Oxydothis metroxylonicola Konta & K.D. Hyde, sp. nov., Index Fungorum number: IF 552539
Etymology: The specific epithet refers to the host genus Metroxylon and cola meaning loving.
Saprobic on petiole of Metroxylon sagu Rottb. (Arecaceae). Sexual morph: Ascomata 210–490 μm diam. (x̅ = 337 μm diam., n = 40, up to 700 μm), solitary or aggregated, mostly solitary when young, becoming grouped at maturity, immersed, comprising slightly raised blistering areas through the host tissue, axis oblique or perpendicular to the host surface, with central papilla, 62–110 μm high × 193–310 μm diam. (x̅ = 89 ×263 μm, n = 5), in transverse section, lenticular, globose to subglobose, darker at the central region, light towards the outer darker rim on the host surface. Peridium 15–36 μm (x̅ = 24 μm, n = 10) thick-walled, outer cells merging with the host epidermal cells, dark brown to black, walled cells of textura prismatica. Asci 137–150 × 13–19 μm (x̅ = 143 × 16 μm, n = 10), 8-spored, fasciculate, unitunicate, cylindrical-clavate, pedicellate, with a J+, wedge-shaped, subapical ring. Ascospores 52–58 × 8–9 μm (x̅ = 57 × 8 μm, n = 20), 2-seriate, fusiform, curved, tapering gradually from the center to the ends, centrally 1-septate, swollen at the central of each cell, not constricted at the septum, with pointed ends, hyaline, with large globose multi-guttules in each cell, smooth-walled. Asexual morph: Undetermined. Appressoria 12–23 μm high × 7–12 μm diam. (x̅ = 17 × 10 μm, n = 10), solitary, hyaline to light green, irregular in shape, thick-walled.
Culture characters: Ascospores germinating on MEA within 24 hours and germ tube was produced from end cell with developing appressoria structure. Colonies on MEA, olivaceous, rough on surface, produced ascomata-like, colony growing like double rings, hyphae, septate, branched, smooth.
Material examined: THAILAND, Krabi, on dead petiole of Metroxylon sagu (Arecaceae). 8 December 2014, S. Konta, KBR04c (MFLU 15-0027, holotype); ibid. (HKAS 95036, isotype); ex-type living culture, MFLUCC 15-0281.
Notes: Oxydothis metroxylonicola resembles O. elaeidis (Beeli) Sivan., O. parasitica and O. sabalensis (Cooke) Petr. in the shape of its ascospores. However, O. metroxylonicola differs from these species in having small, immersed ascomata, while O. elaeidis, O. parasitica and O. sabalensis have raised subglobose ascomata (ellipsoidal ascomata in O. sabalensis), and differently shaped ascospores (Sivanesan 1970, Fröhlich & Hyde 1994, Hyde 1994). Oxydothis parasitica is a pathogen causing leaf spot disease of Licuala ramsayi (Fröhlich & Hyde 1994). Phylogenetic analyses indicate that Oxydothis metroxylonicola is closely related to O. palmicola (87% ML, 0.99 PP), with O. calamicola as a basal clade without bootstrap support. Oxydothis metroxylonicola differs from O. calamicola and O. palmicola in having raised blistering ascomata on host surface, and differently shaped, J+, subapical rings.
Fig. Oxydothis metroxylonicola (holotype) a. Ascomata on host substrate. b–c. Close up of ascomata. d. Section of ascoma. e. Peridium. f–h. Asci. i–n. Ascospores. o. J+ reaction of apical ring in Melzer’s reagent. p. Germinating ascospore. q–v. Appressoria. Scale bars: a–b = 500 μm, c = 200 μm, d = 20 μm, e = 20 μm, f–n = 20 μm, o = 10 μm, p = 20 μm, q–v = 10 μm.