First Report of <i>Hypomontagnella monticulosa</i> Causing Brown Blight on <i>Camellia sinensis</i> in China

Brown blight of tea plant is prevalent in China, Sri Lanka, Malaysia and India, severely affecting the yield and quality (Pandey et al.2021). In November 2023, a leaf blight disease was found in Hongmin ecological tea garden, Duyun City, Guizhou Province, China (107.52°E, 26.34°N), with an estimated incidence of 50~60% in a 2,300 m² area. Initial symptoms appeared as small, light- to dark- brown necrosis on leaf tips or margins, gradually expanding into large lesions. Fifteen diseased leaves were collected, and 15 fungal isolates were obtained via single-spore isolation (Zhang et al.2025). Briefly, small symptomatic tissues were surface-sterilized with 1% NaClO and 75% ethanol, rinsed with sterile water, air-dried, and placed on potato dextrose agar (PDA) with 0.1 g/L streptomycin at 28 °C for 2-4 days. Emerging fungal colonies were transferred to a new PDA for purification. Representative isolates STYW2, STYW11 and STYW12 exhibited white and fluffy colonies and produced ovoid, hyaline, unicellular conidia (3.27 ± 0.05 μm × 2.26 ± 0.04 μm), which were consistent with the morphological characteristics of Hypomontagnella monticulosa (former name Hypoxylon monticulosum (Lambert et al.2019). Gene regions ITS, LSU, RPB2 and TUB2 of target isolates were amplified and subsequently sequenced with the primer pairs ITS1/ITS4, LROR/LR5, fRPB2-5F/fRPB2-7cR and BT2A/BT2B, respectively (Lambert et al.2019; Tang et al.2009). Sequences of STYW2 (PQ499329, PQ496762, PX098028, PV832455,), STYW11 (PX117408, PX117580, PX127340, PX250324) and STYW12 (PX117409, PX117581, PX127341, PX250325) were deposited in GenBank. Phylogenetic analysis demonstrated that sequences of isolates had 98.51% - 99.88 % similarity to H. monticulosa isolate MUCL 54604 in GenBank, and were in a well-supported clade with H. monticulosa. Thus, the isolates were identified as H. monticulosa. Pathogenicity was confirmed on 20 potted plants (one-year-old cultivar Longjing43) in two independent experiments. A mycelial plug (4 mm diameter) or 15 μl conidial suspension (1 ×106 conidia/mL) of tested fungi was inoculated onto needle-wounded leaves of tea plants. One or two leaves were inoculated per plant, and plants treated with pure PDA or water were used as controls. All plants were in a chamber at 28 °C with 85% relative humidity. The control leaves had no visible signs of infection, while all leaves inoculated with the mycelial plug or conidial suspension of target isolates exhibited disease symptoms resembling field-infected symptoms. The fungus was re-isolated from the inoculated leaves and was confirmed as H. monticulosa based on both morphological characteristics and DNA sequence alignment (ITS, LSU, RPB2 and TUB2 region). Meanwhile, the re-isolated strains reproduced the identical symptoms on the tea plant as the original fungi, fulfilling Koch’s postulates. H. monticulosa is commonly known as a promising source of bioactive compounds isolated from marine or symbionts in some plants. However, it has recently been recognized as a phytopathogen causing leaf spots (Tian et al.2023). To our knowledge, this is the first report of brown blight in tea plants caused by H. monticulosa in China, holding significant importance for its diagnosis and management in tea cultivation.