Abstract
The effects of preharvest melatonin treatment, applied as foliar spray at 0.1, 0.3 and 0.5 mM concentration at three key points of fruit development (pit hardening, initial colour changes and 3 days before harvesting), on crop yield and fruit quality properties at harvest was evaluated in three sweet cherry cultivars, ‘Prime Giant’, ‘Lapins’ and ‘Sweet Heart’, and two years, 2019 and 2020. The results showed that melatonin treatment had no effect on crop yield, except for the ‘Lapins’ cultivar, in which increases were found. However, decayed and cracked fruit percentage was decreased in all cultivars in 2020 when adverse weather conditions occurred and commercial crop yield was increased, especially for 0.3 mM dose. Fruit quality traits at harvest, such as fruit weight, colour, firmness, total soluble solids and titratable acidity, were enhanced by melatonin treatments in all sweet cherry cultivars and in both years. Moreover, bioactive compounds, such as total phenolics and total and individual anthocyanins, were also found at higher levels in fruit from melatonin-treated trees with respect to controls. Thus, taking into account all these effects, 0.3 mM melatonin foliar spray, at three key points of fruit developmental stages, could be a useful tool to improve crop yield and quality traits of sweet cherries, especially their content on bioactive compounds with antioxidant properties and health beneficial effects.
Highlights
Sweet cherry fruit (Prunus avium L.) is highly valued by consumers worldwide due to its excellent quality properties, mainly its colour, sugar and organic acid content, flavour, texture and juiciness [1,2,3]
Sweet cherry fruit are rich in bioactive compounds, namely phenolics and ascorbic acid, which are responsible of the health benefit effects attributed to sweet cherry consumption, the major ones being antimicrobial, antidiabetic, anticancer and anti-inflammatory effects, as well as neuroprotection and cardiovascular protection activity [4,5,6]
The percentage of unmarketable fruit from control trees in the 2020 experiment was very low for ‘Lapins’ and ‘Sweet Heart’ cultivars, they were significantly (p < 0.05) reduced by melatonin treatments and commercial yield was increased, the higher effect being observed with 0.3 mM concentration (Figure 2)
Summary
Sweet cherry fruit (Prunus avium L.) is highly valued by consumers worldwide due to its excellent quality properties, mainly its colour, sugar and organic acid content, flavour, texture and juiciness [1,2,3]. The effect of pre-harvest melatonin treatments on on-tree fruit ripening and quality traits at harvest has been evaluated in very few papers, and different effects have been reported depending on fruit species, concentration or application time. The application of 0.1 mM melatonin to tomato plants in the irrigation system increased lycopene and sugar content in fruits showing an acceleration of fruit ripening [13]. Enhanced apricot quality parameters at harvest and maintenance during storage, at chilling and not-chilling temperatures, have recently been reported in apricot fruits from melatonin-treated trees [15]. Melatonin treatment of ‘Mollar de Elche’ pomegranate trees increased fruit quality traits at harvest, including anthocyanin and phenolic content, and overall fruit quality was maintained during storage at higher levels as compared with fruit from control trees [16]
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