Exogenous Application of Melatonin and Methyl Jasmonate as a Pre-Harvest Treatment Enhances Growth of Barhi Date Palm Trees, Prolongs Storability, and Maintains Quality of Their Fruits under Storage Conditions.

Waleed M E Fekry,Younes M Rashad,Ibrahim A Alaraidh,Taha Mehany

doi:10.3390/plants11010096

Abstract

Fresh date palm fruits (cv. Barhi) have received much attention due to their sweet taste and popularity in marketing. There is a critical need to prolong their storability, as well as maintain their quality during the postharvest and marketing periods. In this study, the effects of spraying date palm trees with melatonin (Mt) and/or methyl jasmonate (Mj) at 10, 20, and 50 ppm, on their growth and yield were investigated. In addition, impacts on quality and storability of the fruits were also studied. In general, application of Mt was mostly more effective than that of Mj, even at 50 ppm, with regard to all evaluated parameters. However, the dual treatment at 50 ppm recorded the highest relative chlorophyll and nutrient content in date palm leaves, as well as the yield and its components. Regarding the date palm fruits stored at 4 °C for 28 days, this dual treatment recorded the lowest weight loss and fruit decay values (0.14 and 2%, respectively), the highest firmness (6 g·cm−2), total soluble solids content (36 °Brix), total sugar content (32.5 g/100 g fresh weight), and the lowest total acidity (0.16 g citric acid/100 mL juice). Moreover, the highest total phenolic content and activity of peroxidase and polyphenol oxidase enzymes in the stored fruits were also recorded for the dual treatment. In contrast to the untreated fruits, scanning electron microscopy observations showed that the sprayed fruits had a very good microstructure, showing intact and thick exocarp tissue with a dense layer of epicuticular wax. The mesocarp tissue showed a normal and clear cellular framework with well organized and arranged cells, after 28 days storage at 4 °C. Based on these results, we can conclude that application of the dual treatment (Mt + Mj) at 50 ppm is a promising way to prolong the storability of date palm fruits and maintain their quality during storage periods.

Highlights

Date palm (Phoenix dactylifera L.) is one of the most important crops cultivated in the Middle East region, especially the Arabian Peninsula and North Africa countries
We can conclude that application of the dual treatment (Mt + methyl jasmonate (Mj)) at 50 ppm is a promising way to prolong the storability of date palm fruits and maintain their quality during storage periods
The obtained results showed that all applied treatments led to a significant increase in the relative chlorophyll content in date palm leaves in both seasons, compared with the untreated control leaves

Summary

Introduction

Date palm (Phoenix dactylifera L.) is one of the most important crops cultivated in the Middle East region, especially the Arabian Peninsula and North Africa countries. Date palm fruits have a high nutritional value, containing up to 88% carbohydrate, 5.6% protein, 11.5% fiber, as well as various minerals and vitamins. Their seeds contain up to 58.8% of oleic acid, which makes them an economic source for oleic acid production [3]. Fruits of date palm have five stages of developmental and ripening stages: Hababouk, Kimri, Khalal, Rutab, and Tamer, respectively. Barhi dates are more favored and higher in marketing price at the Khalal stage compared to the Rutab and Tamer stages [5]. There is a critical need to prolong their storability, as well as maintain their quality during the postharvest and marketing periods

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Results

Conclusion