Harvest Maturity and Preharvest Aminoethoxyvinylglycine Treatment Effects on Cold-induced Ethylene Production of ‘Gala’ Apples

Abstract

Cold storage is a commonly adopted technology to maintain quality and extend shelf life; however, depending on the cultivar, ethylene production can be enhanced by short-term cold treatments. In this study, index of absorbance difference (IAD) values, which reflect skin chlorophyll concentrations of cold-influenced ripening patterns, of ‘Gala’ apples were investigated. Fruit that were untreated or treated with aminoethoxyvinylglycine (AVG), which is a plant growth regulator that inhibits ethylene production of fruit, were harvested from a commercial orchard. Two IAD value categories 0.6 to 0.8 and 0.2 to 0.4 were chosen from a single harvest in 2019, whereas in 2020, the fruit in categories 0.6 to 0.8 and 0.2 to 0.4 were chosen for two harvests separated by 1 week, respectively. In 2019, only ethylene production was measured. In 2020, ethylene production, respiration, internal ethylene concentration (IEC), flesh firmness, 1-aminocyclopropane-1-carboxylate (ACC), and malonyl 1-aminocyclopropane-1-carboxylate (MACC) concentrations of fruit kept in air at 20 °C or stored at 0.5 °C for 21 days and then transferred to 20 °C were measured. The results were different from those described in the literature for cold-enhanced ethylene production of ‘Gala’ apples. Although ethylene production occurred without cold exposure of untreated fruit, exposure of fruit to 0.5 °C for 21 days resulted in more rapid and higher ethylene production rates and IEC than for fruit kept at only 20 °C. Ethylene production was suppressed by the preharvest AVG treatment, especially in 2020. The rates of respiration and softening of non-AVG treated fruit were enhanced by cold treatment. The effects of cold treatment were more significant for less mature fruit as indicated by higher IAD values.