Tea (Camellia sinensis), widely cultivated for non-alcoholic beverage production, is susceptible to various fungal diseases (Pandey et al. 2021). In June 2021, widespread light-brown lesions were observed on tea plants across 5,000 m2 of cultivated fields in Leishan County (26°23′12.8″N, 108°4′19.2″E), Guizhou Province. The incidence rate of the disease in the sampling areas was about 35%. In the early stages, small, round, or irregular spots appeared on the leaves. As the disease progressed, the lesions gradually expanded, ultimately resulting in leaf drop. To identify the fungal pathogens responsible for these symptoms, 15 symptomatic leaf samples were randomly collected. After washing the samples with sterile distilled water, infected tissue (5 × 5 mm) was disinfected with 75% alcohol for 30 seconds, then soaked in 1% sodium hypochlorite solution for 60 seconds, followed by rinsing with sterile water three times. After that, surface moisture was blotted dry with sterile filter paper, and finally, the samples were transferred to potato dextrose agar (PDA) medium, they were cultured in the dark in a constant temperature incubator at 28 ℃. After the colonies grew, mycelial blocks were picked from the edge of the colonies and transferred to new PDA medium for purification to obtain pure cultures. A total of 12 fungal colonies were transferred to PDA medium for further purification and morphological observation. Three isolates exhibiting identical colony morphology and color were obtained, and isolate 3a-G-2 was selected as the representative for further study. Conidia are numerous, clustered, ovoid, colorless, and measure 2.6–4.1 µm by 1.3–1.9 µm (average 3.35 × 1.6 μm, n = 42). These characteristics were similar to those reported for Irpex lacteus (Sun et al. 2025). The internal transcribed spacer (ITS) and large subunit (LSU) regions were amplified and sequenced for three isolates (3a-G-2, 3a-P-3, and 4a-B-1) using the primer pairs ITS1/ITS4 and NL1/NL4 (Vilgalys and Hester 1990, White et al. 1990). The sequences have been deposited in GenBank under the following accession numbers: OP415495, OP415496, and OP415497 for ITS; and OP415539, OP415540, and OP415541 for LSU. BLAST searches of the sequences revealed 99.25% (652/672 nt) and 100% (613/917 nt) homology with those of I. lacteus CBS:431.48 from GenBank (MH856423.1 and MH867969.1), respectively. Phylogenetic analysis using maximum-likelihood and Bayesian methods placed the isolate 3a-G-2 in a well-supported cluster with I. lacteus (Ronquist et al. 2012, Stamatakis 2014). To confirm Koch’s postulates, healthy tea leaves were surface-sterilized with 75% ethanol and then sprayed with a spore suspension at 1 × 106 CFU/mL. A sterile water treatment served as the control. The experiment was repeated three times, with each including three plants from the experimental group and three from the control group. Five days after inoculation, the observed disease symptoms resembled those seen in the field, while the control plants remained healthy. The fungus was reisolated from the symptomatic tissues and identified as I. lacteus. To our knowledge, this is the first report of I. lacteus causing leaf spot on tea in China. Our findings provide a theoretical basis and technical support for the effective prevention and control of tea leaf spot disease.
Lei et al. (Sun,) studied this question.