Effects of Gibberellic Acid on Quantitative and Qualitative Traits of ʻSultana’ Seedless Grape Fruit

In order to evaluate the effect of gibberellic acid on yield and fruit quality of grapes, an experiment was conducted in a completely randomized design on five-year-old vines of ʻSultanaʼ seedless cultivar. First at the stage of cluster emergence, all of the vines were sprayed with 10 mg/l of gibberellic acid except control and then, at the second stage, different gibberellic acid treatments including 0, 10, 20, 30, 40 and 50 mg/l concentrations were applied when the berries were at 1-2 mm diameter. Exogenous gibberellic acid application significantly increased the weight, volume, length and diameter of the berries compared to the control. Cluster axis length and cluster weight as well as total vine yield were also significantly improved by gibberellic acid treatments. The reduction of length to diameter ratio of berries due to gibberellic acid resulted in the production of rounder berries than the control. Traits such as pH and volumetric mass (weight to volume ratio) of berries were not affected by gibberellic acid. As the yield increased, the process of fruit ripening was delayed by the gibberellic acid. Due to gibberellic acid treatment, the soluble solids content (SSC) of fruit decreased and the total acid content of fruit extract increased.