| Summary: | <i>Penicillium italicum</i> causes blue mold disease and leads to huge economic losses in citrus production. As a natural antifungal agent, clove essential oil (CEO), which is a generally recognized as safe (GRAS) substance, shows strong in vitro activity against fungal pathogens. However, few studies on CEO for controlling postharvest blue mold disease caused by <i>P. italicum</i> in citrus fruit have been reported. Our aims were to investigate the control efficacy and possible mechanisms involved of CEO against <i>P. italicum</i>. In the present study, CEO treatment inhibited the disease development of blue mold when applied at 0.05% to 0.8% (<i>v/v</i>), and with the effective concentration being obtained as 0.4% (<i>v/v</i>). Besides its direct antifungal activity, CEO treatment also spurred a rapid accumulation of H<sub>2</sub>O<sub>2</sub> compared with untreated fruits, which might contribute to enhancing an increase in the activities of defense-related enzymes, such as β-1,3-glucanase (β-Glu), chitinase (CHI), phenylalanine ammonia-lyase (PAL), peroxidase (POD), polyphenol oxidase (PPO), and lipoxygenase (LOX) in citrus fruit. Results of real time-quantitative polymerase chain reaction (RT-qPCR) showed that the gene expressions of β-Glu, CHI, PAL, POD and PPO were up-regulated in CEO-treated fruits. At the same time, CEO treatment led to down-regulated expression of the LOX gene in citrus fruit. Clove essential oil effectively control the disease incidence of blue mold decay in citrus fruit by motivating the host-defense responses, suppressing the malondialdehyde (MDA) accumulation while enhancing the activities and gene expressions of defense-related enzymes. Our study provides an alternative preservative applying CEO to reduce postharvest fungal decay in citrus fruit.
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