First Report of Epicoccum sorghinum Causing Leaf Spot on Cassava in China

Cassava (Manihot esculenta Crantz) is an economically important crop in tropical China. In July 2025, symptoms of leaf spot were observed on the Cassava cv. SC9 in Wenchang, Hainan (19°32′16″N, 110°45′41″E). Early symptoms appeared as brown lesions, which later developed into larger chlorotic spots with aging of leaves. The disease was recorded in a 0.5-acre planting, with approximately 10% of plants showing symptoms across ten sampled individuals. Small pieces (5 x 5 mm) of three diseased spots were excised, and then surface sterilized before plating and incubating on potato dextrose agar (PDA) at 28°C. Once pure cultures were obtained from all diseased spots, they were incubated on PDA at 28°C. Three isolates were isolated from the diseased tissues, which showed cottony aerial mycelia with light pink concentric rings that appeared on the reverse side of the colony after 3 days. Conidia were unicellular, hyaline, oval, and measured 5.8 to 12.5 × 1.6 to 3.7 μm (n = 30). Chlamydospores were observed, either unicellular or multicellular. These morphological characteristics were consistent with descriptions of the genus Epicoccum (Khoo et al. 2023). Molecular identification using primers ITS1/ITS4 (White et al. 1990), Bt2a/Bt2b (Glass and Donaldson 1995) and RPB2-6F/RPB2-7R (Liu et al. 1999) was performed to amplify the internal transcribed spacer (ITS), β-tubulin (TUB), and RNA polymerase II (RPB2) regions of a representative isolate WC-02. Sequences of isolate WC-02 were deposited in GenBank as PZ185680 (ITS), PZ200895(TUB) and PZ200894(RPB2). They were 100% identity to the ITS sequence of Epicoccum sorghinum strain CN136A8 (OP596119.1) (481/481 bp), 100% identity to the TUB sequence of Epicoccum sorghinum strain WY01 (PQ201634.1) (293/293 bp), and 99% identity to the RPB2 sequence of Epicoccum sorghinum strain ws-30 (MZ968834.1) (700/705 bp) from NCBI database. A neighbor-joining phylogenetic analysis based on the concatenated ITS, TUB and RPB2 sequences, constructed using MEGA 7.0, placed WC-02 in a clade with Epicoccum sorghinum. Thus, the fungus was identified as Epicoccum sorghinum based on both morphological and molecular data. Pathogenicity tests were performed on 4-month-old tissue culture seedlings leaves of cassava cv. SC9. Superficial wounds were made on healthy leaves with a sterilized toothpick and inoculated with 5-mm mycelial plugs from a 7-day-old WC-02 culture. Control leaves received sterile PDA plugs. Three leaves per plant and five plants per treatment were used, with all plants maintained in a controlled chamber (25±2°C, 90% relative humidity, 12-h photoperiod). Within 7 days, inoculated leaves developed symptoms identical to those observed in the field, whereas control leaves remained asymptomatic. The fungus was successfully re-isolated from symptomatic tissues, and its pathogenicity was confirmed by satisfying Koch’s postulates. Control plants remained symptom-free and pathogen-negative throughout the experiments, which were conducted twice with consistent results. Based on morphological and sequence analyses, the isolate was identified as Epicoccum sorghinum. While Epicoccum sorghinum has been reported to cause leaf spot on Platostoma palustre (Khoo et al. 2023), this is the first report of it infecting cassava in China. This finding is crucial for developing diagnostic methods and informing future disease management strategies.