Irradiation Reduces Superficial Scald by Downregulating Ethylene and α-Farnesene Biosynthetic Enzymes in ‘Granny Smith’ Apples

Superficial scald is a postharvest disorder of apples related to increased ethylene production in stored fruit which leads to α-farnesene accumulation and oxidation. Ionizing irradiation inhibits ethylene production and has been shown to reduce superficial scald, but this phenomenon has not been explored at the molecular level. The goal of this study was to determine the effect of irradiation on gene expression of enzymes related to ethylene and α-farnesene in ‘Granny Smith’ apples. Irradiation at 310 Gy controlled scald severity and incidence and inhibited the rise in AFS1 expression up to 90 d of cold storage followed by 7 d at room temperature, while 1000 Gy suppressed scald symptoms for either 90 and 180 d of cold storage, but showed internal browning. Irradiation at both doses reduced the formation of α-farnesene by more than 50% with concomitant decline of ACO enzyme activity and ethylene production as compared to the control, and suppressed the increase in ACS1 gene expression, but without the same effect on ACO1 gene. Irradiation treatment at 310 Gy and 1000 Gy may reduce superficial scald in ‘Granny Smith’ apples through inhibition of gene expression of enzymes related to ethylene and α-farnesene biosynthesis