Cytospora rusanovii Norphanphoun, Bulgakov, T.C. Wen & K.D. Hyde, sp. nov., Index Fungorum number: IF552609

Etymology: The specific named after the Russian mycologist Victor Andreyevich Rusanov, researcher of plant pathogenic fungi in Rostov region of Russia.

Holotype: MFLU 15-1931

Associated with twigs and branches of Salix babylonica L. and Populus × sibirica G.V. Krylov & G.V. Grig. ex A.K. Skvortsov [P. balsamifera L. × P. nigra L.]. Sexual morph: Undetermined. Asexual morph: Conidiomata 530–800 × 280–350 μm diameter, semi-immersed in host tissue, solitary, scattered, erumpent, discoid, circular to ovoid, with 1–3 locules, and long ostiolar neck. Ostioles 155–170 μm diameter, at the same level as the disc surface. Peridium comprising several layers of cells of textura angularis, with inner most layer thick, dark brown, outer layer dark brown to black. Conidiophores unbranched, reduced to conidiogenous cells. Conidiogenous cells blastic, enteroblastic, phialidic, formed from the inner most layer of pycnidial wall, hyaline, smooth-walled. Conidia (6–)6.5–7.1 ×1.4–1.5(–1.6) μm (x̅ = 6.7 × 1.5 μm, n = 30), unicellular, elongate-allantoid, 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, Shakhty City, Central Park, parkland, on dying branches of Salix babylonica (Salicaceae), 8 July 2015, T. Bulgakov (MFLU 15-1931, holotype, KUN, isotype), ex-type living culture, MFLUCC 15-0854, KUMCC; RUSSIA, Rostov Region, Shakhty City, Central Park, parkland, on dying branches of Populus × sibirica G.V. Krylov & G.V. Grig. ex A.K. Skvortsov [P. balsamifera L. × P. nigra L.] (Salicaceae), 9 July 2015, T. Bulgakov (MFLU 15-1929, KUN), living culture, MFLUCC 15-0853, KUMCC.

Notes: The new species has semi-immersed, 1–3-loculate conidiomata, with long ostioles and 6.7 × 1.5 μm, unicellular conidia. Cytospora rusanovii is most similar to C. microspora Rabenh. in conidia size (6–7 × 1–1.3) (Saccardo 1884). However, C. microspora differs from C. rusanovii in having multi-loculate conidiomata (>10 locules) (Corda 1839).
Phylogenetic analyses of ITS and multi-gene sequence data indicate that Cytospora rusanovii can be distinguished from C. curvata (MFLUCC 15-0865) and other species in Cytospora, with 98% bootstrap support and 1.00 Bayesian posterior probability in MP, ML and BI analyses, while the polymorphic nucleotides differences are discussed under C. curvata.

FIG: Cytospora rusanovii on Salix babylonica (MFLU 15-1931, 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 Ostioles. 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 = 1000 μm, c = 500 μm, d = 100 μm, e = 10 μm, f = 20 μm, g, h, i, j = 5 μm, k = 50 μm.