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.

The effects of preharvest melatonin treatment on apricot crop yield and fruit quality properties at harvest and during storage have not yet been investigated. Apricot trees, of the ‘Colorado’ and ‘Mikado’ cultivars, were sprayed with 0.1 mM melatonin at three key points of fruit development. Fruit were harvested at commercial ripening stage and yield was higher in melatonin treated trees than in the controls. Fruit were stored at 1 and 8 °C for 21 and 28 days, respectively. Samples were taken weekly and left at 20 °C for 1 day. Weight losses, as well as reduction in firmness and acidity, were delayed in fruits from melatonin treated trees, showing an effect of treatment on delaying the postharvest ripening process, which was attributed to a reduced ethylene production in both cultivars and at both storage temperatures. In addition, chilling injury symptoms were observed in apricots stored at 1 °C, which were reduced by preharvest melatonin treatment. Moreover, apricot from melatonin-treated fruit retained higher total phenolic content than the controls after 14 days of storage, although the phenolic profile was not affected by treatment. Thus, melatonin could be a useful tool for practical purposes to improve apricot crop yield and maintain fruit quality properties during storage.

The effect of melatonin pomegranate tree treatments on fruit quality and bioactive compounds with antioxidant activity at harvest and during storage at 10 °C for 60 days was assayed in two consecutive years, 2019 and 2020. In the first year, trees were treated with 0.1, 0.3 and 0.5 mM of melatonin along the developmental fruit growth cycle, and results showed that bioactive compounds (total phenolics and total and individual anthocyanins) and antioxidant activity at harvest were higher in fruits from melatonin-treated trees than in controls. Other fruit quality parameters, such as firmness, total soluble solids and aril red colour, were also increased as a consequence of melatonin treatment. In fruit from control tress, firmness and acidity levels decreased during storage, while increases occurred on total soluble solids, leading to fruit quality reductions. These changes were delayed, and even maintenance of total acidity was observed, in fruit from melatonin-treated trees with respect to controls, resulting in a fruit shelf-life increase. Moreover, concentration of phenolics and anthocyanins and antioxidant activity were maintained at higher levels in treated than in control fruits during the whole storage period. In general, all the mentioned effects were found at the highest level with the 0.1 mM melatonin dose, and then it was selected for repeating the experiment in the second year and results of the first year were confirmed. Thus, 0.1 mM melatonin treatment could be a useful tool to enhance aril content on bioactive compounds with antioxidant activity and health beneficial effects and to improve quality traits of pomegranate fruit, at harvest and during postharvest storage.

The effects of oxalic acid (OA) applied in preharvest on pomegranate crop yield and quality properties have not yet been investigated. Pomegranate trees were treated with OA at 1, 5, and 10 mM along the developmental growth cycle during 2016, from full blossom until harvest, and the fruit diameter was recorded monthly. The yield was significantly higher in OA-treated pomegranate trees, the on-tree ripening process being promoted in a concentration-dependent manner. With respect to quality traits, OA at 10 mM showed better results in terms of firmness, external color due to a red color enhancement, and respiration rate and sensory attributes. Then, a second-year experiment was performed with OA at 10 mM, and crop yield and fruit quality results were confirmed. In addition, an increase in glucose and total acidity, specifically malic and ascorbic acids, was observed in OA 10 mM-treated pomegranate fruit. Bioactive compounds were also higher in OA-treated fruit than control, the 10 mM concentration being the most effective in increasing total phenolics, total anthocyanins, and total antioxidant activity. Overall, results suggest that OA applied at 10 mM as preharvest treatment could be an effective tool to enhance pomegranate crop and quality and to improve the content of health-related compounds.

Consumers demand the use of eco-friendly fungicides to treat fruit and vegetables and governmental authorities have unauthorized the application of chemical antifungals for the efficient control of sour rot. In the present research, the microwave irradiation (MW) method was used to encapsulate thymol into 2-hydroxylpropyl-beta-cyclodextrin (HP-β-CD) and the effect of these HP-β-CD on controlling sour rot in citrus fruit, caused by Geotrichum citri-aurantii, was evaluated. Amounts of 25 and 50 mM of HP-β-CD-thymol were used, and compared with propiconazole, to control the decay of inoculated lemon fruit. The treatments were performed in curative and preventive experiments. The incidence and severity of Geotrichum citri-aurantii in 25 and 50 mM HP-β-CD-thymol-treated fruit were reduced in both experiments. The preventive 50 mM HP-β-CD-thymol treatment showed the best effect, reducing the sour rot, respiration rate and fruit weight loss during storage at 20 °C. HP-β-CD-thymol increased polyphenol concentration and the activity of antioxidant enzymes, such as catalase (CAT), ascorbate peroxidase (APX) and peroxidase (POD) in lemon peel, and the highest effects were found with the 50-mM dose. In conclusion, the results show that the use of thymol encapsulated by MW into HP-β-CD could be an effective and sustainable tool, a substitute to the synthetic fungicides, for G. citri-auriantii control in citrus fruit.

Rainfall occurring during the developmental stages of sweet cherries on the tree can lead to significant preharvest losses, primarily due to fruit cracking. Certain cultivars exhibit a higher susceptibility to such losses, particularly when persistent rains coincide with advanced phenological stages. The current study aims to investigate the efficacy of preharvest methyl jasmonate (MeJA) applications at harvest and during distinct developmental ripening stages in mitigating sweet cherry cracking at harvest and on-tree ripening. Preharvest foliar applications of 0.5 mM MeJA were applied across various sweet cherry cultivars, including ‘Prime Giant’, ‘Early Lory’, ‘Sweetheart’, and ‘Staccato’. By conducting this experiment over four growing seasons, we evaluated the impact of this natural elicitor on the cracking tolerance of these cultivars. The results of our analysis indicate that MeJA preharvest treatments effectively reduce fruit cracking, enhancing abiotic stress tolerance. Additionally, these treatments induce a general delay in fruit ripening on the tree across the examined cultivars. This delayed ripening effect is reflected in several quality parameters at harvest, such as the fruit firmness, external colour, total soluble solids, and total acidity. These parameters in the MeJA-treated fruit were delayed compared to the control fruit or remained unaffected for the total acidity. Conversely, the MeJA treatments delayed the accumulation of total polyphenols, exhibiting a minimal impact on reducing pedicel browning. The enhanced tolerance to cracking and delayed ripening attributed to the MeJA preharvest treatments could be helpful for plot management. Consequently, these MeJA-based preharvest treatments hold potential as valuable tools in adapting to climate change and mitigating abiotic stress in sweet cherry.