Plectosphaerella cucumerina (Lindf.) W. Gams, in Domsch & Gams, Fungi in Agricultural Soils: 160 (1972)

MycoBank number: MB 320609; Index Fungorum number: IF 320609; Facesoffungi number: FoF 12962; Fig. 1

Neotype – CBS H-7656, CBS 137.37 (ex-neotype)

Associated with leaf spots of Bridelia sp. Sexual morph: Vegetative hyphae 1.4–3 µm wide (x=1.88, n=40), hyaline to brown, smooth-walled, septate, branched. Ascomata developing on MEA, 145–150 × 120–147 μm (x=148×130 μm, n=5), superficial or immersed in culture colonies, scattered, solitary to gregarious, subglobose to ovoid, uni- or multi-loculate. Peridium 18–32 μm (x=24.2 μm, n=10) wide, composed of 1–3 layers, inner layers comprising hyaline to dark brown, pseudoparenchymatous cells of textura angularis, outer layers composed of thick, dark brown to black, cells of textura angularis. Asci 42–58 × 6–13 μm (x=50.7 × 8.92 μm, n=10), 8-spored, unitunicate, cylindrical to obpyriform, thick-walled at apex, with J-, sub-apical ring. Ascospores 6.75–14×2–3.65 μm (x=7.46×2.85 μm, n=30), hyaline, cylindrical to clavate or fusiform, with rounded apices and bases, smooth-walled, 1-septate, guttulate, slightly constricted in the middle. Asexual morph: Conidiophores reduced to conidiogenous cells. Conidiogenous cells 6.5–10.5×4.8–6 μm (x=8.2×5.57 μm, n=5), enteroblastic, phialidic, solitary, ellipsoidal to ovoid, smooth-walled, hyaline to pale brown. Conidia only young conidia attached to conidiogenous cells observed. Appressoria not observed.

Culture characteristics – Colonies on MEA reaching approximately 70 mm diam. after 5 days at 25 °C, flat, entire margin, aerial mycelia, dense, fast-growing, pale orange with hyaline mycelium, reverse yellowish white.

Material examined – Thailand, Chiang Mai Province, Omkoi, on living leaves of Bridelia sp. (Phyllanthaceae), 16 October 2019, Gomdola D., (MFLU 22-0174, dry culture), living culture MFLUCC 22-0114.

Hosts and distribution – Foeniculum vulgare, Helianthus annuus, Cucumis sativus, Medicago sativa, Lagenaria siceraria, Brassica oleracea, Lycopersicon esculentum, Phaseolus vulgaris, Platostoma palustre, Sedum sp., Solanum lycopersicum from China; Arabidopsis thaliana, Pyrus malus from Switzerland; Bambusa sp. from Iran; Dieffenbachia maculate, Phlox sp. from New Zealand; Galium spurium, Solanum melongena, Pisum sativum from Canada; Nicotiana tabacum from Belgium; Solanum tuberosum from Pakistan; Viola odorata from Egypt; Viola tricolor from Netherlands; Asparagus officinalis, Aquilegia flabellata, Diplotaxis tenuifolia, Capsicum annuum, Cichorium endivia, Citrullus lanatus, Cucumis melo, Ocimum basilicum, Valerianella locusta, Petroselinum crispum, Solanum lycopersicum from Italy; Glycine max, Heterodera glycines, Heuchera sanguinea, Ocimum basilicum from USA (Farr and Rossman 2023).

GenBank numbers – ITS: OP678332, LSU: OP678334

Notes – Our collection (MFLU 22-0174) clusters with the strains of Plectosphaerella cucumerina including the type strain in the combined ITS, LSU, β-tubulin and tef1-α locus analyses with ML/MP/BI=98%/98%/1.00 bootstrap support. Morphologically, our collection fits to P. cucumerina by its sexual morphic characters (Carlucci et al. 2012). Therefore, we identified our collection as P. cucumerina.

There are several reports about disease of P. cucumerina that cause necrotic leaf spots on Aquilegia flabellata in Italy (Garibaldi et al. 2021), Alfalfa root rot, fennel root rot and Chinese cabbage wilt in China (Cai et al. 2021; Zhao et al. 2021; Gao et al. 2022). Here, our P. cucumerina collection associated with leaf spots of Bridelia sp. This is the first report of this species on living leaves of Bridelia sp. from Thailand and it is a new host and geographical record (Fig. 2).

Figure 1 – Plectosphaerella cucumerina (MFLU 22-0174). a Examined materials with leaf spots. b Surface view of colony on MEA. c Reverse view of colony on MEA. d Section through ascomata. e Peridium. f Conidiogenesis g–i Germinating ascospores. tubes emerging from conidium j Asci. k–o Ascospores. Scale bar. d = 50 μm e, g-o = 10 μm f = 5 μm.

Figure 2 – The best scoring RAxML tree with a final likelihood value of − 9039.925089 for the combined dataset of ITS (473 bp), LSU (793 bp), β-tubulin (317 bp) and tef1-α (455 bp) sequence data. The topology and clade stability of the combined gene analyses was compared to the single gene analyses. The tree is rooted with Musicillium theobromae (CBS 243.74 and CBS 968.72). The matrix had 515 distinct alignment patterns with 27.20% undetermined characters and gaps. Estimated base frequencies were as follows; A=0.223589, C=0.294693, G=0.277902, T=0.203817; substitution rates AC=1.565720, AG=2.080346, AT=1.939801, CG=0.818113, CT=7.028180, GT=1.0; gamma distribution shape parameter α=0.184705. Ex-type strains are in bold and newly generated sequences are in blue bold. Bootstrap support for ML equal to or greater than 50% and BI equal to or greater than 0.90 are given above the nodes