Improvement of fruit quality in date palm

概要

Date palm (Phoenix dactylifera L.) has been cultivated in the Middle East and North Africa (MENA region) for millennia. Actually, 89% of dates are produced in these regions (Manickavasagan et al., 2012). Current world date production records 8.68 million tons. The Kingdom of Saudi Arabia (KSA) is the fourth largest producer of dates. With about 25 million date palm trees, KSA produces 1.3 million tons of dates annually, which represent 15% of the world date production (FAOSTAT, 2018). The date palm is one of the major crops that need to be improved from technical side to increase fruit quality, optimize production expenses and decrease its dependence on manpower. The ‘Sukkary’, ‘Khlass’, ‘Barni’, ‘Barhi’ and ‘Mejdool’ are some of the popular varieties cultivated in Saudi Arabia. In this study, I have mainly focused on Sukkery variety since it is a promising Saudi Arabian variety, with some comparison with other varieties.

1- Determination of fruit growth pattern of ‘Sukkary’, ‘Khlass’ and ‘Mejdool’
The growth physiology of date palm (Phoenix dactylifera) ‘Sukkary’, ‘Khlass’ and ‘Mejdool’ was studied by monitoring growth patterns in weight, volume, length and width. The variety specific characteristics were made clear in order to determine the approach on fruit maintenance such as thinning, water and nutrient supply, and so on, which might well lead to the quality improvement of date palm fruits.

2- Improvement of fruit quality of ‘Sukkary' by bunch cutting.
When different methods of thinning were compared on ‘Sukkary’, it was concluded that bunch cutting at the time of pollination to maintain 12 fruits per spikelet was the best alternative method to hand thinning. In addition to its contribution to the improvement of fruit size, it is also less expensive in terms of the manpower.

3- Effect of safflower and jasmine flower powder solution on the improvement of ‘Sukkary’ and ‘Khlass’ fruit color.
In an attempt to improve fruit color of ‘Sukkary’ and ‘Khlass’, I have implemented this experiment using solutions of Safflower Flower Powder at 300mg/liter or Cape Jasmine Fruit Powder at 25mg/liter to spray the bunches of ‘Sukkary’. The spray was done at the end of kimri and beginning of biser stage.

Safflower (Carthamus tinctorius) petals produce red (carthamin) and yellow (carthamidine) pigments which can be used as dying materials (Rudometova et al. 2001).

They contain about 30% of carthamidine pigment (Nagaraj et al. 2001) and 0.8% of carthamin (Kulkarni et al. 2001, Zhaomu and Lijie 2001). The yellow safflower pigment (carthamidine) is used as a natural food colorant, mainly in juice, jelly and candy (Shouchun et al. 1993), due to its high water solubility.

The water-soluble carotenoid fraction in Gardenia jasminoides Ellis (Cape Jasmine), which mainly consists of crocin and crocetin, is generally referred to as gardenia yellow. As an excellent natural food coloring material, gardenia yellow exhibits excellent water soluble properties and may therefore be used as a dying powder (Xu et al. 2016).

After sorting, Safflower Fruit Powder (300mg/liter) gave the best percentage of light color fruits in comparison with the control and Cape Jasmine Flower Powder at 25mg/liter.

4- Effect of four types of bunch covers on the improvement of fruit color of worldwide common ‘Mejdoor’.
In order to improve fruit color, four different bunch covers were examined: White non-woven bags, black non-woven bags, high-density polyethylene (HDPE) green mesh bags and Polyethylene Plastic bags. In contrast to ‘Sukkery’, darker skin color is preferred in case of ‘Mejdoor’.

After sorting, 54 % of the fruits were dark in color when black non-woven bags were used and 30 % were dark when Polyethylene Plastic bags were used. It was clear that 26 % were dark when HDPE green mesh was used and 20 % were dark when white non-woven bags.

5- Effect of different ethephon concentrations on shiss removal in ‘Sukkery’ and ‘Khlass’
After pollination, aborted fruits known as tri-carpel or shiss, remain on the bunch in most of the varieties. The remaining shiss fruits might waste water and nutrients. In Sukkary, they drop down at the end of biser stage, while remain in case of ‘Khlass’ until the harvest. Most of them remain biser and little could turn into tamar indicating less marketability. They can only be used as paste that has low profitability.

To try to get rid of shiss, I have sprayed ethephon at different concentrations on the bunches of ‘Sukkary’ and ‘Khlass’ after fruit-set. In ‘Khlass’, the ethephon concentration 800 ppm showed the optimum drop in shiss (81%), while in ‘Sukkary’, the concentration of 600 ppm was the optimum giving shiss drop equal to 44 % and fruit drop was 12% without normal fruit dropping.

6- Effect of five methods of storage in increasing the shelf-life of biser of ‘Barhi’
Most of date varieties are astringent at biser stage, and therefore they are not consumed at this stage. ‘Barhi’ is an exception as it has a very suitable biser. Because normal cold storage cannot keep ‘Barhi’ biser longer, date growers are obliged to sell it at a lower price in the local market when the production is at its peak and the supply is higher than the demand. In addition, date farmers targeting export are facing the transformation of biser into non-desirable rutab in ‘Barhi’ during the period of shipment that lasts more than 20 days in most of the cases.

Storage with two ethylene inhibitors (1-MCP and potassium permanganate) have been compared with oxygen absorber. All stored at 4℃ and sealed inside a plastic bag.

The storage inside plastic bag in a cold storage at 4℃, was the best in keeping ‘Barhi’ fruits as biser for long period, indicating less involvement of ethylene concerning to the biser state of ‘Barhi’ variety.

Conclusion
In this research, I was able to draw the fruit growth pattern of ‘Sukkary’, ‘Khlass’ and ‘Mejdool’. The growth pattern could be successfully used to look for the best method of thinning by bunch cutting and period of its application as an alternative to hand thinning that requires lot of manpower. Methods of improvement of fruit color in ‘Khlass’, ‘Sukkary’ and ‘Mejdool’ were also suggested. The shiss removal using ethephon has been suggested and the increase of ‘Barhi’ shelf-life for exportation and storage was made hopeful when applied with oxygen absorber.