The Effect of Exogenous Application of Gibberellic Acid and Girdling on Characters of Grapes (Vitis vinifera) cv. Yaghoot

‘Yaghoot’ grape cultivar is the earliest cultivar known in the history of Iran. The main problem of this cultivar is the compactness and small size of its berries, under the influenced genes that are controlled mainly by Gibberellic Acid (GA3). Those undesirable traits reduce customer interest and profitability. To alleviate these problems, we used GA3 and carried out Girdling (G) to enhance the quantitative and qualitative characteristics. The GA3 treatment was used at four concentrations, i.e.: 0, 60, 90, and 120 mg/l, and was sprayed on plants three times (i.e.: 10 days before flowering, in the midst, and after flowering). The G treatment has achieved the proximity of the branch bases during the formation of berries. In this experiment, various morphological and biochemical traits were measured. The results exhibited that the GA3 and G treatments significantly positively affected the fruits' quantitative and qualitative characteristics. Both treatments were observed to increase the berry length, berry weight, berry diameter, berry width, cluster width, cluster length, cluster weight, titratable acidity, total soluble solids, proline, malondialdehyde, H2O2 content, total phenolic content, anthocyanin content, ascorbate content, flavonoids content, antioxidant capacity, catalase activity, peroxidase activity, polyphenol oxidase activity, superoxide dismutase activity, and ascorbate peroxidase activity. The interaction between the GA3 and G showed that they significantly increased the berry weight, proline content, antioxidant capacity, ascorbate content, peroxidase activity, polyphenol oxidase activity, ascorbate peroxidase activity, catalase activity, and superoxide dismutase activity. Those treatments are promising treatments that can help improve the quantitative and qualitative characteristics of ‘Yaghoot’ grapes.