2019 ASHS Annual Conference

Superficial scald is a physiological disorder characterized by skin browning that appears during or after storage of ‘Granny Smith’ apples. Currently, the disorder is controlled by reducing a-farnesene oxidation with antioxidant diphenylamine (DPA). The mechanism for scald development is not fully understood, but it is hypothesized that scald formation is related to increased ethylene production. In apples, low dose irradiation induced ethylene reduction appears to be directly related to prevention of superficial scald. However, the molecular basis of such an irradiation-induced effect is not known. In this study, effort was made to better understand the molecular basis of the decrease in superficial scald and ethylene production in ‘Granny Smith’ apples after treatment with gamma irradiation. Apple fruit were exposed to radiation treatment either at 310 Gy or 1000 Gy and ethylene production, ACC oxidase enzyme activity and expression of the genes responsible for ethylene biosynthesis were measured after 0, 90, and 180 days of storage. Ethylene production of irradiated apples was lower compared to control. No difference was observed in ACC oxidase activity at day 0, but irradiation at 310 Gy and 1000 Gy reduced enzyme activity at days 90 and 180. In contrast, increased expression of ACC oxidase 1 (ACO1) and ACC oxidase 2 (ACO2) was observed at day 90 for apple fruit treated with radiation at 310 Gy. ACC synthase 3 (ACS3) was not significantly affected by radiation treatment. Gene expression did not correlate with ethylene production or ACC oxidase enzyme activity. Our results indicate that irradiation had different effects on gene expression and enzyme activity, and subsequently ethylene production. Additionally, factors other than gene expression affect ethylene biosynthesis.