Effects of Exogenous Gibberellic Acid on Yield Components of ‘Askari’ Grape

Abstract The most important commercial use of gibberellin in horticulture is to improve the yield and marketability of table grapes. This experiment was conducted in order to evaluate the effect of different concentrations of gibberellic acid on yield components of five-year-old ʻAskariʼ seedless grapevines, based on a randomized complete block design. Gibberellic acid was sprayed on the foliage and clusters in two stages: First 10 mg/L of gibberellic acid was applied on all trees except the control, at the stage of cluster emergence (2-3 cm in length) and then, 0, 10, 20, 30, 40 and 50 mg/L concentrations were used when the berries were at 1-2 mm diameter. Exogenous gibberellic acid application led to the significant increase in the average weight, volume, length and diameter of the berries compared to the control. Mean weight of cluster as well as vine total yield were also improved significantly by gibberellic acid treatments. The pH of fruit extract was increased by gibberellic acid treatment. Exogenous gibberellic acid decreased the soluble solids content of berries, but total acid content of berries was increased by gibberellic acid treatments. Gibberellic acid application had no significant effect on berry shape index (length/diameter ratio), berry volumetric mass (weight/volume ratio) and cluster axis length. Based on the results of this study, foliar application of 10 mg/L gibberellic acid increases the yield of ʻAskariʼ cultivar and is potent to be used by the grape growers.