Pseudocercospora tabei Y.Meswaet, Mangelsdorff, Yorou & M.Piepenbr., 2021

Meswaet, Yalemwork, Mangelsdorff, Ralph, Yorou, Nourou S. & Piepenbring, Meike, 2021, Unravelling unexplored diversity of cercosporoid fungi (Mycosphaerellaceae, Mycosphaerellales, Ascomycota) in tropical Africa, MycoKeys 81, pp. 69-138 : 69

Pseudocercospora tabei Y.Meswaet, Mangelsdorff, Yorou & M.Piepenbr. sp. nov. Figs 14I , 21

Type.

Benin. Borgou: Parakou , c. 360 m a.s.l., 9°20'07"N, 2°38'50"E, on Vigna unguiculata (L.) Walp. ( Fabaceae ), 2 Sep 2019, Y. Meswaet and A. Tabé, YMM220 (Holotype: M-0312678; Isotype: UNIPAR). Ex holotype sequences. MW834450 (SSU), MW834434 (LSU), MW834439 (ITS), MW848617 (tef1) .

Etymology.

The epithet Pseudocercospora tabei refers to the person who collected the type specimen, Affoussatou Tabé, mycologist at the University of Parakou, Benin.

Diagnosis.

Pseudocercospora tabei differs from other Pseudocercospora spp. known on Vigna spp. by external hyphae, well-developed stromata, as well as the sizes of conidiophores [(20.5-)24-82(-84.5) × 3-4(-4.5) μm] and conidia [(20.5-)24-82(-84.5) × 3-4(-4.5) μm] (Table 7 ).

Description.

Leaf spots amphigenous, subcircular to irregularly angular, 2.5-7.5 mm diam., occasionally limited by veins, yellowish brown to pale brown, reddish brown to dark brown when old, more evident on the adaxial surface of the leaves, margin indefinite. Caespituli amphigenous, brown. Mycelium internal and external. External hyphae branched, 2-2.5(-3.5) μm wide, septate, olivaceous brown to brown, smooth. Stromata lacking or formed by few aggregated swollen hyphal cells to well-developed, up to approx. 45 μm diam., immersed in the mesophyll or in substomatal chambers, globular to irregular, brown to mostly dark brown. Conidiophores in small, loose to moderately dense fascicles arising from stromata, breaking through the adaxial epidermis of the leaves or penetrating through stomatal openings, or solitary, arising from external hyphae, straight to sinuous or somewhat geniculate, simple or rarely branched, (11.5-)14.5-40(-44.5) × (3-)3.5-4(-4.5) μm, 0-4-septate, smooth, olivaceous brown to brown, paler towards the tips, sometimes a conidiophore is reduced to a single conidiogenous cell. Conidiogenous cells terminal or lateral, rarely up to 20 μm long, pale or olivaceous brown, smooth, proliferating sympodially; loci 2-3.5 μm wide, not thickened and not darkened. Conidia solitary, narrowly cylindrical to obclavate-cylindrical, straight to slightly curved, (20.5-)24-82(-84.5) × 3-4(-4.5) μm, conspicuously 2-6(-8)-septate, olivaceous brown, smooth, apex subacute to rounded and narrower than the rest of the conidium, base truncate, (2-)2.5-3.5 µm wide, hila not thickened and not darkened.

Additional specimens examined.

Benin. Borgou: Parakou , c. 354 m a.s.l., 9°20'02"N, 2°38'48"E, on Vigna unguiculata , 27 Aug 2019, Y. Meswaet and A. Tabé, YMM232A (Paratypes: M-0312679; UNIPAR) . Benin. Borgou: Parakou , c. 391 m a.s.l., 9°22'56"N, 2°37'33"E, same host, 29 Aug 2019, Y. Meswaet and A. Tabé, YMM232B (M-0312680) .

Herbarium specimens examined for comparison.

Pseudocercospora cruenta . On Vigna unguiculata : USA. Mississippi: Starkville, Sep 1888, Tracy S. M. s.n. (BPI 435817 Paratype of Cercospora dolichi ). On Phaseolus sp.: USA. South Carolina: Aiken, Ravenel H. W. s.n (BPI 439619, type of C. phaseolorum ). Pseudocercospora stizolobii . On Mucuna sp.: Philippines. Los Baños, 6 Apr 1913, Raimundo M. B. 892 (BPI 441666, Holotype of C. stizolobii ) .

Host and distribution.

On Vigna unguiculata ( Fabaceae ) in Benin.

Notes.

