Cytospora sorbicola Norphanphoun, Bulgakov, T.C. Wen & K.D. Hyde, sp. nov., Index Fungorum number: IF552613

Etymology: The specific epithet “sorbicola” refers to the host plant genus Sorbus, on which the type specimens were collected.

Holotype: MFLU 15-2203

Associated with twigs and branches of Acer pseudoplatanus L. and Cotoneaster melanocarpus (Bunge) Loudon, Prunus cerasus L., Sorbus aucuparia L. and × Sorbaronia mitschurinii (Skvortsov & Maitul.) Sennikov. Sexual morph: Undetermined. Asexual morph: Conidiomata 850–1200 × 480–600 μm diameter, semi-immersed in bark, solitary, erumpent, with 1–2 locules, ostiolate. Ostioles 250–350 μm diameter, at the same level as the disc surface. Peridium comprising several layers of cells of textura angularis, with inner most layer thick, pale brown, outer later dark brown. Conidiophores unbranched, reduced to conidiogenous cells. Conidiogenous cells blastic, enteroblastic, phialidic, formed from the inner most layer of pycnidial wall, hyaline, smooth-walled. Conidia (4.4–)5.6–6.1 × 1.3–1.5(–1.6) μm (x̅ = 5.6 × 1.5 μm, n = 30), unicellular, elongate-allantoid, slightly curved, hyaline, smooth-walled.

Culture characteristics: Colonies on MEA, reaching 8 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, artificial forest, dead and dying branches on Acer pseudoplatanus (Sapindaceae), 18 June 2015, T. Bulgakov, T-499 (MFLU 15-2203, holotype, KUN, isotype), ex-type living culture, MFLUCC 16-0584, KUMCC; RUSSIA, Rostov Region, Rostov-on-Don City, Botanical Garden of Southern Federal University, parkland, on dead and dying branches on Sorbus aucuparia L. (Rosaceae), 30 May 2015, T. Bulgakov, T-472 (MFLU 15-2176, KUN), living culture, MFLUCC 16-0581, KUMCC; RUSSIA, Rostov Region, Rostov-on-Don City, Botanical Garden of Southern Federal University, Systematic Arboretum, on dead and dying branches on Cotoneaster melanocarpus (Bunge) Loudon (Rosaceae), 30 May 2015, T. Bulgakov, T-476 (MFLU 15-2180, KUN), living culture, MFLUCC 16-0582, KUMCC; RUSSIA, Rostov Region, Krasnosulinsky District, Donskoye forestry, old orchard, on dead and dying branches on Sorbaronia mitschurinii (Skvortsov & Maitul.) Sennikov (Rosaceae), 18 June 2015, T. Bulgakov, T-501 (MFLU 15-2205, KUN), living culture, MFLUCC 16-0585, KUMCC; RUSSIA, Rostov Region, Krasnosulinsky District, Donskoye forestry, artificial forest platation, forest nursery, dead and dying branches on Prunus cerasus L. (Rosaceae), 18 June 2015, T. Bulgakov, T-502 (MFLU 15-2206, KUN), living culture, MFLUCC 16-0586, KUMCC; RUSSIA, Rostov Region, Krasnosulinsky District, Donskoye forestry, Kabanya Balka (Boar gully), steppe on slope of gully, dying twigs and branches (necrotrophic) on Cotoneaster melanocarpus Lodd., G. Lodd. & W. Lodd., 27 October 2015, T. Bulgakov (MFLU 15-3768, KUN), living culture, MFLUCC 16-0633, KUMCC.

Notes: Six collections of Cytospora sorbicola (MFLUCC 16-0581, MFLUCC 16-0582, MFLUCC 16-0584, MFLUCC 16-0585, MFLUCC 16-0586, MFLUCC 16-0633) were made. Cytospora sorbicola is similar to C. donetzica and C. ceratosperma (Tode) G.C. Adams & Rossman in conidia size (5.6 × 1.5 μm, 5.5 × 1.4 μm, 5–6 × 1.4 μm, respectively) (Saccardo 1884), but C. donetzica differs in having multiloculate conidiomata and shorter ostiolar necks (150–250 μm). Phylogenetic analysis (Figs. 1 and 2) place C. sorbicola in a separate clade from C. ceratosperma which is sister to C. donetzica (MFLUCC 16-0574, MFLUCC 15-0864, MFLUCC 16-0589, MFLUCC 16-0641) with bootstrap support (86% MP/ 76% ML/ 0.98 PP). Cytospora sorbicola differs from C. donetzica with five ITS polymorphisms, 23 RPB2 polymorphisms and seven ACT polymorphisms.

FIG: Cytospora sorbicola on Acer pseudoplatanus (MFLU 15-2203, holotype). a Stromatal habit in wood. b Fruiting bodies on substrate. c Surface of stroma. d Vertical section of the stroma showing conidiomata. e Peridium. f Ostiolar neck. g–i Conidiogenous cells with attached conidia. j Mature conidia. k Germinating spore. l, m Colonies on MEA (l-from above, m-from below). Scale bars: a = 2000 μm, b, c = 500 μm, d = 200 μm, e = 50 μm, f = 100 μm, g, h, i, j = 5 μm, k = 10 μm.