Pseudocercospora sennicola 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 sennicola Y.Meswaet, Mangelsdorff, Yorou & M.Piepenbr. sp. nov. Figs 14H , 20

Type.

Benin. Atlantique: Cotonou, University of Abomey-Calavi , c. 9 m a.s.l., 6°24'45"N, 2°20'41"E on Senna occidentalis (L.) Link ( Fabaceae ), 23 Sep 2019, Y. Meswaet and A. Tabé, YMM12 (Holotype: M-0312676; Isotype: UNIPAR). Ex holotype sequences. MW834444 (SSU), MW834432 (LSU), MW850550 (ITS) .

Etymology.

The epithet Pseudocercospora sennicola refers to the host genus Senna and - cola (lat. colere = to dwell).

Diagnosis.

Pseudocercospora sennicola differs from other Pseudocercospora spp. known on Senna spp. by causing often inconspicuous spots and the combination of branched and relatively long conidiophores [16.5-)20.5-92(-98) µm] and relatively short and wide conidia [(16-)22-54.5(-65) × 3-4.5(-5) μm] that are often constricted at the septa (Table 6 ).

Description.

Leaf spots lacking or indistinct to pale brown discolorations, amphigenous, subcircular to irregularly angular, (2-)4.5-10.5 mm diam., occasionally surrounded by a darker margin. Caespituli amphigenous, loose, olivaceous brown. Mycelium internal and external. External hyphae branched, 2.5-3.5 μm wide, septate, olivaceous brown to brown, smooth. Stromata lacking to slightly developed, in substomatal cavities or partly embedded in the mesophyll, 10-20 μm diam., brown to dark brown. Conidiophores in small, loose fascicles of up to approx. 10 conidiophores, arising from internal hyphae or hyphal aggregations, breaking through the adaxial epidermis of the leaves or penetrating through stomatal openings, or solitary, arising from external hyphae, erect to decumbent, flexuous, simple or occasionally branched, subcylindrical to somewhat clavate, geniculate-sinuous, slightly narrower towards the tips, (16.5-)20.5-92(-98) × (3-)3.5-4.5 μm, 2-6(-8)-septate, smooth, olivaceous brown to slightly dark brown, paler towards the tips. Conidiogenous cells terminal or lateral, medium brown, smooth, proliferating sympodially, with slightly tapering to flat-tipped apical loci; loci 1.5-2.5 μm wide, not thickened and not darkened. Conidia solitary, narrowly obclavate to subacicular, straight to curved, (16-)22-54.5(-65) × 3-4.5(-5) μm, 2-6-septate, often constricted at the septa, olivaceous brown, smooth, apex subacute, base truncate to obconically truncate, 1.5-2.5 μm wide, hila not thickened and not darkened.

Additional specimen examined.

Benin. Atlantique: Cotonou, University of Abomey-Calavi, c. 9 m a.s.l., 6°24'45"N, 2°20'41"E, on Senna occidentalis , 26 Sep 2019, Y. Meswaet and A. Tabé, YMM12B (Paratypes: M-0312677; UNIPAR).

Herbarium specimens examined for comparison.

On Senna occidentalis (as Cassia occidentalis L.): USA. South Carolina: Aiken, 1876, Ravenel H. W. s.n. (BPI 439584, Holotype of Cladosporium personatum var. cassiae Thüm.) .

Host and distribution.

On Senna occidentalis ( Fabaceae ) in Benin.

Notes.

Currently, eleven Pseudocercospora species are known on Senna spp. ( Fabaceae ), namely Ps. angustata (Chupp & Solheim) Deighton on Senna hirsuta (L.) H.S. Irwin & Barneby, Ps. cassiae-alatae (J.M. Yen & Lim) J.M. Yen on S. alata (L.) Roxb., Ps. cassiae-fistulae Goh & W.H. Hsieh on Cassia fistula L. and S. rizzinii H.S. Irwin & Barneby, Ps. cassiae-occidentalis (J.M. Yen) J.M. Yen on S. occidentalis , Ps. cassiae-siameae (Chidd.) Deighton on S. siamea (Lam.) H.S. Irwin & Barneby, Ps. nigricans (Cooke) Deighton on Senna spp., Ps. sennae-multijugae on S. multijuga (Rich.) H.S. Irwin & Barneby, Ps. sennae-rugosae A. Hern. Gut., Z.M. Chaves & Dianese on S. rugosa (G. Don) H.S. Irwin & Barneby, Ps. singaporensis (J.M. Yen) J.M. Yen on S. occidentalis (L.) Link, Ps. taichungensis Goh & W.H. Hsieh on S. atomaria (L.) H.S. Irwin & Barneby ( Hernández-Gutiérrez et al. 2015; Farr and Rossman 2021). Among these eleven species of Pseudocercospora , only Ps. nigricans and Ps. singaporensis have some similarity with the species described here (Table 6 ). Ps. sennicola , however, differs from Ps. nigricans in causing often indistinct leaf spots, shorter conidiophores [(16.5-)20.5-92(-98) μm versus 15-125 µm in Ps. nigricans ] with 6(-8) septa and shorter conidia [(16-)22-54.5(-65) versus 20-80 μm in Ps. nigricans ] ( Hsieh and Goh 1990). Ps. sennicola differs from Ps. singaporensis by causing often indistinct leaf spots, slightly developed stromata, longer conidiophores [(16.5-)20.5-92(-98) μm versus 31-77 µm in Ps. singaporensis ] and shorter conidia [(16-)22-54.5(-65) versus 30-67 μm in Ps. singaporensis ] ( Yen and Lim 1980). Moreover, the specimen from Benin has conidia with more septa (2-6 versus strictly 3-septate in Ps. singaporensis ) and conidial walls constricted at the septa.

In the multi-gene tree (Fig. 1 ), Ps. sennicola is located in a polytomy at the end of a long branch reflecting a long genetic distance to other species included in the analysis. Morphologically, Ps. sennicola is distinct from all Pseudocercospora species known on species of Fabaceae from Benin by longer conidiophores [(16.5-)20.5-92(-98) μm] and smaller conidia [(16-)22-54.5(-65) μm)].

Based on a MegaBLAST search using the ITS sequence data, the closest matches in NCBI’s GenBank nucleotide database were Pseudocercospora fuligena on Lycopersicon sp. ( Solanaceae ) from Thailand (GenBank GU214675; Identities 674/687, i.e., 98%), Pseudocercospora chengtuensis on Lycium chinense ( Solanaceae ) from South Korea (GenBank GU214672; Identities 674/687, i.e., 98%) and Pseudocercospora atromarginalis on Solanum nigrum L. ( Solanaceae ) from South Korea (GenBank GU214671; Identities 673/687, i.e., 97%). Based on the result of our comparative study, we consider the present Pseudocercospora species on Senna occidentalis from Benin to represent a distinct species, which is described here. However, as sequence data are only available for Ps. sennae-multijugae , more molecular sequence data are needed to clarify the species delimitations among these twelve Ps. species on Senna spp.

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 20. Pseudocercospora sennicola on Senna occidentalis (YMM 12) A fascicle of conidiophores growing out of a small stroma embedded in the epidermis B solitary conidiophores arising from external hyphae C conidia. Scale bars: 15 μm (A); 10 μm (B, C).