Fusarium languescens
Fusarium languescens L. Lombard & Crous, Persoonia 41: 28 (2018)
Index Fungorum number: IF 826843 Facesoffungi number:
Associated with tuber rot of lesser yam (Dioscorea esculenta). Sexual morph not observed. Conidiophores on aerial mycelium unbranched or slightly branched, comprise terminal or intercalar monophialides, frequently reduced to single phialides. Aerial phialides subulate to subcylindrical, smooth, and thin-walled, 6.5–18 × 2–3.8 µm (Mean = 15 × 2.5 µm, n = 15), with unnoticeable or absent periclinal thickening. Microconidia ellipsoidal to falcate, hyaline, smooth, thin-walled, 0-septate, 3.6–9 × 2–3.4 µm (Mean = 6 × 2.5 µm, n = 30), formed in a small false head on the tips of the phialides on SNA. Sporodochia light orange on carnation leaves. Conidiophores in sporodochia verticillately branched, comprising a short, smooth, and thin-walled stipe, carrying apical whorls of 2–3 monophialides or scarcely single lateral monophialides. Sporodochial phialides subulate to subcylindrical, smooth, and thin-walled. Sporodochial conidia falcate, curved dorsiventrally, with almost parallel sides tapering a little towards both ends, with a blunt papillate and curved apical cell. Basal cells are blunt to foot-like, 1–5 septate, hyaline, smooth, and thin-walled; 1-septate conidia 18–23 × 3–4 µm (mean = 20 × 3 µm, n = 20); 2-septate conidia 15–22 × 3–4 µm (mean = 18 × 3 µm, n = 20); 3-septate conidia 25–37 × 3–5 µm (mean = 31 × 4 µm, n = 20); 5-septate conidia 33–41 × 4–5 µm (mean = 35 × 5 µm, n = 20). Chlamydospores globose to subglobose, formed terminally, 7–8 µm in diameter.
Culture characteristics: Colonies on PDA reach 80–85 mm in diameter after 7 days of growth at 25 °C in the dark, white to pale vinaceous, floccose with plentiful aerial mycelium. The margins of colonies are irregular, serrate, or filiform. The reverse is pale rosy.
Material examined: Thailand Chiang Rai Province, Mueang Chiang Rai District, Doi Hang, on lesser yam (Dioscorea esculenta), February 2023, Maryam Fallahi, dried culture MF67-4 (MFLU 24-0252), living culture, MFLUCC 24-0249.
Notes: Based on the phylogenetic tree generated for Fusarium oxysporum species complex (FOSC), strain MFLUCC 24-0249 clustered with F. languescens (CBS 645.78, ex-type) with 97% ML, 96% IQ bootstrap support, and 1.0 BYPP. The base pair differences between F. languescens strains MFLUCC 24-0249 and ex-type CBS 645.78 revealed a 0.33% (2/601 bp) difference in tef1, a 0.25% (2/795 bp) difference in rpb1, and no difference in rpb2. Phylogenetic analysis by Lombard et al. (2019) revealed that F. languescens establishes a subclade as highly supported, which mostly includes strains related to tomato wilt. Fusarium languescens shows morphological overlap with several species. Hence, phylogenetic inference is required to identify them correctly. Recently, several putative species, six belonging to FOSC (F. aff. cugenangense, F. aff. curvatum, F. aff. gossypinum, F. aff. nirenbergiae, F. aff. odoratissimum, and Fusarium aff. sp.), F. aff. asiaticum, F. aff. commune, F. aff. fujikuroi, F. aff. solani, and F. aff. Verticillioides, were reported from Chinese yam (Dioscorea polystachya Thunb.) in China (Dongzhen et al. 2020). Dongzhen et al. (2020) stated these species are potentially new taxa, and they used “species affinis” or “aff. sp.” for short to the tentative nature of their species identifications. This is the first report of F. languescens on lesser yam in the world and Thailand.
Figure 1. Phylogenetic tree of the Fusarium oxysporum species complex generated by maximum likelihood of combined tef1, rpb1, and rpb2 sequence data. The ultrafast maximum likelihood (ML) and IQ bootstrap support values ≥ 50% as well as Bayesian posterior probabilities ≥ 0.95 (BYPP) are shown, respectively, near the nodes. The ex-type strains are marked with an asterisk. The tree is rooted in Fusarium proliferatum (CBS 480 96).
Figure 2. Fusarium languescens (MFLUCC 24-0249) a tuber rot in lesser yam b front, and c back views of the colony after seven days of growth on PDA at 25 °C d sporodochium e sporodochial conidiophore and phialides f, g sporodochial conidia h chlamydospore i–k aerial conidiophores, conidiogenous cells, and conidia. Scale bars: 20 μm (e–g); 10 μm (h, i); 5 μm (j, k).
- Fallahi M, Armand A, AI-Otibi F, Hyde KD. Pathogenic fungi (Sordariomycetes) associated with annual and perennial crops in Northern Thailand. MycoKeys 117, 191–265.
https://doi.org/10.3897/mycokeys.117.137112
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