Efficacy of some calcium salts foliar spray on growth and biochemical parameters of jujube fruit (Ziziphus jujuba Mill.)

  South Khorasan province is the most important area of jujube fruit production in Iran. Fresh jujube fruit destroys in a short time at ambient temperature. Normally about one week after harvesting, a considerable loss occurs in picked fruits. Plant nutrition, during growth and developmental stages influence the quality of many fruits. Calcium is one of the most important elements that can affect quantity, quality, storability and market of many horticultural crops. Although South Khorasan province is located in arid areas, it has lime soils with enough calcium for plant growth and development. However, due to low mobility of calcium from soil to plant, calcium deficiency is common in horticultural plants. Thus, pre-harvest spray with minerals like calcium salts can be useful for reducing postharvest losses during handling and storage. Therefore, the aim of this research was to evaluate the effect of different calcium salts spray on physicochemical properties and quality of fresh jujube fruit. Twenty jujube trees, eight years old, were sprayed with calcium salts twice, mid of June and early in July 2016 in a commercial orchard in Birjand, South Khorasan province. Experimental treatments were distilled water (control), calcium chloride (0.5 and 1%) and calcium nitrate (0.5 and 1%). Sprays were done at two stages of fruit growth and development, cell division (3 mm fruit diameter), and 20 days later in full cell enlargement stage. Fresh fruit was harvested at a crisp mature (white-red) stage early in August. The experiment was conducted in a completely randomised block design with four replications, and each replicate included 500 g of fresh fruit. Data were analysed using SAS program (ver. 8) and comparison of means was made with LSD test at 1 and 5% probability. Physiochemical properties of harvested fruit including fresh fruit weight, dry matter, fruit length and diameter, firmness, total soluble solids, pH, carotenoids, total phenol, and calcium content were evaluated. The results showed that calcium nitrate application at 0.5% significantly increased fruit fresh weight, dry matter and fruit length and diameter compared to control. Also, fruits that were sprayed with calcium chloride at 0.5% concentration had higher firmness, carotenoids and total phenol. The highest total soluble solids and calcium content values were obtained in treated fruit with calcium chloride (1%). Although different calcium salts spray had no significant effect on juice pH. In general, it can be concluded that physical fruit parameters were affected by calcium nitrate, while calcium chloride spray had a greater impact on chemical and nutritional quality aspects of fruit. Although calcium chloride at 0.5% was more effective on chemical factors, however, it was not significantly different with calcium chloride 1% treatment. Among different treatments, calcium nitrate at 0.5% had the highest effect on physical properties of jujube fruit. Therefore, it can be concluded that spraying of jujube fruit trees during fruit growth and developmental stages with both calcium salts at 0.5% concentration have beneficial effects as they improve the most important physical and chemical parameters of fresh jujube fruit.