Abstract: In order to control the occurrence of bitter pit in postharvest apple, Fuji apples were treated under water pressure with prohexadione-calcium, calcium nitrate and their combination. Changes in bitter pit incidence, total calcium and calcium species contents and antioxidant enzyme activities were investigated, and the mechanism underlying the control of bitter pit by prohexadione-calcium combined with calcium nitrate was discussed. The results showed that prohexadione-calcium alone could not alleviate the occurrence of bitter pit in Fuji apple, while the incidence of bitter pit in apples treated with calcium nitrate alone and in combination with prohexadione-calcium after storage for 40 days was decreased by 15.62% and 50.00%, respectively, when compared with the control. Furthermore, the combined treatment significantly increased the content of total calcium and water-soluble calcium in apple skin, and decreased the content of non-physiological active calcium such as calcium phosphate and calcium oxalate at the later stage of storage. In addition, the combined treatment significantly improved 2,2’-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) cation radical scavenging activity and superoxide dismutase activity, and inhibited the increase in malondialdehyde (MDA) content in apple skin, thus protecting against oxidative injury caused by calcium stress.

Key words: Fuji apple, bitter pit, prohexadione-calcium, calcium nitrate