Postharvest Application of Calcium and Magnesium to Honeydew and Netted Muskmelons: Effects on Tissue Ion Concentrations, Quality, and Senescence

Abstract

Muskmelon senescence is directly associated with a decline in hypodermal mesocarp membrane integrity and its Ca concentration, but infusing Ca into melons has been a problem. Fully ripened and abscised hybrid honeydew [Cucumis melo L. (Inodorus Group) `Honey Brew'] and netted muskmelon [Cucumis melo L. (Reticulatus Group) `Explorer'] fruit were submerged (dipped) 20 min at 25 ± 3 °C in a solution containing a Ca-chelate, a Mg-chelate, a combination of both chelates, or no mineral chelate. Following 10 or 24 days of cold storage (4 °C for `Explorer' and 10 C for `Honey Brew'), fruit were analyzed for mineral content and various senescence-related parameters. Abscised `Honey Brew' fruit dipped in either Ca-chelate or (Ca+Mg)-chelate and abscised `Explorer' fruit dipped in (Ca+Mg)-chelate, followed by 10 days cold storage, had hypodermal mesocarp Ca concentrations of at least 6.0 mg·g-1 dry weight. Maintaining hypodermal mesocarp tissue Ca concentrations at this level during postharvest storage, especially for fully ripe `Honey Brew' fruit, maintained membrane integrity and fruit firmness, and extended storage life 2.4-fold (i.e., to 24 days). The senescence regulatory effect of postharvest Ca-chelate treatments on abscised `Explorer' was highly variable, compared to `Honey Brew', which appeared to be due to the surface netting interfering with movement of Ca into the hypodermal mesocarp. Thus, postharvest Ca-chelate application to abscised `Honey Brew' fruit could delay fruit senescence in commercial storage, and open up new markets for fully ripened honeydew melons.