Objective This study was conducted to investigate the pathogenic characteristics of Pestalotiopsis trachicarpicola (abbreviated as P. trach.), the causal agent of tea gray blight, screen high-efficiency and low-toxicity alternative fungicides against this pathogen, and clarify the preliminary mechanism of action of core fungicides. The findings are expected to provide a scientific basis for seasonal precision application and fungicide rotation in tea plantations for the management of this disease.

Method The mycelial growth rate method was employed to determine the inhibitory activity and half-maximal effective concentration (EC₅₀) of 18 fungicides against P. trach. at a concentration of 100 μg/mL. At a concentration of 10 μg/mL, the protective and curative activities of prochloraz, pyraclostrobin and thiophanate-methyl against tea gray blight were evaluated. The membrane damage effect of prochloraz on P. trach. was preliminarily explored using the extracellular conductivity measurement method and propidium iodide (PI) staining assay.

Result Significant differences in inhibitory activity against P. trach. were observed among the 18 tested fungicides. Among them, prochloraz, iprodione and pyraclostrobin exhibited inhibition rates exceeding 90%, showing strong antifungal potential. The EC₅₀ values of prochloraz, pyraclostrobin and thiophanate-methyl were 0.17, 0.18 and 1.22 μg/mL, respectively, which were superior to that of the reference fungicide carboxin (12.26 μg/mL).In vivo inoculation tests demonstrated that the protective activity (55.65%) and curative activity (58.45%) of prochloraz were 29.56 and 39.98 percentage points higher than those of the positive control carboxin (26.09% and 18.47%), respectively, indicating the best comprehensive control efficacy. Pyraclostrobin showed strong protective activity while thiophanate-methyl exhibited stable curative activity, and the three fungicides had complementary functions.The study on membrane permeability revealed that after treatment of P. trach. with 4 μg/mL prochloraz for 8 h, the absolute extracellular conductivity (7.85 μS/cm) and relative conductivity (71.04%) of the pathogen were significantly higher than those of the blank control CK₂ (4.81 μS/cm and 44.17%).This indicated that prochloraz could destroy the integrity of the pathogen, s cell membrane, leading to the leakage of intracellular electrolytes. Fluorescence microscopy observations showed that the degree of cell membrane damage of P. trach. caused by prochloraz increased with the extension of treatment time, further confirming its destructive effect on the cell membrane.

Conclusion Prochloraz, pyraclostrobin and thiophanate-methyl exhibit excellent comprehensive control efficacy, strong protective activity and stable curative activity respectively, with the advantage of low application dosage. They provide a core fungicide rotation combination for constructing a control strategy based on the seasonal occurrence regularity of the disease. Among them, prochloraz exerts its antibacterial effect by damaging the cell membrane integrity of P. trach., and can be used as a core alternative fungicide for the control of tea gray blight.