First Report of Leaf Mold of Mugwort Caused by <i>Epicoccum sorghinum</i> in China

In China, mugwort (<i>Artemisia argyi</i>), an important traditional Chinese medicinal herb, is primarily cultivated in the southwestern and southern regions, with a total planting area exceeding 1 million acres. Leaf diseases significantly impact both the yield and quality of mugwort. In October 2023, leaf spot symptoms were observed in Shouguang, Weifang City, Shandong Province, China (37°28' N, 119°14' E). The disease incidence in an outdoor planting area (approximately 0.05 hectares) exceeded 90%. Initially, small brown to dark brown spots appeared on the leaves, often surrounded by yellow halos. As the disease progressed, the spots expanded into irregular lesions, sometimes coalescing into larger necrotic patches. For pathogen isolation, diseased leaf tissues were surface-sterilized with 75% alcohol for 30 seconds, rinsed with sterile water, and cultured on PDA medium at 25°C for 10 days. From 10 diseased samples, three fungal strains with similar colony morphology were obtained. Colonies initially appeared white but later developed orange, pink, or white protrusions at the center with gray-white margins, forming irregular shapes. Mature colonies turned reddish-brown. Microscopic examination revealed sporodochia with cushion-shaped bases scattered across the hyphae. The hyphae were short, thin, and branched, with erect or curved morphology. Pycnidia were spherical to conical, measuring 38-70.9 × 35-50.9 μm (n = 50). Conidia were unicellular, hyaline, and round to oval, with dimensions of 4.5-12.9 × 1.9 μm (n = 50). These morphological characteristics matched those of <i>Epicoccum</i> spp. Molecular identification was performed by sequencing the internal transcribed spacer (ITS) and the large subunit ribosomal RNA (NL) of the 28S rRNA gene using primers ITS1/ITS4 and NL1/NL4 (Li et al., 2023). BLASTn analysis showed that the ITS (accession no. PV335684) and NL (PV335688) sequences shared 99.80% (500/501 bp) and 99.65% (573/575 bp) identity, respectively, with <i>Epicoccum sorghinum</i> (MW513798.1 and PV33779.1) in the NCBI database. A multilocus phylogenetic analysis using MEGA 11 further confirmed that the isolates clustered with <i>E. sorghinum</i>. Pathogenicity tests were conducted by spraying mugwort leaves (5-9 leaf stage, 20 leaves per treatment) with a spore suspension (10⁵ spores/mL). Control leaves were treated with sterile distilled water. Plants were maintained at 25°C with a 14-hour photoperiod (three replicates per treatment). Symptoms identical to those observed in the field appeared on inoculated leaves after 10 days, while controls remained asymptomatic. <i>E. sorghinum</i> was re-isolated from the diseased leaves with 100% sequence homology, fulfilling Koch's postulates. To date, <i>E. sorghinum</i> has been reported to infect over 39 plant species (Shi et al., 2025; Zhou et al., 2025; Zou et al., 2024). However, this is the first report of <i>E. sorghinum</i> causing leaf mold on mugwort. Our findings provide a theoretical foundation for developing control strategies against this emerging disease.