Effect of Preharvest Spraying of Selenium on Qualitative and Biochemical Characteristics of Grape cv. Fakhri (Vitis vinifera cv. Fakhri)

Demand for healthy and high-quality fruits has increased in the markets, and compositions such as vitamins, sugars, and anti-oxidant properties of fruits have attracted many consumers. Grapes contain phenols, flavonoids, anthocyanins, tannins and vitamins with high antioxidant properties. Antioxidants support biological systems such as proteins, amino acids, lipids, and DNA against oxidative damage produced by active oxygen species of ROS, resulting in reduction of cell damage and death, cardiovascular disease and cancers in the human body. Selenium is essential for humans and animals and should be fed through a diet, for this reason, FAO recommends entering selenium to agricultural products (especially fruits and vegetables). In recent years, selenium has been recognized as a useful element for plants that have been toxic at high concentrations but at desirable concentrations, it has positive antioxidant effects, increases growth and significantly affects seed germination. Selenium protects plants from several abiotic stresses such as heavy metal and arsenic, ultraviolet radiation, and biotic stress such as pathogens and pests. Selenium neutralizes oxidative stress interfering with lipid peroxidation, and accelerates gluthatione peroxidase (GSH-Px) activity, this phenomenon delay plant senescence and diminish postharvest losses. This element increases the yield and improves the quality of the fruits and vegetables. When Camelia oleifera plants were treated with selenium, cellular content of linoleic acid and sterol were elevated but oleic acid content diminished. Selenium treatment had a significant effect on preserving the sensory and the postharvest quality by decreasing respiration rate and ethylene biosynthesis in broccoli by diminishing phenylalanine ammonia-lyase (PAL) activity and ethylene production in lettuce and chicory. Foliar application of peach and pear trees with selenium, decelerated fruit softening rate and elongated shelf-life. Therefore, treatment of agricultural products with the appropriate amount of selenium can have a positive effect on the increase of the quality and enrichment of selenium in fruits and also play an important role in human health.

In order to investigate the effect of selenium as foliar application (0, 1, 2 and 3 mg L-1) on quality traits, antioxidant compounds and enrichment of grape cv. Fakhri, an experiment based on randomized complete block design with three replications in a vineyard (Kurdistan Povince, Ghorveh town) was performed. The 15-year-old vines were sprayed with selenium solution plus 0.1% of Twin 20 as surfactant until the leaves were completely wet (for each vine about 0.5 liter) at three stages of berry growth and development: Berry formation, Lag phase and veraison. A 1000 mg L -1 stock solutions (Made by the Belgian company CHEM-Lab, containing selenium ion Se+6) was used to prepare the desired solutions. At commercial fruit maturity stage (20° Brix), samples of fruits and leaves randomly were collected from treated and control vines and were immediately transferred to the postharvest physiology laboratory. Traits such as total chlorophyll, carotenoid, nitrogen, potassium, selenium  content of leaves and fruits, and also, total soluble solids, soluble sugars, titrable acidity, acidity (pH), vitamin C, phenol and flavonoids, antioxidant capacity in fruits and the berry weight were evaluated. Data were analyzed using SAS statistical software (SAS V.9.4), and means were compared by Duncan’s multiple range tests at the 5% of probability level.

Results showed positive effects of selenium treatment on evaluated traits. As a result, 2 mg L-1 of selenium increased photosynthetic pigments, nitrogen and leaf potassium, soluble solids, soluble sugars, vitamin C, total phenol, antioxidant capacity of fruits in comparison with untreated vines. The highest amount of titrable acidity, total fruit flavonoid and leaf selenium was recorded in vines treated with 3 mg L-1 selenium, whereas, this treatment had less effect on other traits. The highest amount of berry weight was obtained in 1 mg L-1 of selenium. However, none of the selenium treatments had significant effect on the juice acidity (pH). In general, the results showed a positive effect of selenium on improvement of antioxidant properties, quality and enrichment of grape, and 2 mg L-1 selenium with the highest effect on traits was identified as the best treatment. According to other researchers, foliar application of selenium in "Starking Delicious" apple cultivar was effective in enhancement of fruit selenium content and nutritional properties, postponing the flesh firmness decrease, and delaying fruit ripening resulting from less ethylene production, therefore significantly affecting apple fruit quality and storage life.