Inhibitory Effects of Pre-harvest Spraying Diethyl Aminoethyl Hexanoate on the Disease Occurrence in Longan Fruit during Postharvest Storage and Its Mechanism

In order to elucidate the influences of pre-harvest spraying diethyl aminoethyl hexanoate (DA-6) on the disease occurrence in longan fruit during postharvest storage and its possible mechanism, fruit of ‘Fuyan’ longan at 70, 90 and 110 days after full bloom was sprayed with DA-6 solution at the concentration of 10 mg/kg, and the fruit sprayed with distilled water served as control. The harvested longan fruit were stored at (28±1) ºC. During storage, the index of longan fruit disease, the contents of lignin and total phenolics, the activities of phenylalnine ammonia-lyase (PAL), polyphenol oxidase (PPO), peroxidase (POD), chitinase (CHI) and β-1,3-glucanase (GLU) in longan pericarp were evaluated. When stored for 6 d, the fruit disease index in 10 mg/kg DA-6-treated longan was 11.59% lower than control longans. The results also indicated that, contrasted to the control samples, during postharvest storage, pre-harvest spraying DA-6 could lower index of fruit disease, reduce activities of PPO and POD, but retain higher activities of PAL, CHI and GLU, as well as maintain higher levels of lignin and total phenolics. These findings suggested that pre-harvest spraying DA-6 could effectively suppress disease development of postharvest longan fruit, which was due to DA-6 induced-the enhanced activities of disease resistance related-enzymes and the reduced activities of phenols oxidation related-enzymes, the increased levels of disease-resistant substances, and then the enhanced disease resistance.