Cercospora sp.

Nguanhom, Jeerapa, Cheewangkoon, Ratchadawan, Groenewald, Johannes Z., Braun, Uwe, To-Anun, Chaiwat & Crous, Pedro W., 2015, Taxonomy and phylogeny of Cercospora spp. from Northern Thailand, Phytotaxa 233 (1), pp. 27-48 : 44

Cercospora sp. ( Fig. 6 ).

Specimen examined: — THAILAND. Chiang Mai: on leaves of Crassocephalum crepidioides ( Asteraceae ), 29 Mar. 2013, J. Nguanhom (specimen CBS H-22293, culture CPC 23905, CPC 23906 = CBS 140168).

Leaf spots amphigenous, circular to irregular, dark brown with pale brown centre, 3−5 mm diam. Caespituli amphigenous, punctiform, brown. Stromata medium in size, substomatal or intraepidermal, brown, 27.5–37.5 μm diam. Conidiophores in moderately large fascicles, arising from stromata, through stomata or erumpent, cylindrical to strongly geniculate, brown, paler towards the apex, unbranched, rarely constricted near the apex, 50−133 × 5−6 μm. Conidiogenous cells proliferating sympodially 2−12 times, integrated, terminal, 20−75 μm long; loci conspicuous, apical or on shoulders formed by geniculation, thickened and darkened, 2–3 μm diam. Conidia solitary, acicular, shorter ones subcylindrical, hyaline, smooth, thin-walled, straight to curved, apices subacute to obtuse, base truncate, indistinctly 3−12-septate, 27.5−180 × 2−5 μm, hila thickened and darkened, 2–3 μm wide; microcyclic conidiation observed.

Culture characteristics:— Colonies spreading, flat, with sparse to moderate aerial mycelium, folded surface and even margins, reaching 45 mm after 2 wk. On MEA pale grey, with white centres, whitish at the margin; olivaceous-grey in reverse. On PDA whitish grey; reverse olivaceous-grey. On OA whitish grey (due to aerial mycelium); reverse blackish.

Notes: —The genus Crassicephalum is close to Senecio and allied genera and in subtribe Senecioninae in tribe Senecioneae . The cercosporoid fungus on Crassocephalum crepidioides is morphologically indistinguishable from Cercospora apii s. lat., by having acicular conidia with truncate bases. C. senecionis Ellis & Everh. is morphologically very close, except for somewhat wider conidiophores, 4–8 μm, and conidia, 3–6 μm ( Braun & Mel’nik 1997). C. senecionicola Davis differs in having uniformly short, non-geniculate conidiophores, 15–55 × 4–5 μm, and acicular to obclavate conidia, 2–3.5μm wide ( Chupp 1954).The Indian C. senecionis-grahamii Thirum.&Govindu ( Thirumalachar & Govindu 1962) is morphologically barely distinguishable from material on Crassocephalum crepidioides . Erechtites is another genus belonging in subtribe Senecininae and confusable with Crassocephalum . C. erechtitis G.F. Atk. is a widespread species, also known from Asia ( Hsieh & Goh 1990), and is morphologically also similar to material on Crassocephalum , being C. apii -like in morphology. Sequence data of the species on hosts belonging to the Senecioninae , which are morphologically involved in this complex, are not yet available for comparison. Furthermore, Crassocephalum crepidioides is an African species not native in Thailand. Therefore, an infection of this host by another Cercospora species, native or exotic, cannot be excluded. Hence, the present data do not allow a final conclusion and taxonomic treatment of the Cercospora sp. occurring on Crassocephalum to be made until such time as the phylogeny of related taxa has been clarified.

Figures

FIGURE 6. Cercospora sp. (CBS H-22293). A. Leaf spot; B. Close-up of leaf spot; C, D. Conidiophores and conidiogenous cells; E−H. Conidia; I = colony on MEA.—Scale bars: C−D = 40 μm; E−H = 50 μm, G applies to H.