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.

With the aim to study the effect of melatonin treatment of pomegranate trees on crop yield and fruit quality at harvest and during storage, two experiments were carried out in two consecutive years: 2017 and 2018. In the first year, trees were treated with melatonin (at 0.1 and 1 mM) along the developmental growth cycle and fruit quality parameters were evaluated at harvest and during storage at 10 °C for 90 days. Treatments with melatonin led to an increase of crop yield (number of fruits per tree and kg per tree), as well as higher fruit quality attributes, such as fruit size (diameter and weight), color, total soluble solids (TSS), and total acidity (TA), especially with the 0.1 mM dose. Then, in the second year, melatonin at 0.1 mM was selected for repeating the pre-harvest treatments with similar results in terms of crop yield and fruit quality parameters. During storage, pomegranate fruit treated with 0.1 mM melatonin maintained higher quality attributes than controls, such as TSS, TA, and firmness and lower weight losses were observed in fruit from treated trees, in both trials. In addition, the content of the major sugars (glucose and fructose) and organic acids (malic, succinic and ascorbic acid) were higher in melatonin-treated than in non-treated fruit. These results suggest that pre-harvest melatonin treatment could be a useful tool to increase pomegranate crop yield as well as fruit quality parameters at harvest and their maintenance during storage due to an effect of melatonin on reducing the postharvest ripening process.

The main aim of this study was to evaluate the effect of salicylic acid (SA) as a preharvest treatment on crop yield throughout the crop cycle of green pepper fruit as well as on its quality parameters, including functional quality, at harvest and during 21 days of storage at 7 °C. Thus, ‘Herminio’ pepper plants were treated with SA at 0.5, 1 and 5 mM, and higher crop yield (kg per plant, number of fruits per plant and average fruit weight) and quality parameters (firmness, green color and total acidity) at harvest were obtained with the 0.5 mM dose, as well as greater phenolic compounds content and total antioxidant activity. These quality traits and functional quality were also maintained at higher levels for this treatment than in controls during postharvest storage, leading to a delay of fruit quality losses. In addition, the decay incidence for 0.5 mM SA-treated pepper fruits reached a ca. value of 2% at the end of the storage, which was lower than untreated fruits (16.6%). These results suggest that preharvest application of SA at low doses tested on pepper plants could be a useful tool to increase crop yield and fruit quality parameters at harvest and maintain them during storage, delaying quality losses and decay incidence.