Melatonin Treatment of Pomegranate Trees Increases Crop Yield and Quality Parameters at Harvest and during Storage

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 degrees 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.