Novel Essential\nOil-Based Thiosemicarbazone Compounds\nas Potential Fungicides in Controlling Postharvest Diseases of Citrus\nFruit

To develop novel fungicides for controlling postharvest\nfungal\ndiseases in citrus fruits, 12 essential oil (EO)-based thiosemicarbazones\ncompounds, termed hydrazine-carbothioamide, were prepared according\nto the condensation method. <i>In vitro</i> assays showed\nthat compound 13j exhibited the strongest antifungal activity (minimum\ninhibitory concentration [MIC] = minimum fungicidal concentration\n[MFC] = 0.0125 mg/mL) against Penicillium digitatum. An <i>in vivo</i> study revealed that 5 × MFC of\ncompound 13j can effectively mitigate the green mold incidence of\ncitrus fruit inoculated with P. digitatum, as well as fruit rot during natural storage, at a level comparable\nto that of the chemical fungicide prochloraz. Throughout this process,\nfruit quality was maintained. The hemolysis assay showed that these\nthiosemicarbazone compounds have good biocompatibility and that their\nsafety is comparable to that of prochloraz. The antifungal activity\nof compound 13j was attributed to membrane damage, as confirmed using\nscanning electron microscopy (SEM), Calcofluor white (CFW) staining,\npropidium iodide (PI) staining, Fourier transform-infrared (FT-IR)\nspectroscopy, optical density (OD)<sub>260</sub>, and relative conductivity\nassays. Collectively, our results indicate that compound 13j can be\nused as an antifungal agent to control the postharvest decay of citrus\nfruits.