germinated conidium. n, o Culture on PDA from surface and reverse. Scale bars: a=500 µm, b=200 µm, c, e=100 µm, d, f–m=50 µm

Figure 2 – Phylogram generated from maximum likelihood analysis based on combined LSU, SSU and ITS sequence data of Helminthosporium taxa (Massarinaceae) and related families. Seventy-seven strains are included in the combined analyses which comprise a total of 2567 characters. Cyclothyriella rubronotata (TR and TR9) are selected as the outgroup taxa. The best RAxML tree with a final likelihood value of − 11885.302979 is presented. RAxML analysis yielded 713 distinct alignment patterns and 23.08% of undetermined characters or gaps. Estimated base frequencies were as follows: A=0.246572, C=0.227244, G=0.274051, T=0.252133, with substitution rates AC=2.645156, AG=3.449326, AT=2.077592, CG=1.025293, CT=7.769520, GT=1.000000; gamma distribution shape parameter alpha=0.143346. Bootstrap support values for maximum likelihood (MLBS, left) equal to or greater than 70% is given above the nodes. Bayesian posterior probabilities (BYPP, right) equal to or greater than 0.95 are given above the nodes. Ex-type strains are in bold and newly generated sequence is in blue