Thyrostroma ulmeum Senwanna, Bulgakov & K.D. Hyde, sp. nov.
Index Fungorum number: IF557793
Etymology – Named after the host genus on which it occurs, Ulmus.
Associated with canker on twigs of hybrid elm Ulmus minor × Ulmus pumila. Asexual morph: Colonies effuse, partly immersed, stromatic, erumpent through host epidermis, pulvinate to applanate, black, velvety, with lenticular or irregularly dehiscent openings. Sporodochia up to 500 µm diam., with pseudoparenchymatous basal stroma. Conidiophores (29–) 40–56 (–82) × 8–11 (–13) µm (x̅ = 51.5 × 10.6 μm, n = 16), macronematous, erect, compactly packed, septate, branched, hyaline to pale brown, smooth. Conidiogenous cells (20–) 22–34 (–39) µm long, enteroblastic, annellidic, with 1–2 annellations, integrated, terminal. Conidia (40–) 44–58 (–63) × 14–21 µm (x̅ = 51.8 × 17.7 μm, n = 50), acrogenous, fusiform to obclavate or obpyriform, pale to dark brown, truncate at base, 3–6(–8) µm diam., rounded at apex, 3–5-transverse septate, with longitudinally 0–1-septate, rough-walled, minutely echinulate. Sexual morph: Undetermined.
Material examined – Ukraine, Donetsk region, Donetsk Botanical Garden, trees near pond, on dead twigs of hybrid elm Ulmus minor × Ulmus pumila (Ulmaceae), 20 May 2017, T.S. Bulgakov, DNK117 (MFLU 17-2538, holotype).
GenBank submissions – ITS: MT627476, LSU: MT627478, TEF1-α: MT614250.
Known distribution (based on molecular data) – Ukraine (this study).
Known hosts (based on molecular data) – Ulmus minor × Ulmus pumila (this study).
Notes – Thyrostroma ulmeum is similar to Dothidotthia species and Wilsonomyces species in conidial shape (Marin-Felix et al. 2017, Senwanna et al. 2019a). However, Thyrostroma and Dothidotthia have holoblastic, monoblastic, or annellidic, percurrently proliferating conidiogenous cells, whereas Wilsonomyces has holoblastic, sympodially proliferating conidiogenous cells. In addition, Thyrostroma ulmeum differs from Dothidothia in having longer conidia and a different number of transverse and longitudinal septa. Based on the NCBI BLASTn search of LSU and ITS sequence data, closest matches for Thyrostroma ulmeum are Dothidotthia negundinicola (CBS 145039 98% similarity) and Thyrostroma cornicola (CPC 25427 96% similarity) respectively. Phylogenetic analyses based on a combined LSU, SSU, ITS and TEF1-α sequence data (Fig. 5) reveal that Thyrostroma ulmeum forms a sister lineage with T. tiliae and groups with T. ulmigenum. Thyrostroma ulmeum is easily distinguished from T. tiliae and T. ulmigenum by the conidial shape.