113 Ethylene Mediates Responses of `Gala' Apple Fruit to Ionizing Irradiation

Abstract

Pre-climacteric `Gala' apple fruit treated with air (control) or 2 μmol·L–1 1-methylcyclopropene (MCP) were exposed to gamma irradiation at 0, 0.5, 1, or 1.5 kGy at 23 °C. Fruit were held at 20 °C for 3 weeks after treatment during which respiration rate, production of ethylene and other volatile compounds, fruit firmness, soluble solid content, titratable acidity, and irradiation injury were determined. MCP treatment reduced respiration and ethylene production and slowed loss of fruit firmness and titratable acidity. Irradiation induced increased respiration of MCP-treated fruit in a dosage-dependent fashion. Irradiation caused a decrease in ethylene production by control (non-MCP) fruit, and the magnitude of the decrease was dependent on irradiation dosage. Irradiation at 0.5, 1, and 1.5 kGy stimulated ethylene production of MCP-treated fruit for only 1 day after treatment. Irradiation induced internal browning and the injury severity increased with dosage. The severity and incidence of irradiation damage were higher in MCP-treated fruit than control fruit. The results indicate that ethylene is involved in mediating apple fruit responses to irradiation.