Pruniphilomyces circumscissus (Sacc.) Crous & Bulgakov, comb. nov.

MycoBank number: MB 835102; Index Fungorum number: IF 835102; Facesoffungi number: FoF 11206;  Fig. 49.

Basionym: Cercospora circumscissa Sacc., Fungi venet. nov. vel. Crit., Sér. 5: 189. 1878.

Synonyms: Passalora circumscissa (Sacc.) U. Braun [as ‘circumcissa’], Mycotaxon 55: 230. 1995. Mycosphaerella cerasella Aderh., Ber. dt. bot. Ges. 18: 246. 1900.

Leaf spots amphigenous, medium brown, with raised dark brown border, circular to irregular, 2–7 mm diam. Caespituli hypophyllous, fasciculate, forming an erumpent brown pseudoparenchymatal stroma, up to 60 µm wide, 30 µm high, bursting through stromata. Conidiophores subcylindrical, medium brown, thick-walled, finely verruculose, unbranched, straight to geniculate-sinuous, 1–2-septate, 25–50 ×   4–6 µm. Conidiogenous cells integrated, terminal and intercalary, subcylindrical with obtuse ends, brown, finely verruculose, 20–30 × 3–4 µm; with multiple round scars, thickened, darkened, with visible pore, 2 µm diam. Conidia (30–)55–65(– 70) × (3.5–)4(–5) µm, solitary, brown, thin-walled, guttulate, finely verruculose, gently curved or straight, obclavate, apex subobtuse, base obconically truncate, (2–)3(–4)-euseptate; hilum thickened and darkened, 2 µm diam. When sporulating in culture, conidiophores tend to be much larger, and also branched, but conidial dimensions are similar, with older conidia undergoing microcyclic conidiation.

Culture characteristics: Colonies erumpent, spreading, with moderate aerial mycelium and smooth, lobate margin, reaching 8 mm diam after 2 wk at 25 ºC. On MEA, PDA and OA surface and reverse olivaceous grey.

Typus: Russia, Rostov region, Shakhty city district, private orchard, on live leaves of Prunus cerasus (Rosaceae), 7 Oct. 2018, T.S. Bulgakov, HPC 2607 = Myc-52, CBS H-24226, culture CPC 36434 = CBS 145985.

Notes: Passalora circumscissa is a foliar pathogen of Prunus. It clusters apart from the type species of Passalora (P. bacilligera), and is sister to the genus Ragnhildiana (Videira et al. 2017) – see Fig. 3, part 2 and Fig. 8, part 2.

Based on a megablast search of NCBI’s GenBank nucleotide database, the closest hits using the ITS sequence had highest similarity to Passalora circumscissa (as Passalora sp., strain CHTA- 03, GenBank KT428056.1; Identities = 525/525 (100 %), no gaps), Paracercosporidium microsorum (as Mycosphaerella microsora, strain CBS 100352, GenBank EU167599.1; Identities = 522/537 (97 %), 3 gaps (0 %)), and Passalora arctostaphyli (strain CPC 22067, GenBank NR_155638.1; Identities = 521/536 (97 %), 2 gaps (0 %)). Closest hits using the LSU sequence are Ragnhildiana diffusa (strain CBS 106.14, GenBank MH866148.1; Identities = 861/862 (99 %), no gaps), Ragnhildiana pseudotithoniae (strain CBS 136442, GenBank NG_058049.1; Identities = 861/862 (99 %), no gaps), and Ragnhildiana pseudotithoniae (as Passalora pseudotithoniae, strain CPC 21688, GenBank KF777231.1; Identities = 861/862 (99 %), no gaps) – also see Fig. 3, part 2 and Fig. 8, part 2. Closest hits using the rpb2 sequence had highest similarity to Cercosporidium californicum (strain CPC 18390, GenBank MF951471.1; Identities = 488/580 (84 %), no gaps), Pantospora guazumae (strain CBS 130299, GenBank MF951556.1; Identities = 485/577 (84 %), no gaps), and Cercosporidium miurae (strain CPC 14643, GenBank MF951473.1; Identities = 487/580 (84 %), no gaps). The closest hit in the genus Ragnhildiana was with Ragnhildiana ferruginea (strain CBS 546.71, GenBank MF951645.1; Identities = 479/577 (83 %), no gaps).

Fig. 3, parts 1–4. Consensus phylogram (50 % majority rule) resulting from a Bayesian analysis of the Dothideomycetes LSU sequence alignment. Bayesian posterior probabilities (PP) > 0.79 are shown at the nodes and the scale bar represents the expected changes per site. Thickened branches represent PP = 1. Families and orders are indicated with coloured blocks to the right of the tree. GenBank accession and/or culture collection numbers are indicated for all species. The tree was rooted to Umbilicaria muehlenbergii (strain A18, GenBank JQ739997.1) and the species treated in this study for which LSU sequence data were available are indicated in bold face. A miniature overview tree is also presented to facilitate navigation along the tree topology.

Fig. 3. (Continued).

Fig. 3. (Continued).

Fig. 3. (Continued).

Fig. 8, parts 1, 2. Consensus phylogram (50 % majority rule) resulting from a Bayesian analysis of the Mycosphaerellaceae LSU/rpb2 sequence alignment (123 strains including the outgroup; 246 and 500 unique site patterns for LSU and rpb2, respectively; 35 928 sampled trees from 4 330 000 generations). The alignment is derived from the overview LSU/rpb2 alignment of Videira et al. (2017). Bayesian posterior probabilities (PP) > 0.79 are shown at the nodes and the scale bar represents the expected changes per site. Thickened branches represent PP = 1. Families are indicated with coloured blocks to the right of the tree. GenBank accession (superscript text) and/or culture collection numbers are indicated for all species. The tree was rooted to Cylindroseptoria ceratoniae (culture CBS 477.69; GenBank KF251655.1 and MF951419.1 for LSU and rpb2, respectively) and the species treated in this study are indicated in bold face.

Fig. 8. (Continued)

Fig. 49. Pruniphilomyces circumscissus (CPC 36434). A. Leaf spots on Prunus cerasus. B. Sporulation on SNA. C–E. Conidiophores and conidia in culture. F. Leaf spot. G, H. Stroma with conidiophores. I. Conidia. Scale bars = 10 µm.