Cytospora sorbi Norphanphoun, Bulgakov, T.C. Wen & K.D. Hyde, sp. nov., Index Fungorum number: IF552612

Etymology: The specific epithet “sorbi” refers to the host plant genus Sorbus, on which the type specimen was first collected.

Holotype: MFLU 15-3781

Associated with twigs and branches of Sorbus aucuparia L. Sexual morph: Undetermined. Asexual morph: Conidiomata 900–1200 × 420–550 μm diameter, semi-immersed in host tissue, scattered, erumpent, with 3–4 locules, and ostiolar neck. Ostioles 250–300 μm diameter, at the same level as the disc surface. Peridium comprising a few to several layers of cells of textura angularis, with inner most layer thick, brown, outer dark brown. Conidiophores unbranched or occasionally branched at the base, reduced to conidiogenous cells. Conidiogenous cells blastic, enteroblastic, phialidic, formed from the inner most layer of pycnidial wall, hyaline, smooth-walled. Conidia (6–)6.4–7.6 × 1.4–1.5(–1.8) μm (x̅ = 6.5 × 1.5 μm, n = 30), unicellular, elongate-allantoid, hyaline, smooth-walled.

Culture characteristics: Colonies on MEA, reaching 5 cm diameter after 7 days at 25 °C, producing dense mycelium, circular, margin rough, white, lacking aerial mycelium.

Material examined: RUSSIA, Rostov Region, Krasnosulinsky District, Donskoye forestry, dying twigs and branches on Sorbus aucuparia (Rosaceae), 27 October 2015, T. Bulgakov, T-1119 (MFLU 15-3781, holotype, KUN, isotype), ex-type living culture, MFLUCC 16-0631, KUMCC.

Notes: Cytospora sorbi was collected from Sorbus aucuparia. In phylogenetic analysis C. sorbi forms a separate branch as a sister taxon to C. sorbicola and C. donetzica. Cytospora sorbicola and C. donetzica differs from C. sorbi in having smaller conidia (5.6 × 1.5 μm, 5.5 × 1.4 μm, 6.5 × 1.5 μm, respectively).
In ITS, Cytospora sorbi differs from C. sorbicola in eleven polymorphisms and eight polymorphisms from C. donetzica. In RPB2 it differs from C. sorbicola with 20 polymorphisms and 28 polymorphisms from C. donetzica. In ACT, it differs from C. sorbicola with nine polymorphisms and eight polymorphisms from C. donetzica.

FIG: Cytospora sorbi on Sorbus aucuparia L. (MFLU 15-3781, holotype). a Stromatal habit in wood. b Fruiting bodies on substrate. c Surface of fruiting bodies. d Cross section of the stroma showing conidiomata. e Peridium. f Ostiolar neck. g–h Conidiogenous cells with attached conidia. i Mature conidia. j Germinating spore. k, l Colonies on MEA (k-from above, l-from below). Scale bars: a = 2000 μm, b = 1000 μm, c = 500 μm, d = 500 μm, e = 50 μm, f = 200 μm, g = 10 μm, h = 10 μm, i = 10 μm and j = 40 μm.