Calcium (Ca) is a major plant nutrient that affects cell wall and plasma membrane formation and plays a key role in plant growth, biomass production, and function. Ca can be used to decrease fruit decay and increase firmness and shelf life. Different sources and concentrations of foliar-applied Ca were examined for the effects on nutrient concentration and growth of ‘Eksotika II’ papaya (Carica papaya) plants. Papaya seedlings were established in pots and irrigated with a standard nutrient solution in a net house. Four preharvest sprays were applied as foliar applications with three different sources of Ca {calcium chloride [CaCl2], calcium nitrate [Ca(NO3)2], and calcium propionate [Ca(C2H5COO)2]} at four concentrations (0, 60, 120, and 180 mg·L−1). Plant Ca concentration was unaffected by the different Ca sources. However, increased Ca concentration applied to the leaves enhanced plant accumulation of phosphorous and Ca in the plant, but decreased potassium (K) and magnesium (Mg) concentrations in the tissues. Plants that received Ca at 180 mg·L−1 had greater height and diameter than control plants. In a field trial with mature trees, preharvest applications of Ca (0, 4000, and 5400 mg·L−1) in the form of CaCl2 showed that increasing concentrations improved fruit Ca concentration, texture, and flavor; and decreased weight loss, Mg content, and apparent disease incidence of the fruit.

Calcium chloride, especially at higher concentrations, is effective in maintaining papaya fruit quality during ambient storage. © 2015 Society of Chemical Industry.

BACKGROUND Sapota is a popular tropical fruit characterized by a very short postharvest life. Low‐temperature storage prolongs postharvest life of sapota fruit, but chilling injury symptoms can develop if the storage temperature is less than 14 °C. There have been no reports on the effects of postharvest melatonin application on the development of chilling injury in sapota fruit during cold storage. The objective of this study was to investigate the effects of different concentrations of postharvest melatonin application (0, 30, 60 and 90 μmol L−1) during cold storage (8 °C) for up to 30 days with an additional 1‐day shelf life at ambient temperature. RESULTS All melatonin treatments reduced chilling injury symptoms, reduced electrolyte leakage, malondialdehyde (MDA) content, H2O2 and superoxide anion (O2−), and increased proline content and the activity of superoxide dismutase (SOD), catalase (CAT) and γ‐aminobutyric acid (GABA), and reduced the activities of phospholipase D (PLD) and lipoxygenase (LOX) compared to the control. CONCLUSION Postharvest melatonin treatment could be a useful strategy for reducing chilling injury during cold storage and transport of sapota fruit. The results indicate that melatonin reduces chilling injury of sapota fruit through maintaining membrane integrity, SOD and CAT activities, and reducing PLD and LOX activities. © 2019 Society of Chemical Industry

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This research was conducted to evaluate the effects of calcium chloride (CaCl2) and calcium nitrate Ca(NO3)2 on nutrient concentrations and post-harvest quality of papaya fruits. In the first experiment, plant stem height increased significantly after Ca(NO3)2 application compared to CaCl2. Calcium content in peel and pulp for both sources significantly rose with increasing calcium concentrations, but there was a significantly higher content of calcium in fruit peel and pulp in the CaCl2 treatment. Magnesium and potassium in fruits decreased with increasing calcium concentrations. A reduction in anthracnose lesion diameter in infected fruit with increasing calcium was observed for both CaCl2 and Ca(NO3)2 treatments. Ethylene production\ud in fruits decreased with increasing calcium concentrations. In the second experiment, only CaCl2 was used as calcium source and results showed that calcium content in fruit peel and pulp significantly increased at higher CaCl2 levels, whereas ethylene production, anthracnose lesion diameter and magnesium contents decreased compared with control