Pseudocercospora vernoniae Archana Singh & N.K. Dubey, sp. nov

Imdex Fungorum number: IF 834618; Mycobank Number: MB 834618, Facesoffungi number: FoF 07979, Figs. 1, 2

Etymology – Based to the host genus from which the taxon was isolated

Holotype – AMH:10043

Asexual morph: on leaf spots of Vernonia cineria, hypophyllous later amphiphyllous, 2–5 mm, angular, vein limited, discrete and later forming irregular larger patches, grayish brown on lower surface and dark blackish- brown on upper surface. Caespituli hypophyllous later amphiphyllous, dark brown, erumpent. Stromata substomatal, few cells to welldeveloped, made up of oval to round 3–5 µm wide pseudoparenchymatous cells, median to dark brown. Conidiophores fasciculate, unbranched or rarely branched, geniculate, 1–8-septate, light brown 13.6–40.3 (50)×3.5–5.5 µm. Conidiogenous cells integrated, polyblastic, cicaterised. Conidia septate (1–7), catenate in branched chains, straight to curved, cylindrical, constricted at septa, olivaceous brown, subcylindrical, base obclavate to obconico truncate, tip subacute to obtuse 21.7–44.8 (92)×4.5–5.5 µm. Sexual morph: Not observed.

Culture characteristics – Conidia germinating on Potato Dextrose Agar (PDA). Colonies very slow growing, velvety, greyish brown; reaching 2–5 mm diam., in 28 days at 27 °C, margin circular to irregular, reverse blackish brown raising centrally, of dense cottony mycelium and hard texture. Mycelium smooth, branched, asexual and sexual spores not formed within 60 days.

Material examined – India, Sonebhadra U.P., on living leaves of Vernonia cineria (L.) Less (Asteraceae), Dec 2017, AMH: 10043 (Holotype), culture ex type NFCCI: 4441.

GenBank numbers – MN691042 (LSU); MN691041 (ITS); MT106617 (act); MT106618 (tef1)

Notes – Pseudocercospora species are mostly host-specific (with few exceptions) related to a single host species, host genus or closely related host genera (Braun et al. 2013; Crous et al. 2013). Two species of Pseudocercospora has been reported earlier on Vernonia, Pseudocercospora cinereae (Deighton 1976) and Pseudocercospora vernoniacearum (Shukla et al. 1982). Pseudocercospora cineriae has dark brown circular, coalescing leaf spots and P. vernoniacearum has oval, effuse leaf spots whereas P. vernoniae has grayish brown, angular and vein limited leaf spots. Conidiophores are much smaller (14–40 µm) and more septate (1–8) in P. vernoniae compared to previously described species P. cinereae (1–3 septate, 40–150 ×3.5–5 µm) and P. vernoniacearum (44–133×3.5–5.4 µm). Conidia are simple and longer in P. cinereae (28.5–145×2.8–5.7 µm) and P. vernoniacearum (40–100×3.5–5.4 µm). The presence of catenate conidia in branched chains with smaller and variable in size 21.74– 44.76×4.5–5.5 µm) differentiate P. vernoniae from the previously described species. Molecular analysis based on combined gene analysis of LSU, ITS, act and tef1 (Fig. 3) reveals that P. vernoniae clusters with P. hakeae (CBS 144520) with moderate support.

Figure 1 – Pseudocercospora vernoniae (AMH: 10043, Holotype) a Habit of infected plant Vernonia cineria. b Symptoms on the upper leaf surface. c Symptoms on the lower leaf surface. d Culture after 3 weeks. e–o Conidia. k Conjugating conidia. p–q Fascicle of conidiophores. Scale bars: e–j=20 µm, k–o=10 µm

Figure 2 – Scanning Electron Micrographs of Pseudocercospora vernoniae. a Fasciles of conidiophores arising from stomata of the host plant. b Single fascicle of conidiophores. c Conidia attached to conidiophores. d Conidiogenous cells with scars. Scale bars: a–c=10 µm, d=2 µm

Figure 3  – Maximum likelihood tree illustrating the phylogeny of Pseudocercospora vernoniae with related species in Pseudocercospora based on LSU, ITS, act and tef1 concatenated sequences. Branches are labelled with ML and MP values≥50% and BYPP≥0.95 are indicated above the node respectively. The ex-types/reference strains are in bold; the new species is in blue. The tree is rooted with Pallidocercospora heimii (CPC:11716)