Cercospora rhynchophora 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 rhynchophora Y.Meswaet, Mangelsdorff, Yorou & M.Piepenbr. sp. nov. Figs 2G , 9

Type.

Benin. Borgou: Parakou , c. 385 m a.s.l., 9°20'34"N, 2°36'39"E, on Vigna unguiculata (L.) Walp. ( Fabaceae ), 14 Sep 2019, Y. Meswaet and R. Dramani, YMM03B (Holotype: M-0312652; Isotype: UNIPAR). Ex holotype sequences. MW834447 (SSU), MW834431 (LSU), MW834443 (ITS), MW848619 (tef1) .

Etymology.

The epithet Cercospora rhynchophora refers to the beak- or hook-like tips of the conidiophores, a characteristic of this species.

Diagnosis.

Cercospora rhynchophora differs from other Cercospora spp. known on Vigna spp. by causing distinct leaf spots, often well-developed stromata and up to 4 times geniculate conidiophores with often polyblastic conidiogenous cells with irregular, often beak-shaped tips.

Description.

Leaf spots amphigenous, small to fairly large, subcircular to irregularly angular, (3-)4.5-12.5 mm diam. or confluent and larger, dark brown to reddish brown, mostly with an indefinite margin, or whitish grey to greyish brown, with a narrow to wide dark brown margin on the adaxial surface, occasionally confined by veins. Caespituli amphigenous, scattered to dense, dark brown. Mycelium mainly internal, but some external hyphae also present. External hyphae septate, brown, 2-3.5 μm wide, smooth. Stromata often well-developed, up to 50 μm diam., in substomatal chambers or in the mesophyll, brown to dark brown. Conidiophores in loose to moderately dense fascicles formed by 3-20 conidiophores, arising from internal hyphae or stromata breaking through the adaxial epidermis of the leaves, or penetrating through stomatal openings, or solitary, erect, straight to 1-4 times geniculate or subcylindrical, sometimes branched, mostly attenuated towards the tips that are often irregularly shaped or conical, (12.5-)26-160(-200) × (3.5-)4-5(-5.5) μm, 0-7(-9)-septate, brown to dark brown. Conidiogenous cells terminal or rarely intercalary, proliferating sympodially, mostly polyblastic, frequently distinctly subdenticulate, sometimes with bent tips looking like a beak or a hook; loci (1.5-)2-2.5(-3) μm wide, thickened and darkened. Conidia solitary, acicular to narrowly obclavate, straight to curved, (28-)40-265(-280) × (3-)3.5-4.5(-5) μm, 1-9-septate, hyaline, smooth, tip acute, base truncate to obconically truncate, sometimes long obconically truncate, 2-2.5(-3.5) μm wide, hila thickened and darkened.

Additional specimen examined.

Benin. Borgou: Parakou, c. 395 m a.s.l., 9°21'27"N, 2°36'44"E, on Vigna unguiculata , 17 Sep 2019, Y. Meswaet and R. Dramani, YMM03C (Paratypes: M-0312653; UNIPAR).

Herbarium specimens examined for comparison.

See Cercospora aff. canescens .

Host and distribution.

On Vigna unguiculata ( Fabaceae ) in Benin.

Notes.

The infection of leaves of Vigna unguiculata by Cercospora rhynchophora was severe and caused dark brown to reddish brown large patches (Fig. 2G ). This infection was frequently associated with an infection by Pseudocercospora cruenta (Sacc.) Deighton. Seven species of Cercospora have previously been recorded on Vigna spp. (Table 4 ). Among these, C. apii , C. canescens , C. kikuchii and C. vignigena have to date been reported as agents of leaf spot diseases on V. unguiculata . Morphologically, C. rhynchophora differs from these species by a specific combination of characteristics (Table 4 ). C. apii has often small or no stromata, forms non-geniculate, densely fasciculate and longer conidiophores (20-300 μm) that are uniform in colour and width and carry monoblastic conidiogenous cells ( Chupp 1954; Hsieh and Goh 1990) versus developed stromata, shorter conidiophores [(12.5-)26-160(-200) μm] that are irregularly shaped with polyblastic conidiogenous cells presenting beak-shaped tips in C. rhynchophora . Additionally, C. apii has pale to olivaceous brown conidiophores ( Hsieh and Goh 1990) versus the dark brown ones of Cercospora rhynchophora .

C. canescens causes different leaf spots and caespituli, develops small or no stromata and paler conidiophores that are uniform in colour with often monoblastic, mostly uniform conidiogenous cells ( Chupp 1954; Hsieh and Goh 1990) versus irregularly shaped conidiophores with polyblastic, beaked conidiogenous cells in C. rhynchophora . The distinctness is also confirmed by molecular data. C. canscorina forms shorter conidiophores [29.8-85.0 µm versus (12.5-)26-160(-200) μm in C. rhynchophora ] and conidia [31.2-89.9 × 3-3.4 μm versus (28-)40-265(-280) μm in C. rhynchophora ] with pale brown and 1-3-septate conidiophores ( Chiddarwar 1959). C. caracallae has densely fasciculate, unbranched, shorter and wider conidiophores [40-80 × 5-6 µm versus (12.5-)26-160(-200) μm in C. rhynchophora ] and shorter conidia [50-75 μm versus (28-)40-265(-280) μm of C. rhynchophora ] with 3-5 septa ( Spegazzini 1910). C. kikuchii has unbranched conidiophores and longer conidia [50-375 μm versus (28-)40-265(-280) μm in C. rhynchophora ] that are 0-22-septate ( Hsieh and Goh 1990). C. longispora has shorter and narrower conidiophores [5-30 × 1.5-3 µm versus (12.5-)26-160(-200) × (3.5-)4-5(-5.5) μm in C. rhynchophora ] and shorter conidia (75-170 µm versus (28-)40-265(-280) in C. rhynchophora ] ( Chupp 1954). C. vignigena produces pale brown and wider conidiophores [5-7(-10) µm versus (3.5-)4-5(-5.5) μm in C. rhynchophora ] that are 0-3-septate and shorter as well as wider conidia [(35-)45-70(-150) × (2.5-)4-6(-10) μm versus (28-)40-265(-280) × (3-)3.5-4.5(-5) μm of C. rhynchophora ] ( Groenewald et al. 2013).

In the multi-gene (Fig. 1 ) and the ITS tree (see Suppl. material 3), C. rhynchophora forms part of a polytomy with a relatively large genetic distance (branch length) in relation to other sequences considered in the analysis. According to a MegaBLAST search using the tef1 sequence, the closest matches in NCBI’s GenBank nucleotide database were Cercospora beticola Sacc. on Tetragonia tetragonoides (Pall.) Kuntze ( Aizoaceae ) from Brazil (GenBank MN517124; Identities 272 / 279, i.e., 97%), Cercospora kikuchii on Platostoma palustre (Blume) A.J. Paton ( Lamiaceae ) from Taiwan (GenBank LC488192; Identities 272 / 279, i.e., 97%) and Cercospora sp. RF5 on Brunfelsia hopeana (Hook.) Benth. ( Solanaceae ) from Thailand (GenBank AB863025; Identities 272 / 279, i.e., 97%).

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 9. Cercospora rhynchophora on Vigna unguiculata (YMM 03 B) A fascicle of conidiophores growing out from a developed stroma embedded in the mesophyll B conidiophore penetrating through a stomatal opening C solitary conidiophores arising from external hyphae D conidia. Scale bars: 20 μm (A, B); 15 μm (C, D).