Inhibitory effects of plant essential oils on pathogens in postharvest pitaya fruit

【Objective】To identify the main pathogens causing postharvest decay of pitaya fruit in Guangxi，and to evaluate the inhibitory effects of essential oils on these pathogens，which could provide technical support for the postharvest preservation of pitaya fruit.【Method】Using red pitaya （Hylocereus undatus cv. Jindu No. 1） as the experimental material，the main pathogenic species causing fruit rot were identified by combining morphological observation with ITS sequence analysis. In vitro antibacterial assays were conducted to evaluate the inhibitory effects of six plant essential oils （Syzygium aromaticum，Melaleuca alternifolia，Cinnamomum cassia，Mentha haplocalyx，Cymbopogon nardus，Thymus mongolicus） at a concentration of 1.0 mL/L. The three plant essential oils with the strongest inhibitory efficacy were further investigated using concentration screening and plant essential oil fumigation treatment to clarify their effects on pathogen growth and fruit rot.【Result】Six fungal strains were isolated from rotted pitaya tissues. Pathogenicity assays confirmed that two strains were capable of causing fruit rot of postharvest pitaya. Based on molecular identification and phylogenetic tree analysis，these strains were identified as Gilbertella persicaria and Fusarium incarnatum. Under the concentration of 1.0 mL/L，antifungal screening assays using six plant essential oils for their inhibitory effects on Gilbertella persicaria and Fusarium incarnatum showed that Syzygium aromaticum essential oil exhibited the strongest inhibitory effect （inhibition rate was 100.00%），while Melaleuca alternifolia and Cinnamomum cassia essential oils also exhibited strong efficacy （inhibition rates > 94.00%）. Further concentration screening tests revealed that the minimum inhibitory concentration （MIC） of Syzygium aromaticum essential oil was 1.0 mL/L，while the MIC of Melaleuca alternifolia and Cinnamomum cassia essential oil were both 1.2 mL/L. Furthermore，in a fumigation treatment with Melaleuca alternifolia，Cinnamomum cassia，and Syzygium aromaticum essential oils significantly reduced the rot rate of pitaya fruits inoculated with pathogens. Syzygium aromaticum essential oil treatment exhibited the strongest efficacy，resulting in a decay rate of less than 10.00% after 25 d of low-temperature storage.【Conclusion】Gilbertella persicaria and Fusarium incarnatum are identified as the main pathogenic fungi causing pitaya fruit rot. Syzygium aromaticum，Melaleuca alternifolia，and Cinnamomum cassia essential oils are found to effectively inhibit the growth of both pathogens and effectively reduce the incidence of fruit rot. Among these，Syzygium aromaticum essential oil demonstrate the best efficacy in suppressing fruit rot. Melaleuca alternifolia，Cinnamomum cassia，and Syzygium aromaticum essential oils demonstrate considerable potential for application in the controlling of rot in postharvest pitaya fruit.