2017 ASHS Annual Conference

Irradiation has proven to be effective as a phytosanitary treatment for various fruit. It could be particularly useful for apple varieties that are sensitive to fumigation and when market conditions require a faster treatment than cold storage. However, irradiation produces reactive oxygen species that can elicit a stress response leading to increased respiration rate and associated changes in fruit quality. The objective of this work was to evaluate the physiological effect of irradiation (400 and 800 Gy) on fresh ‘Fuji’ apples harvested late in the season. ‘Fuji’ apples were arranged in a single layer in cardboard boxes and exposed to dual sided e-beam radiation. Following treatment, the fruit was stored at 1 ^oC for 7 days, to simulate transportation from California to Mexico, then for 7 days at 25 ^oC, to mimic distribution and retail conditions. Ethylene production was decreased by the 400 Gy treatment and particularly at 800 Gy. Conversely, treatment at 800 Gy increased the respiration rate of Fuji apples, more significantly during the cold storage and the first 3 days at room temperature. Despite the increased respiration, irradiation did not affect sucrose, glucose, fructose and sorbitol concentrations. Irradiation treatments increased electrolyte leakage significantly (P<0.05) from 9% (control) to 12% (400 Gy) and 16% (800 Gy). The MDA content in the cortical tissue of apples treated at 800 Gy was significantly higher (P<0.05) than 400 Gy on day 7, and showed the highest value (7.14 nmol.g^-1) at the end of the second week. Thus, while irradiation at 800 Gy resulted in an increase in physiological indicators of stress in late harvested ‘Fuji’ apples, these responses, including increased respiration rate, do not seem to be influenced by a decrease in ethylene production. This suggests that irradiation affected the activity of one or more enzymes involved in ethylene biosynthesis.