Pseudophaeocytostroma bambusicola Monkai & Phookamsak, sp. nov.
MycoBank number: MB 559821; Index Fungorum number: IF 559821; Facesoffungi number: FoF 12717;
Description
Saprobic on dead bamboo culms. Sexual morph: Undetermined. Asexual morph: Coelomycetous. Conidiomata 89–420 μm high, 250–704 μm diam., pycnidial, immersed in the clypeus, becoming raised, erumpent, penetrating on host surface, with small black dots of conidial masses,, hemispherical to subconical or lenticularis, uni- to bi-loculate, with an ostiole at the center, occasionally produced 2 ostioles in a locule, glabrous. Ostioles up to 80 μm wide, minutely papillate, immersed in host epidermis, circular. Conidiomatal wall up to 60 μm wide, consist of several layers of pseudoparenchymatous cells, arranged in a textura angularis, with dark brown outer layers and hyaline to pale brown towards the inner layers. Paraphyses 59–148 μm long × 2–3 μm wide (x̅ = 99 × 2 μm, n = 20), intermingled between conidiophores, broadly filiform, septate, hyaline, unbranched, obtuse at the apex, with small granules. Conidiophores 4–10× 2–5.5 μm (x̅ = 6 × 3 μm, n = 20), tightly aggregated, subcylindrical to ampulliform, or irregular in shape, septate, hyaline to pale brown, branched only at the base. Conidiogenous cells 8–12.5 × 2.5–3 μm (x̅ = 10 × 2 μm, n = 30), enteroblastic, phialidic, determinate, integrated, subcylindrical, tapering towards the apex, hyaline, smooth-walled. Conidia 9–13 × 3–4.5 μm (x̅ = 11 × 4 μm, n = 30), oblong to ellipsoid, obtuse at both ends, aseptate, brown, thick and smooth-walled.
Material examined: China, Yunnan Province, Honghe Autonomous Prefecture, Honghe County, Honghe Hani Rice Terraces, on dead bamboo culms, 26 January 2021, R. Phookamsak & S.C. Karunarathna , bn17 (KUN-HKAS 124569, holotype), ex-type living culture = KUMCC 22-XXXX; ibid., Honghe Autonomous Prefecture, Honghe County, Honghe Hani Rice Terraces, on dead bamboo culms, 26 January 2021, R. Phookamsak & S.C. Karunarathna, bn14 (KUN-HKAS KUN-HKAS 124568), living culture = KUMCC 22-XXXX
Distribution: China
Sequence data: KUMCC 22-XXXX (bn17), ITS: OP162724 (ITS1/ITS4); LSU: OP162722 (LROR/LR5); TEF1-α: OP139362 (728F/986R) KUMCC 22-XXXX (bn14), ITS: OP162725 (ITS1/ITS4); LSU: OP162723 (LROR/LR5); TEF1-α: OP139363 (728F/986R)
Notes: The nucleotide BLAST search of ITS sequence indicated that Pseudophaeocytostroma bambusicola (KUMCC XX-XXX, KUMCC XX-XXX) has the closest similarity with Phaeocytostroma sacchari strain CBS 275.34 with 96.26% similarity (Identities = 566/588, with 12 gaps), and is similar to Stenocarpella maydis strain Sm.A1-1, CBS 117558 (ex-epitype strain), CPC 16787, CPC 16786, CPC 16782, CPC 16781, CPC 16779, CPC 16778, CPC 16777 with 95.54% similarity (Identities = 552/579, with 5 gaps). The nucleotide BLAST search of LSU sequence indicated that Pseudophaeocytostroma bambusicola (KUMCC XX-XXX, KUMCC XX-XXX) has the closest similarity with Massariothea thysanolaenae strain MFLUCC 15-0452 (ex-type strain) with 99.64% similarity (Identities = 829/832, with no gap), and is similar to Phaeocytostroma ambiguum strain CBS 128561, CPC 17077, CPC 17076, CPC 17074, CPC 16776 with 99.64% similarity (Identities = 829/832, with one gap). The nucleotide BLAST search of TEF1-α sequence indicated that Pseudophaeocytostroma bambusicola (KUMCC XX-XXX, KUMCC XX-XXX) has the closest similarity with Phaeocytostroma sacchari strain CBS 275.34 with 88.86% similarity (Identities = 303/341, with 11 gaps), and is similar to P. ambiguum strain CFMS_1294, CPC 17071 (ex-epitype strain), CPC 16776, CPC 17075 CPC 17074, CPC 17072, CPC 16775 with 84.83% similarity (Identities = 179/211, with 12 gaps).
Pseudophaeocytostroma bambusicola is morphologically similar to Phaeocytostroma sacchari in having filiform paraphyses, aseptate, oblong to ellipsoid, brown, conidia with overlapping size (9–13 vs 9–14.5 μm) (Sutton 1964, 1980, TABLE 3). However, our new species differs from Phaeocytostroma sacchari in having uni- to bilocular conidiomata, minutely papillate ostiole with wider conidiomata (250–704 vs 350 μm) and not abundant, septate, longer paraphyses (59–148 vs 15–35 μm), while P. sacchari has abundant and aseptate paraphyses (Sutton 1964, 1980, TABLE 3). The host preference of P. sacchari is common on Saccharum sp., Sorghum sp. and Zea mays (Sutton 1964, Farr & Rossman 2022, TABLE 3), whereas our new species was found on bamboo.
In the phylogenetic analyses, Pseudophaeocytostroma bambusicola (KUMCC XX-XXX and KUMCC XX-XXX) formed a distinct subclade adjacent to Pseudophaeocytostroma sp. “sacchari” strains CBS 275.34, UMICH-1, km-1 and 135 with high support (98% ML/95% MP/1.00 PP, FIGURE 1). The pairwise nucleotide comparison of ITS and TEF1-α sequence data revealed significant differences (more than 1.5%) between Pseudophaeocytostroma bambusicola (KUMCC XX-XXX) and Pseudophaeocytostroma sp. “sacchari” strains CBS 275.34, km-1, UMICH-1 and 135 for each gene region (TABLE 2). The results of PHI test also supported the intraspecific variation among these strains and indicated the conspecific between strain UMICH-1 and km-1 (FIGURE 2). Thus, Pseudophaeocytostroma bambusicola was proposed as a new species based on morphological and phylogenetic evidence.
Phaeocytostroma sacchari was introduced and described by Sutton (1964). Lamprecht et al. (2011) firstly provided the sequence data for Phaeocytostroma sacchari, strain CBS 275.34 which isolated from Japan without a mention of host substrates and description provided. Carabez et al. (2014) isolated a fungus strain UMICH-1 from stalk rot symptoms of sugarcane in Mexico and identified it as Phaeocytostroma sacchari based on morphology and the high similarity of the ITS blast search. Whereas, two strains of Phaeocytostroma sacchari (km-1 and 135) were unpublished sequences from the GenBank. Thus, the morphological description is not available for these strains. Therefore, we treated these strains as Pseudophaeocytostroma sp. “sacchari” until their correct identification could be confirmed. The examination of ex-type or epitype specimens, more collection and additional sequences are needed for further studies on morphological and genetic variation in this group.