Abstract
Postharvest disease of peach is considered the main reason of fruit spoilage, especially under warm conditions . Pesticides are not preferable to be used in the control of such disease due to their direct harmful effect on the human health. Therefore, finding of safe, natural and effective products, such as the essential oils, is of great importance. Therefore, the aim of this study was the isolation and identification of the causal pathogens of the postharvest disease of peach fruits and application of the available and common essential oil to biocontrol the postharvest and g manage the fruit quality. The mechanism by which the essential oils could suppress the pathogens to reduce the disease severity was investigated. To achieve the goals of this study, many experiments including the in vitro and in vivo trials were conducted including, the isolation of the causal organism on synthetic media, pathogenicity test and screening of nine essential oils for their control potentiality against the fungal pathogens were carried out. Effect of storage temperature on the disease progress and biocontrol efficiency were evaluated. The mechanism(s) of action of the effective oils were explored using electron microscopy and the analysis of the oil constituents by GC-MS. The obtained results revealed that peach fruits collected for Abha, Jazan and Tahamh were subjected to the postharvest spoilage a high percentage (22.7%.). Alternaria alternata, Botrytis cinerea, Fusarium oxysporum, Geotrichum candidum, Monilinia laxa, Pencillium expansum and Rhizopus stolonifer were isolated as the main causal pathogens of the postharvest disease of peach fruit. Botrytis cinerea infected about 40% of peach fruits followed by Rhizopus stolonifer and Monilinia laxa, however, the other four fungi recorded the lowest degree of incidence. Pathogenicity test confirmed the ability of the seven fungi to cause postharvest disease of peach fruits. In vitro screening test showed that the nine tested essential oils suppressed the fungal growth, however lemon, thyme and mint were the most effective oils. Application of the three essential oils in vivo reduced the disease severity and protected the peach fruits free of infection. It also succeeded to control the disease under different temperatures (20, 30°C and room temperature), however, it was more effective in the room temperature test. Under cold storage (4 °C), application of the essential oils increased the shelf-life and storage of peach for a long time that extended to more h than 10 days free of infection. Then, the disease developed in the treated fruits, but slower than the control treatment, to one month. Under natural occurrence of infection, the fruits that were received spraying of different oils were still experienced a low degree of spoilage until 7 days of incubation. The fruits in control treatments were completely rotten after this time. Electron microscope approved the fungitoxicity of the essential oils for hyphae and conidia of all fungi. The essential oils caused clear deformation in the shape of hyphae, plasmolysis and distortion of them to indicates the complete death of the treated hyphae. GC-MS analysis approved the presence of some toxic constituents for fungi such as o-cymene, menthol, nerol, phellandrene, terpinene, menthone, carvone and thymol limonene, à-pinene and z-citral. The study recommends the application of essential oils especially lemon, thyme and mint, in a concentration of 2 %, to protect the peach fruits free from the fungal infection. Consequently, the shelf-life of this fruit will be prolonged during the handling and commercialization and the loss in the yield will be decreased.