On species of Vigna , eight species of Pseudocercospora , namely Ps. cruenta , Ps. mungo Deighton, Ps. phaseolicola Goh & W.H. Hsieh, Ps. shihmenensis (J.M. Yen) J.M. Yen, Ps. vexillatae (J.M. Yen) U.Braun, Ps. vignae-reticulatae Deighton, Ps. vignicola (J.M. Yen, A.K. Kar & B.K. Das) U.Braun and Ps. vignigena J.M. Yen, A.K. Kar & B.K. Das are known ( Farr and Rossman 2021). Among these species, Ps. mungo described on Vigna radiata , V. mungo from Tanzania (East Africa) ( Deighton 1976) and Ps. phaseolicola on Vigna radiata from China and Taiwan ( Hsieh and Goh 1990) are morphologically similar to the present Pseudocercospora specimen from Benin (Table 7 ). Based on the original description by Deighton (1976), Ps. mungo , however, differs from the present species in causing leaf spots that form only indefinite chlorotic areas on the adaxial surface, hypophyllous caespituli, lack of external hyphae and above all, by longer and wider conidiophores [up to 90(-130) × 4.5-7.5 µm)] and wider conidia (4.5-7.5 µm) ( Deighton 1976). Ps. tabei causes yellowish brown to pale brown leaf spots, that are reddish brown to dark brown, when old, forms amphigenous caespituli, often produces well developed stromata, external hyphae and above all, shorter and narrower conidiophores [(11.5-)14.5-40(-44.5) × (3-)3.5-4(-4.5) µm] and narrower conidia (3-4 μm). Ps. phaseolicola differs by producing hypophyllous caespituli, no stromata, non-fasciculate, olivaceous, shorter and narrower conidiophores [3-25 × 1.5-3 µm versus (11.5-)14.5-40(-44.5) × (3-)3.5-4(-4.5) µm in Ps. tabei ] and narrower conidia [1.5-2 µm versus 3-4 µm in Ps. tabei ] ( Hsieh and Goh 1990).

In the multi-gene phylogeny (Fig. 1 ), Ps. tabei forms part of a polytomy with a large genetic distance (branch length) in relation to other sequences considered in the analysis. In the tef1 phylogeny, Ps. tabei clustered together with the isolates of Ps. cruenta on Vigna and Phaseolus form Benin (see Suppl. material 4). However, morphologically, the present species is clearly distinct from specimens of Ps. cruenta by having darker and shorter conidiophores and above all, shorter conidia [(20.5-)24-82(-84.5) μm] (Table 7 ). It is not possible to distinguish Ps. tabei from other numerous Pseudocercospora spp. by the phylogenetic analyses based on ITS sequences.

Based on a MegaBLAST search in the NCBI GenBank nucleotide database using the tef1 sequence, the closest matches were Ps. cruenta on Phaseolus vulgaris ( Fabaceae ) from Taiwan (GenBank GU384405; Identities 283 / 312, i.e., 90%), Pseudocercospora sp. A on P. vulgaris ( Fabaceae ) from Iran MB-2015(GenBank KM452885; Identities 263 / 292, i.e., 90%) and Ps. madagascariensis on Eucalyptus camaldulensis ( Myrtaceae ) from Madagascar (GenBank KF253265; Identities 276 / 314, i.e., 88%).

Figures

Figure 1. The Bayesian phylogenetic tree inferred from DNA sequence data from the multigene alignment (SSU rDNA, LSU rDNA, ITS and tef 1) of cercosporoid species. Nodes receiving Bayesian PP ≥ 0.94 or MLBS ≥ 70 % are considered as strongly supported and are indicated by thickened branches. Names of newly described species are written in bold and red. Species newly reported for Benin are indicated by green letters. Names of host plants are written with blue letters.

Figure 14. Leaf spot symptoms associated with cercosporoid fungi A, B Nothopassalora personata on Arachis hypogaea (YMM 49 A) B close-up of lesions with caespituli C Passalora arachidicola on Arachis hypogaea (YMM 49 B) D Pseudocercospora bradburyae on Centrosema pubescens (YMM 275) E Pseudocercospora cruenta on Phaseolus sp. (YMM 288) F, G Pseudocercospora griseola on Phaseolus lunatus (YMM 297 A) G close-up of lesions with sporulation H Pseudocercospora sennicola on Senna occidentalis (YMM 12) I Pseudocercospora tabei on Vigna unguiculata (YMM 220). Scale bars: 15 mm (A, D, E, F, I); 100 μm (B, G); 12 mm (D, H).

Figure 21. Pseudocercospora tabei on Vigna unguiculata (YMM 220) A immersed stroma with conidiophores B solitary conidiophores arising from external hyphae C conidia. Scale bars: 15 μm (A); 12 μm (B); 10 μm (C).