Cercospora vignae-subterraneae 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

Cercospora vignae-subterraneae Y.Meswaet, Mangelsdorff, Yorou & M.Piepenbr. sp. nov. Figs 2I , 12

Type.

Benin. Borgou: Parakou , c. 394 m a.s.l., 9°21'25"N, 2°36'45"E, on Vigna subterranea (L.) Verdc. ( Fabaceae ), 17 Sep 2019, Y. Meswaet and R. Dramani, YMM293 (Holotype: M-0312657; Isotype: UNIPAR). Ex holotype sequences. MW834446 (SSU), MW834438 (ITS), MW848618 (tef1) .

Etymology.

The epithet Cercospora vignae - Cercospora subterraneae refers to the host species, Vigna subterranea .

Diagnosis.

Cercospora vignae-subterraneae differs from all other Cercospora spp. known on Vigna spp. in causing often necrotic leaf spots with a pale to white greyish centre, mostly hypophyllous caespituli, external hyphae, flat conidiogenous loci and shorter conidia [(19-)26.5-100(-110.5) µm].

Description.

Leaf spots amphigenous, circular or subcircular to irregularly angular, 2-6.5 mm diam., often limited by veins, brown to greyish brown, later necrotic with a pale to white greyish centre, surrounded by a darker margin, the outermost ring mostly darker than the inner margins. Caespituli amphigenous, but mostly hypophyllous, greyish brown to dark brown. Mycelium internal and external. External hyphae branched, 2-3(-3.5) μm wide, septate, olivaceous brown to brown, smooth. Stromata lacking or small, immersed in the mesophyll or in substomatal cavities. Conidiophores in small to large, loose to dense fascicles or solitary, arising through stomatal openings or breaking through the epidermis, erect, subcylindrical, sinuous or somewhat geniculate, simple or rarely branched, (28-)35.5-278(-340) × (3.5-)4-5 μm, 2-6-septate, smooth, brown to dark brown with slightly paler tips. Conidiogenous cells terminal, usually monoblastic, rarely polyblastic; loci conspicuous, often flat, (1.5-)2-3 μm wide, darkened and thickened. Conidia solitary, narrowly obclavate to subacicular, straight to curved, (19-)26.5-100(-110.5) × (2.5-)3-4 μm, (2-)3-6-septate, hyaline, smooth, apex subacute or acute, base truncate to short obconically truncate, (1.5-)2-2.5(-3) µm wide, hila thickened and darkened.

Additional specimen examined.

Benin. Alibori: Gogounou, c. 333 m a.s.l., 10°50'35"N, 2°49'42"E, on Vigna subterranea Verdc., 2 Sep 2017, Y. Meswaet and A. Tabé, YMM180 (Paratypes: M-0312658; UNIPAR).

Herbarium specimens examined for comparison.

See Cercospora aff. canescens .

Host and distribution.

On Vigna subterranea ( Fabaceae ) in Benin.

Notes.

Seven species of Cercospora have previously been recorded on Vigna spp. (Table 4 ) ( Farr and Rossman 2021). However, no species of Cercospora is known to occur on Vigna subterranea ( Farr and Rossman 2021), a plant species native to West Africa and cultivated mainly in the warm tropics of sub-Saharan Africa ( Hepper 1963). Morphologically, C. vignae-subterraneae is distinct from all seven species of Cercospora mentioned above (Table 4 ). C. apii differs from C. vignae-subterraneae by paler conidiophores occasionally arising from a developed stroma of up to 50 μm diam. and above all, longer and wider conidia [25-300 × 3-6 μm versus (19-)26.5-100(-110.5) × (2.5-)3-4 μm in C. vignae-subterraneae ] that are (0-)3-25(-30)-septate ( Hsieh and Goh 1990; Crous and Braun 2003). C. canescens causes different leaf spots and caespituli, paler and shorter conidiophores [20-200 µm versus (28-)35.5-278(-340) μm in C. vignae-subterraneae ] as well as longer conidia [25-300 μm versus (19-)26.5-100(-110.5) μm of C. vignae-subterraneae ] ( Hsieh and Goh 1990). C. canscorina forms well-developed stromata as well as paler and shorter conidiophores [29.8-85 µm versus (28-)35.5-278(-340) μm in C. vignae-subterraneae ] with 1-3 septa ( Chiddarwar 1959).

C. caracallae has densely fasciculate, unbranched and shorter conidiophores [40-80 µm versus (28-)35.5-278(-340) μm in C. vignae-subterraneae ] and slightly shorter conidia [50-75 μm versus (19-)26.5-100(-110.5) μm in C. vignae-subterraneae ] ( Spegazzini 1910). C. kikuchii has unbranched and shorter conidiophores [45-200 × 3-6.5 µm versus (28-)35.5-278(-340) μm in C. vignae-subterraneae ] and larger conidia [50-375 μm versus (19-)26.5-100(-110.5) μm in C. vignae-subterraneae ] with up to 22 septa ( Hsieh and Goh 1990). C. longispora has unbranched, shorter and narrower conidiophores [5-30 × 1.5-3 µm versus (28-)35.5-278(-340) × (3.5-)4-5 μm in C. vignae-subterraneae ] with inconspicuous conidiogenous loci and somewhat longer conidia [75-170 × 2-3.5 µm versus (19-)26.5-100(-110.5) μm in C. vignae-subterraneae ] ( Chupp 1954). C. vignigena has paler, shorter and wider conidiophores [40-130 × 5-7(-10) µm versus (28-)35.5-278(-340) × (3.5-)4-5 μm in C. vignae-subterraneae ] that are 0-3-septate, and wider conidia [(2.5-)4-6(-10) μm versus (2.5-)3-4 μm of C. vignae-subterraneae ) ( Mulder and Holliday 1975).

In the multi-gene (Fig. 1 ) and in the ITS phylogeny (see Suppl. material 3), C. vignae-subterraneae forms part of a polytomy with a relatively large genetic distance (branch length) in relation to other sequences considered in the analysis. In the tef1 phylogeny (see Suppl. material 4), it is not possible to distinguish C. vignae-subterraneae from other Cercospora spp. Based on the results of our comparative study, we propose C. vignae-subterraneae as a species new to science.

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 12. Cercospora vignae-subterraneae on Vigna subterranea (YMM 293) A fascicle of conidiophores B external hypha penetrating through a stomatal opening C solitary conidiophores arising from external hyphae D conidia. Scale bars: 20 μm (A, B); 12 μm (C); 10 μm (D).