Retardation of Rutab Development of "Zaghloul" Dates and Enhancing Bunch Ripening Uniformity by Preharvest Application of Calcium and the Antiethylene Compound 1- Amino Cyclopropene, 1- Mcp.

Consumption of "Zaghloul" date fruits is highly demanded especially at the bisr stage. Date growers complain about the nonuniformity of the bunch that leads to greater loss of fruits either due to increase abscission prior harvest or deterioration of dates at the rutab stage. This study utilized the antiethlyene-action compound, namely 1-Methylcyclopropene along with calcium near maturity to inhibit the ripening (rutab development) of the dates that already have reached to the bisr stage, while the dates that were still near the end of the kimri stage continued to grow. Dates were preharvest sprayed during the two consecutive seasons 2015 and 2016 to the run off by using a hand sprayer. The treatments included the control (water), 1MCP at (50 ppm) known as Smart Fresh, as an aqueous spray, CaCl2 (2%, w/v), glycerol (1 %, v/v), 1-MCP followed by CaCl2, 1-MCP followed by CaCl2 plus glycerol, and finally CaCl2 plus glycerol at the same above concentrations. The whole bunches of all replications were harvested and sorted for their content of various ripening stages, namely bisr, semidry and rutab. The data revealed that almost all fruits were at the bisr stage at harvest time during the two seasons when they were treated first with 1MCP followed by CaCl2 plus glycerol, while the control bunches had significantly lower percentage of bisr dates as compared with the above treatments. Meanwhile, dates treated with 1MCP followed by CaCl2 plus glycerol had significantly greater anthocyanin content at harvest than that of the control in both seasons. Furthermore, all 1MCPtreated fruits had significantly lower leakage of electrolytes than that of the control dates. In conclusion, this study provided a practical evidence for the possibility of utilizing 1MCP as a mean of enhancing uniformity and delaying the progress towards the ripening of "Zaghloul" dates and extending the bisr stage. INTRODUCTION Date palm is one of the most important fruit crops in the world. The fruit has been described as a wealth of healthy components (Farag, 2016), since the fruit is loaded with sugars, nutrients and antioxidants. In spite of the rank of Egypt worldwide in the production of dates as the second country following Iran (Zaid and DeWet, 1999), there is still a great potential to increase the yield, enhance the quality and reduce the losses whether pre or postharvest. Major part of the loss could be attributed to the nonuniformity of date fruits within the same bunch. Dates advanced in their growth and development and ripening are subjected to abscission, since some fruits inside the bunch might reach to the rutab stage before the others. Eventhough rutab stage is accompanied by softening, it has been considered as the ripening stage. Many date fruits fall off the bunch once reached to ripening stage. Since date fruit growth curve is sigmoidal, the fruits may vary in their development stage by the end of the cell elongation stage known as Kimri stage. Thus, it is important to retard the progress towards ripening or entering the rutab phase. There has been a lack of research attempts to achieve fruit ripening uniformity within the same bunch. Few attempts focused only on preharvest spray of ethephon, the ethylene – releasing compound, in order to enhance fruit ripening (Farag and Kassem, 1998). The variations in dates growth and development greatly influence the response and the efficacy of sprayed chemicals. Fruit tissue variations influence their sensitivity to applied compounds in addition to the need to enhance the penetration of applied ethephon across the fruit cuticle (Farag and Kassem, 1998). "Zaghloul" date is one of the few cultivars that could be consumed at the bisr stage due to the conversion of soluble tannins to insoluble form, which reduces their astringency. It is important that the fruit is sweet and not bitter (Farag, 2016). There are few date cultivars that are suitable for marketing and consumption at the Khalal stage such as Zaghloul, Samany, Barhi and Khalas. They could have more potential of export to the European and other foreign markets to gain more profits. Thus, the increase in the percentage of Khalal fruits at harvest would mean better marketability and reduced loss. The use of the antiethylene compound, namely 1methyl cyclo propene (1-MCP) would result in delaying the ripening processes even in the presence of ethylene, since 1-MCP occupies the binding sites inside the fruit tissues, which gives the chance of dates near the end of the Kimri stage to grow and catch up with other fruits at more advanced stage of development. Calcium, on the other hand, was able to maintain the plasma membrane integrity and to preserve the structure of the cell walls in plant cells (Farag, 2010). Thus, the objectives of this study were to increase the uniformity of "Zaghloul" dates at harvest while maintaining the integrity and reducing the deterioration of tissues and providing the growers with a novelapplicable approach that utilizes 1MCP and calcium. MATERIALS AND METHODS This study was conducted during the two consecutive seasons 2015 and 2016 on "Zaghloul" date palm trees grown in a private orchard at Edko region, Behira governorate, Egypt. Trees were seventeen years old, nearly uniform, healthy, grown in a sandy soil, spaced at 7x7 m and received common horticulture practices. Four date palm trees were selected for implementing the investigation treatments and each one of these trees was exposed to all treatments (tree as a block). Each three bunches of each chosen tree at the tribal part of each tree were separately sprayed to the run off using a hand sprayer on 28 of August during 2015 and 2016, seasons (at the end of kimiri phase) with one of the following solutions:Control (water); 1-methylecyclopropene (MCP) at 50 ppm (v/v); calcium chloride at 2% (w/v); glycerol at 1% (v/v); MCP at 50 ppm and after dryness followed by calcium chloride at 2%; MCP at 50 ppm and after drying out followed by calcium chloride at 2 % (w/v) plus glycerol at 1 % (v/v)