Melatonin limited ethylene production, softening and reduced physiology disorder in pear (Pyrus communis L.) fruit during senescence

Some pear (Pyrus communis L.) fruit show a certain resistance to ripening. Thus, postharvest cold storage is commonly used to accelerate their ripening process by promoting ethylene production. However, the enhanced ethylene biosynthesis also accelerates pear fruit senescence. Here, the effects of melatonin on the senescence process in pear fruit was investigated. In a rapidly softening pear 'Starkrimson', melatonin delayed the ethylene burst. In 'Abbé Fetel' and 'Red Anjou', normally softening pears, melatonin inhibited ethylene production during the entire senescence process. The limited ethylene production resulted in a lower loss of firmness in melatonin-treated fruit than in water treated fruit. PcPG, a major cell wall degradation-related gene, was inhibited by melatonin in all three cultivars. The expressions of ethylene biosynthesis genes PcACS1 and PcACO1 are correlated with the senescence process. The former was inhibited by melatonin in 'Starkrimson', both were inhibited in 'Red Anjou', but neither was inhibited in 'Abbé Fetel'. Moreover, the antioxidant systems in 'Starkrimson' and 'Abbé Fetel' were enhanced by melatonin and their fruit did not undergo water soaking or core browning. Thus, melatonin has the potential to retain the commercial value of postharvest pear fruit and delay senescence by limiting ethylene production and the reactive oxygen burst.