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

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 aminoethoxyvi-nylglycine (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, re-spectively. 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) concen-trations of fruit kept in air at 20 degrees C or stored at 0.5 degrees C for 21 days and then transferred to 20 degrees 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 degrees C for 21 days resulted in more rapid and higher ethylene production rates and IEC than for fruit kept at only 20 degrees 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.