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

Abstract

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.

Effects of Melatonin Treatment on Sweet Cherry Tree Yield and Fruit Quality

“…The results of the present experiments showed, in general, an effect of 0.3 and 0.5 mM melatonin treatments on increasing fruit weight, although in the 'Lapins' cultivar, this effect was significant only for 0.5 mM dose in 2020 (Figure 3). Increases in fruit size have been recently reported in pomegranate fruit from melatonin-treated trees [22] as well as on grape berries [27], which were attributed to an increase of the fruit sink strength, leading the fruit to uptake more sugars and reach larger-size at harvest. Fruit colour, firmness and TSS and TA contents are also quality parameters highly valued by consumers in sweet cherry fruit and it is worth noting that all of them were found at higher levels in fruit from melatonin-treated trees than in controls (Table 2).…”

“…These effects were attributed to an increase in plant photosynthetic rate and leaf chlorophyll content. The yield of pomegranate tree was also increased by 0.1 mM melatonin preharvest treatment due to increases in fruit size and number of fruit harvested by tree [22]. Similarly, a 14% of crop yield was obtained in wellirrigated tomato plants when melatonin was applied at 30 and 50 days after transplanting, while this increase was 37% under water deficit stress [23].…”

Melatonin‐mediated postharvest quality and antioxidant properties of fresh fruits: A comprehensive meta‐analysis

“…Among the quality attributes of the postharvest life of fruits is respiration behavior; thus, respiration behavior shows a significant decline in melatonin applied to fruits. In this subgroup, the meta‐analysis result demonstrates reduction of respiration level in included studies (SMD −0.64, 95% CI [−0.97, −0.30]; sample size = 434; studies = 8; I 2 = 65%; p = .0002) (Bal, 2019; Gao et al., 2016; Li, Xu, et al., 2019; Liu, Chen, et al., 2019; Medina‐Santamarina, Serrano, et al., 2021; Onik et al., 2021; Wang, Zhang, et al., 2019; Zhai et al., 2018). The subgroup heterogeneity results in I 2 65%, thereby showing moderately less heterogeneity than other studies in the overall study subgroups, possibly due to low SMD.…”

“…Regarding the effect of melatonin on the fruit's weight loss, a statistically significant reduction of weight loss was shown in the test of overall effect (SMD −1.16, 95% CI [−1.80, −0.52]; sample size = 386; studies = 11; I 2 = 86%; p = .0004) (Bal, 2019, 2021; Gao et al., 2016; Lin et al., 2020; Liu, Zheng, et al., 2018; Medina‐Santamarina, Serrano, et al., 2021; Medina‐Santamarina, Zapata, et al., 2021; Onik et al., 2021; Rastegar et al., 2020; Wang et al., 2019; Wang, Wu, et al., 2019). Among included studies, Lin et al.…”

“…Ethylene concentration level in fruit is a critical factor in postharvest storage life. Ethylene synthesis level, effectively delayed in selected studies by melatonin treatment (SMD −0.83, 95% CI [−1.45, −0.22]; sample size = 502; studies = 8; I 2 = 90%; p = .008) (Hu et al., 2017; Liu, Chen, et al., 2019; Liu, Zheng, et al., 2018; Medina‐Santamarina, Serrano, et al., 2021; Onik et al., 2021; Sun et al., 2015; Xu et al., 2018; Zhai et al., 2018). In the most of the included studies, melatonin highly reduced ethylene content.…”