The efficiency of Ca and K nitrate on the control of SERB damage in 'Thomson’ orange by modification of peel physical and chemical characteristics

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One of the most severe peel physiological disorders of orange fruits is Stem End Rind Breakdown (SERB), a severe postharvest physiological disorder. We expected foliar Ca and K application to reduce orange SERB by modifying several peel biochemical and physical characteristics. Therefore, one experiment (2018–2020) was designed in complete randomized blocks in four treatments with three replicates. Experimental treatments included foliar spray of (1) K nitrate; (2) Ca nitrate; (3) Ca, and K nitrate separately, with a time interval (Ca + K; combination of treatments 1 and 2); (4) control. The effects of treatments were evaluated on several parameters underlying fruit peel quality at harvest and intensity of SERB damage after 12 wk of fruit storage at 5 ◦C and 85% RH. The results showed that K-treated fruits had higher TSS and TSS/TA than other fruits. Also, the Ca treatments (including Ca and Ca + K treatments) increased Ca content in fruit peels and significantly decreased SERB damage and weight loss by 70% and 30%, respectively. In addition, Thomson orange peel obtained from Ca-treated trees (including Ca and Ca + K treatments) displayed elevated levels of pectin than other fruits. In contrast, the peels of fruits picked from trees sprayed with Ca, especially those treated with Ca + K, exhibited lower levels of total phenolic, antioxidant, and electrolyte leakage than other fruits. This study suggests that foliar application of Ca(NO3)2 and KNO3 during the fruit growth cycle while improving the internal quality of the fruit is an effective agronomical strategy that prolongs Thomson orange shelf life.