Abstract: To identify the pathogen and its taxonomic status causing a new leaf spot disease in the Yongzhou tobacco-growing area of Hunan Province, and to screen effective control agents through laboratory toxicity assays, in this study, tobacco leaves were collected from the tobacco-growing regions of Yongzhou. The pathogen was isolated via tissue culture, single-spore isolation, and purification. Pathogenicity was confirmed through in vitro inoculation. The pathogen was identified by PCR amplification and sequencing of the ITS region, followed by phylogenetic analysis, combined with morphological characterization of colonies and spores. The indoor toxicity of nine fungicides, including 43% Fluopyram·Trifloxystrobin (SC), against the pathogen was determined using the mycelial growth rate method. Laboratory toxicity tests indicated that 43% Fluopyram‌·Trifloxystrobin (SC), 70% Thiophanate-methyl (WP), and 42.4% Pyraclostrobin·Fluopyram (SC) exhibited the strongest inhibitory effects against Corynespora. cassiicola, with EC50 values of 3.028 5 mg/L, 5.148 0 mg/L, and 8.787 9 mg/L, respectively. Moderately effective fungicides included 70% Mancozeb (WP), 75% Trifloxystrobin·Tebuconazole (WG), 32.5% Benzovindiflupyr·Azoxystrobin (SC), and 38% Pyraclostrobin·Boscalid (WG), with EC50 values of 21.844 3 mg/L, 31.841 8 mg/L, 32.080 1 mg/L, and 41.867 6 mg/L, respectively. The least effective agents were 40% Mefentrifluconazole·Pyraclostrobin (SC) and 75% Chlorothalonil (WP), with EC50 values of 192.466 9 mg/L and 1 341.062 0 mg/L, respectively. This study revealed that the new leaf spot disease on tobacco in Yongzhou was caused by C. cassiicola. C. cassiicola was identified as the causal agent of Corynespora leaf spot disease in tobacco. Strobilurin and benzimidazole fungicides showed superior inhibitory efficacy. The findings provide a scientific basis for the effective local control of tobacco Corynespora leaf spot disease.
Key words: tobacco; Corynespora leaf spot disease; Corynespora cassiicola; indoor virulence assay; fungicide
（Acta Laser Biology Sinica, 2026, 35(1): 053-061）