First Report of Epicoccum poaceicola Causing Leaf Spot on Phyllostachys viridis in China

Abstract

<jats:p> Phyllostachys viridis (Poaceae) is a bamboo species broadly distributed in Asia. It is not only used as raw material in papermaking and food processing, but also used as an evergreen ornamental in the parks and landscapes of China. In February 2019, a leaf spot disease was found on P. viridis in Jurong, Zhenjiang, Jiangsu of China. The incidence rate of this disease was ca. 53%. The disease primarily appeared as orange chlorotic spots on the leaves. The spots enlarged and coalesced to form irregular brown necrotic lesions (Fig. S1A). Symptomatic leaves were collected, and twelve cuttings were made from the margin of the lesions of ca. 3×3 mm, surface-sterilized using 75% ethanol for 1 min, rinsed three times in sterile distilled water, and placed on 2% of potato dextrose agar (PDA) in Petri plates for 5 days at 25°C. Twenty-two fungal isolates were single-spored and stored in the Forest Pathology Laboratory at Nanjing Forestry University. Pathogenicity of all isolates was tested on leaves of P. viridis using mycelial discs. Mycelial plugs (5-mm-diameter discs) of each isolate were taken from the margins of colonies grown on PDA for 5 days and inoculated onto healthy leaves which were surface-sterilized using 75% ethanol and wounded with a sterilized needle. PDA discs without fungi were used to treat the control leaves. The inoculated whole plants were kept in a growth chamber at ca. 25°C at 85% relative humidity. The experiment was repeated twice and there were at least five replicates for each treatment. After 5 days post inoculation, the leaves inoculated with isolate PV2-9 showed necrotic lesions. No lesions were found on the plants inoculated by other fungal isolates and the control PDA plugs (Fig. S1B). The pathogen was re-isolated from the infected leaves, which shared similar morphological characteristics of colonies, aerial mycelia, and conidia with the original inoculated isolate PV2-9. Identification of the fungus was based on both morphological characteristics and molecular methods. Colonies of the isolate PV2-9 on PDA were white, floccose, round, pale grey with pale-reddish pigmentation near the center (Fig. S1C). The colonies attained 65±0.3 mm diam after 7 days at 25 oC. Abundant conidiomata were observed over the medium after 4 weeks (Fig. S1D). Conidiomata were pycnidial, solitary or gregarious, scattered, semi-immersed to erumpent, or superficial uniloculate to multi-loculate, globose to subglobose, ostiolate, 105.2-162.1× 90.3-116.2 μm (x=122.6±14.4 × 97.9±6.8 μm, n=30). Pycnidial wall was comprising 3-7 layers of dark brown to lightly pigmented, 13.4–19.7 μm thick (x =16.4 ± 1.6 μm, n=30) (Fig. S1E, F). Conidiogenous cells were phialidic, hyaline, smooth, flask-shaped to doliiform, lining the conidiomatal cavity (Fig. S1G). Conidia were ellipsoidal to cylindrical, smooth, hyaline, aseptate, 4.0–6.2 × 2.4–3.3 μm (x =4.8 ± 0.5 ×2.5 ± 0.3, n=30), with 0–3 guttules (Fig. S1H). These morphological characteristics matched the Epicoccum poaceicola described by Thambugala et al. (2017). The internal transcribed spacer (ITS) region of rDNA, 28S large subunit ribosomal RNA gene (LSR), RNA polymerase II second largest subunit gene (RPB2), and beta-tubulin gene (TUB) were amplified using the primers published in Raza et al. (2019). The ITS (MT110918), LSU (MT110921), TUB (MT119149), and RPB2 (MT119150) showed 99.3%, 99.8%, 98.1%, and 99.8% identity to the corresponding sequences of E. poaceicola ex-type MFLUCC 15-0448, respectively. Phylogenetic analysis using concatenated sequences of ITS, LSU, TUB and RPB2 also showed that PV2-9 clustered monophyletically with E. poaceicola MFLUCC 15-0448 and supported with a high bootstrap (98%) value (Fig. S2). Based on morphological and phylogenetic data, PV2-9 was identified as E. poaceicola. E. poaceicola has been collected from dead leaves of Poaceae sp. and described as a new species by Hyde et al. (2018). To our knowledge, this is the first report of E. poaceicola causing leaf spot on P. viridis in China. Further studies are needed to assess its impact on P. viridis, as well as monitor and control this disease. </jats:p>

Didymellaceae species associated with tea plant (Camellia sinensis) in China

“…Conidia produced by E. poaceicola were ellipsoidal to cylindrical and sometimes with small guttules ( Thambugala et al 2017 ). Epicoccum poaceicola can cause leaf spot in bamboo, camphor tree and eggplant ( Liu et al 2020 ; Li et al 2022 ; Aementado and Balendres 2023 ). In the present study, seven strains were isolated from healthy tea plant leaves.…”