Cercospora aff. canescens Ellis & G.Martin, Am. Nat. 16(12): 1003 (1882).

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

Cercospora aff. canescens Ellis & G.Martin, Am. Nat. 16(12): 1003 (1882). Figs 2B, C , 4

Type.

USA (no further data available), on Phaseolus sp. ( Fabaceae ), 1882, s.n. ( “Type?” NY, n.v.) .

For synonyms see Crous and Braun (2003) or MycoBank.

Description.

Leaf spots amphigenous, subcircular to irregularly angular, 3-11.5(-13) mm diam., occasionally crossing veins, reddish brown to slightly dark brown, with dark margin. Caespituli amphigenous, greyish brown to dark brown. Mycelium internal and external. Internal hyphae often indistinct. External hyphae branched, 2.5-3.5 μm wide, septate, olivaceous brown to brown, smooth. Stromata lacking or formed by few aggregated swollen hyphal cells, immersed in the mesophyll or in substomatal cavities, dark brown. Conidiophores in small, loose fascicles of up to 8, arising from stromata, breaking through the adaxial epidermis of the leaves or penetrating through stomatal openings, sometimes solitary arising through stomatal openings or erumpent through the cuticle, erect, straight to sinuous or somewhat geniculate, rarely branched, (16.5-)21-152(-165) × (4-)4.5-5.5 μm, 1-6-septate, brown to dark brown. Conidiogenous cells terminal, monoblastic to polyblastic, brown; loci 1.5-2.5 (-3) μm wide, thickened and darkened. Conidia solitary, narrowly obclavate to subacicular, straight to curved, (34-)38-280(-330) × (3-)3.5-4(-4.5) μm, 3-12(-14)-septate, hyaline to subhyaline, smooth, apex subacute or acute, base truncate to short obconically truncate, up to 2.5 μm wide, hila thickened and darkened.

Specimens examined.

Benin. Borgou: Parakou , c. 363 m a.s.l., 9°20'29"N, 2°37'28"E, on Calopogonium sp., 21 Sep 2019, Y. Meswaet and A. Tabé, YMM07 (M-0312643, UNIPAR) . Benin. Borgou: Parakou , c. 395 m a.s.l., 9°21'27"N, 2°36'44"E, Calopogonium sp., 17 Sep 2019, Y. Meswaet and A. Tabé, YMM08 (M-0312644) . Benin. Borgou: Parakou , c. 395 m a.s.l., 9°21'27"N, 2°36'44"E, on Vigna subterranea , 16 Sep 2019, Y. Meswaet and R. Dramani, YMM01 (M-0312645, UNIPAR) .

Herbarium specimens examined for comparison.

C. canescens . On Vigna unguiculata (as V. sinensis L.): El Salvador. Sacocoyo , 3 Jul 1943, Wellman F. L. 140 (BPI 434127B). On V. unguiculata (as V. sinensis ): USA. Illinois: Gallatin County, 8 Sep 1932, G.H. Boewe B331 ( ILL 23703 Holotype of C. vignicaulis Tehon). On V. unguiculata : USA. Illinois: Pulaski, Olmstead, 17 Sep 1933, G.H. Boewe s.n. ( ILL 24809 Paratype of C. vignicaulis ). On V. unguiculata (as V. sinensis ): USA. Illinois: White, Carmi., 10 Sep 1934, G.H. Boewe B588 ( ILL 25450 Paratype of C. vignicaulis ) .

Hosts and distribution.

On many species of Fabaceae and of other families ( Crous and Braun 2003), known worldwide, from Australia, Bangladesh, Brazil, Bolivia, Brunei, Cambodia, China, Colombia, Costa Rica, Cuba, Dominican Republic, Ecuador, Fiji, Ghana, Guyana, Haiti, Hong Kong, India, Indonesia, Iran, Japan, Kenya, Korea, Malawi, Malaysia, Malawi, Mauritius, Myanmar, Nepal, New Caledonia, New Zealand, Nigeria, Pakistan, Panama, Papua New Guinea, Peru, Philippines, Puerto Rico, Russia, Senegal, Sierra Leone, Solomon Islands, Somalia, South Africa, Saint Vincent and the Grenadines, Sudan, Tadzhikistan, Taiwan, Tanzania, Thailand, Trinidad and Tobago, Togo, Uganda, USA, Uzbekistan, Vanuatu, Venezuela, Zambia, Zimbabwe ( Chupp 1954; Ellis 1976; Shin and Kim 2001; Crous and Braun 2003; Farr and Rossman 2021).

Notes.

The present Cercospora sp. on Calopogonium sp. also occurs on Vigna subterranea with different leaf spot appearances and caespituli. The lesions on Calopogonium sp. appear to be associated with a species of Pleosporales , whereas the leaf lesions on V. subterranea apparently are not associated with any other fungus and are dark reddish brown to dark brown with a dark margin, which are typical symptoms caused by Cercospora spp. The lesions on V. subterranea are larger and more abundant than those on Calopogonium sp., with abundant, dense caespituli and with dark greyish brown pigmentation (Fig. 2C ).

Cercospora canescens is the only species of Cercospora known for Calopogonium spp. ( Farr and Rossman 2021) and has been reported from West Africa (Guinea) on Calopogonium mucunoides ( Lenné 1990). Apart from having slightly narrower conidia [(3-)3.5-4(-4.5) μm versus 2.5-5.5(-6) μm in C. canescens ] as described by Chupp (1954), Hsieh and Goh (1990) and Mulder and Holliday (1975), the present specimen from Benin is morphologically identical to C. canescens . In the phylogenetic analyses, however, DNA sequences of the two specimens from Benin cluster together but separately from sequences of C. canescens available from India. In the multi-gene tree (Fig. 1 ), C. canescens is located on a branch in a clade together with sequences of Cercospora spp. YMM3SO and YMM48SO on Sorghum bicolor ( Poaceae ) from Benin. C. canescens is known to correspond to a species complex that shows diverse morphological characteristics and genetic diversity ( Joshi et al. 2006; Groenewald et al. 2013). Although C. canescens is an economically important species, no sequence data from the type or a neotype specimen are available (e.g., Groenewald et al. 2013). These are indispensable to resolve the C. canescens species complex. The specimens collected in Benin are tentatively placed into the species complex of C. canescens until DNA sequence data from the type locality (USA) and from diverse host species are available. C. aff. canescens is cited here for the first time for Benin ( Piepenbring et al. 2020).

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 2. Leaf spot symptoms associated with Cercospora spp. A Cercospora beninensis on Crotalaria macrocalyx (YMM 11) B Cercospora aff. canescens on Calopogonium sp. (YMM 07) C Cercospora aff. canescens on Vigna subterranea (YMM 01) D Cercospora fagopyri on Lablab sp. (YMM 23 A) E Cercospora parakouensis on Desmodium tortuosum (YMM 296 A) F Cercospora phaseoli-lunati on Vigna radiata (YMM 289) G Cercospora rhynchophora on Vigna unguiculata (YMM 03 B) H Cercospora tentaculifera on Vigna unguiculata (YMM 75) I Cercospora vignae-subterraneae on Vigna subterranea (YMM 293) J Cercospora zorniicola on Zornia glochidiata (YMM 299). Scale bars: 10 mm (A, C, F, G); 12 mm (B, D, E, H, J); 6 mm (I).

Figure 4. Cercospora aff. canescens on Calopogonium sp. (YMM 07) A fascicle of conidiophores protruding from a stomatal opening B solitary conidiophores C conidia. Scale bars: 15 μm (A, C); 10 μm (B).