First Report of Muyocopron laterale Causing Leaf Spot on Thaumatophyllum xanadu in Guangdong Province, China

Thaumatophyllum xanadu ([Croat, Mayo & J. Boos] Sakur., Calazans & Mayo) is a perennial plant in the family Araceae, widely cultivated in China for its ornamental value. In October 2024, leaf spot symptoms were observed on T. xanadu in a landscape garden in Shenzhen (22°35'55"N, 113°59'21"E), Guangdong Province, China, with a disease incidence of ∼20% among 100 surveyed plants. Typical symptoms initially appeared as brown spots on the leaves (0.1 to 0.6 mm in diameter) with a translucent center, surrounded by a yellow halo. The spots later expanded with dark brown to black margins, and the infected leaves became blighted and desiccated. Ten symptomatic plants were collected for pathogen isolation. Leaf pieces (5×5 mm²) from the margins of the lesions were surface sterilized with 1% NaClO for 1 min, followed by 70% ethanol for 30 s, and then rinsed three times with sterile water. Tissues were placed on PDA and incubated at 25°C. After three days, three fungal strains (MBSZU 25-044 to MBSZU 25-046) with similar morphology were obtained. Colonies on PDA reached 45 to 47 mm in diameter after 1 week at 25°C, appearing flat to slightly raised, white to grayish-white with a velvety appearance. Mycelia were superficial and immersed, composed of septate, branched, 1 to 2 µm wide, hyphae, smooth and thick-walled. All strains produced asexual structures after two months of incubation; however, no conidiomata were observed. Conidiogenous cells were pale brown, often ampulliform with a distinct flared collarette, smooth, and 6.8 to 9.1 × 10.2 to 14.0 µm. Conidia were aseptate, lunate, fusiform, curved, with a base obtuse to truncate, often guttulate, hyaline, smooth, and 12.8 to 29.1 × 3.9 to 7.5 µm (n = 50). Morphologically, all strains resembled Muyocopron spp. (Hernández-Restrepo et al. 2019). The ITS, LSU, SSU, and tef1-α genes were amplified using ITS4/ITS5, LROR/LR5, NS1/NS4, and EF1-983F/EF1-2218R (Rehner and Buckley 2005; Vilgalys and Hester 1990; White et al. 1990), respectively. The ITS (PX129250 to PX129252), LSU (PX129253 to PX129255), SSU (PX129258 to PX129260), and tef1-α (PX171910 to PX171912) sequences were deposited in GenBank. BLAST analysis demonstrated that the ITS, LSU, and tef1-α sequences matched M. laterale (CBS 141029) with similarities of 99.50%, 99.31%, and 99.44%, respectively. Phylogenetic analyses of the concatenated four (LSU, SSU, ITS, and tef1-α) genes confirmed all strains as M. laterale. Pathogenicity was assessed on wounded and unwounded healthy leaves using an attached leaf assay. All leaves were wiped with 0.1% NaClO and rinsed three times with sterile water. Each leaf received 15 µl of a conidial suspension (1 × 10⁶ conidia/ml) from 8-week-old cultures, while control leaves were treated with sterile distilled water. Plants were maintained at 25°C and 80% relative humidity. After seven days, both wounded and unwounded inoculated leaves developed brown lesions with yellow halos, consistent with those observed in the field, whereas control leaves remained symptom-free. The pathogen was re-isolated and confirmed by morphology and DNA sequencing, thereby fulfilling Koch's postulates. This study provides the first report of M. laterale causing leaf spot on T. xanadu and highlights a potential threat to the cultivation of this widely grown ornamental plant in China and other tropical regions, emphasizing the need for monitoring and management strategies to prevent economic and aesthetic losses.