عنوان مقاله [English]
Introduction: Grape (Vitis vinifera L.) is one of the most important fruits cultivated in many areas with different climates all over the world. Being rich in antioxidants, flavonoids, anthocyanins and phenolic acids, grape is highly regarded in terms of economic value. Salicylic acid is one of the compounds which have been used in recent years for improving the physicochemical properties of many fruits. Application of salicylic acid increases the shelf life of crops by inhibiting ethylene production and respiration, as well as by reducing the activity of some enzymes softening the cell wall. Furthermore, salicylic acid results in the enhancement of phenolic compounds production by increasing the activity of some enzymes such as phenylalanine ammonia-lyase.
Materials and Methods: The experiment was performed on 13-year-old grapes cv. Shahroodi cultivated with the space of 2m × 2m and head-training system in Shahrood County, Semnan province, in 2014. A number of 60 grapevines uniform in age and growth characteristics were selected. Salicylic acid solution was prepared at concentrations of 0 (control), 1, 2, 3 mM by dissolving in ethanol and a few drops of Tween 20 for better penetration. The prepared solution was sprayed two weeks after the fruit set stage (when berries were at pea-sized stage with the diameter of 4 to 5 mm). The experimental design used in in this experiment was a randomized complete block design with three replications. After harvesting and transporting of fruits to the laboratory, different characteristics such as yield, sugar and acid content, firmness and content of phenolic compounds were measured. Furthermore, chlorophyll content (a, b and total) and carotenoids in leaves were measured simultaneously at the harvest time of fruit.
Results: As the results obtained from analysis of variance showed, application of salicylic acid caused significant differences in the measured characteristics, so that the use of this compound resulted in the improvement of physical and biochemical quality of the treated clusters. Comparison of treatments means showed that using 2 mM salicylic acid brought about a significant effect on the amount of chlorophyll (a, b and total) and carotenoids compared to other treatments, especially control. Salicylic acid application caused a reduction in pH and soluble solids, and increase in firmness, 100-berry weight and yield. Furthermore, salicylic acid treatments enhanced significantly organic acids and reduced reducing sugars, so that the maximum amount of tartaric acid in fruits was obtained in the treatment containing 2 mM salicylic acid with an average of 0.66; while the lowest amount of tartaric acid was related to the control treatment with an average of 0.52, indicating the reduction of transpiration and consumption of organic acids in the mentioned treatment. The greatest and lowest amounts of reducing sugars were observed in control (14%/74) and the treatment of 2 mM salicylic acid (13%/60), respectively. Increasing the concentration of salicylic acid up to 2 mM resulted in the enhancement of anthocyanins and phenolic compounds contents, but higher concentrations (more than 2 mM) reduced the amounts of these compounds in treated fruits.
Conclusion: Pre-harvest use of salicylic acid could have a positive effect on the improvement of qualitative and quantitative characteristics of grape cv. Shahroodi. However, further comprehensive studies are needed to be conducted to recommend this compound to the growers of fruit trees.