Helminthosporiella stilbacea Konta & K.D. Hyde, sp. nov.

MycoBank number: MB 558312; Index Fungorum number: IF 558312; Facesoffungi number: FoF 09172, Figure 4.

≡ Cercospora palmicola f. stilbacea Moreau, Rev. Mycol. 12: 38. 1947 Nom. inval., Art.39.1 (Shenzhen)

≡ Helminthosporiella stilbacea Hern.-Restr., Sarria & Crous, in Crous et al., Persoonia 36:473.2016; Nom. inval., Art. 39.1 (Shenzhen)

≡Helminthosporium stilbaceum Moreau ex S. Hughes, Mycol. Pap.48: 38. 1952; Nom. inval., Art. 39.1 (Shenzhen).

≡Exosporium stilbaceum Moreau ex M.B. Ellis, Mycol. Pap.82: 38. 1961; Nom. inval., Art. 39.1 (Shenzhen).

≡Exosporium stilbaceum var. macrosporum Subramon. & V.G. Rao, Journal of the Annamalai University, part B, Sciences 29: 404. 1971; Nom. inval., Art. 35.1 (Shenzhen).

Saprobic on dead petiole of Cocos nucifera.Sexual morph: Undetermined. Asexual- morph: Colony on natural substrate black, hairy. Mycelium mostly immersed, at the sur- face forming small stroma-like aggregations of dark brown pseudoparenchymatous cells (6–)11–15(–25) µm diam (x = 14 µm). Conidiophores (60–)165–270(–310) × (5–)7–9(–12) µm (x = 200 × 8 µm, n = 30), macronematous, wide at the apex and base, arising singly from the stroma cells, erect, simple, unbranched, straight or flexuous, thick-walled, cylindrical, smooth-walled, dark brown, becoming pale brown at the apex, (4–)12–15-septate. Conidiogenous cells terminal and intercalary, polytretic, with well-defined thick, pale brown pores. Conidia (30–)45–60(–70) × 6–9 µm (x = 50 × 7 µm, n = 30), obpyriform to lageniform, straight or curved, smooth-walled, subhyaline to light brown, 5–8-distoseptate, with a thick scar at the base.

Culture characteristics: Culture on MEA, colony yellow-green at the center, turning dull green, pale yellow next, becoming dull green again, pale yellow, and white toward the margin. Colony smooth, dense at the middle, zonate, fluffy at the margin (Figure 4P).

Material examined: THAILAND, Prachuap  Khiri  Khan  Province,  on  dead  petiole of Cocos nucifera L. (Arecaceae), 30 July 2015, Sirinapa Konta PJK04gHB (MFLU 20-0521, holotype); ex-type living culture, MFLUCC 15-0813.

Notes: Crous et al. [63] introduced a new genus Helminthosporiella with a new combi- nation of Hel. stilbacea based on fresh collections from oil palm (Elaeis oleifera) in Colombia and the second collection of Hel. stilbacea was also collected from oil palm (Elaeis guineensis) in Brazil by Rosado et al. [64]. The full descriptions, illustrations, and sequence data are provided with interesting information as this species causes elliptical necrotic spots with a yellowish halo on living leaves of commercial oil palm plantations [63,64]. However, the type species was invalid because of the basionym lacked a Latin diagnosis [63]. From these, our fresh collection was collected from dead petiole of coconut (Cocos nucifera) and in phylogenetic analysis (Figures 1 and 2), three strains of Hel. stilbacea, including our strain, are grouped together with high bootstrap support. In this study, we therefore provide a holotype from our specimen, and introduce a new species Helminthosporiella stilbacea, complete with an English diagnosis, and validated by using the same name while linking to the valuable information provided from the previous publication of this species.

Figure 1. Comparison of the topology of Maximum likelihood majority rule consensus tree for the analyses of some selected Corynesporaceae, Massarinaceae, and Perioconiaceae isolates. (A) Phylogenetic tree of the dataset for ITS sequence data. (B) Phylogenetic tree of the dataset for LSU sequence data. Bootstrap support values for maximum likelihood (ML) equal to or higher than 50%, and Bayesian Posterior Probabilities (BYPP) equal to or greater than 0.90 are given above each branch. Novel taxa are in blue. Ex-type strains are in bold. The tree is rooted to Cyclothyriella rubronotata strains TR, TR9 (Cyclothyriellaceae).

Figure 2. Maximum likelihood majority rule consensus tree for the analyses of Massarinaceae and sister family Perioco- niaceae isolates based on a dataset of combined ITS, LSU, SSU, and tef1-α sequence data. Bootstrap support values for maximum likelihood (ML) equal to or higher than 50%, and Bayesian posterior probabilities (BYPP) equal to or greater than 0.90 are given above each branch. Novel taxa are in blue. Ex-type strains are in bold. The tree is rooted to Cyclothyriella rubronotata strains TR, TR9 (Cyclothyriellaceae).

Figure 4. Helminthosporiella stilbacea (MFLU 20-0521, holotype) (A) A coconut plantation in Prachuap Khiri Khan Province. Palm (C–E) Conidiogenesis. (F–H) Conidiophores (at red arrow are pores). (I–M) Conidia. (N,O) Germinated conidia. (P) Culture on MEA. Scale bars: B = 2 cm, C, I–O = 20 µm, D–H = 50 µm.