Effects of foliar application of potassium sources, gibberellic acid and 2, 4- Dichlorofenoxy acetic acid on the qualitative and quantitative characteristics of Vitis vinifera cv. Askari

One of the cultivars of table grape in Iran is Vitis vinifera cv. Askari. But the smallness and non-uniformity of berry size have reduced its yield and attractiveness for consumers. Application of gibberellic acid, nutrients such as potassium as well as 2,4-D at the correct time can enhance the plant growth and fruit development. This study aimed to determine the most suitable gibberellic acid, 2,4-D, and potassium resources on quantitative and qualitative characteristics of Askari grape. This study was conducted on a research farm, on 30-year-old grapevine vines in the Koshkak region of Fars province of Iran in 2016. This experiment was arranged in a randomized complete block design with nine treatments and four replicates. Gibberellic acid at 50 mg/L, 2,4-D at 5, 10 and 20 mg/L, 10 mg/L 2,4-D + 50 mg/L GA3, 50 mg/L GA3 + 10 mg/L 2,4-D + 15 g/L K2SO4, 50 mg/L GA3 + 10 mg/L 2,4-D + 15 g/L KNO3, 50 mg/L GA3 + 10 mg/L 2,4-D + 15 g/L KCl and Distilled water as a control were used. The highest berry and cluster weights and lowest soluble solids content and total phenol were obtained in the treatment of 50 mg/L GA3+10 mg/L 2,4-D+15 g/L K2SO4 with mean of 2.58 g, 214 g and 14.25 ᵒBrix and 58.77 mg/kg, respectively. The lowest berry and cluster weights (1.70-118 g) were obtained from the 20 mg/L 2,4-D treatment. Also, the highest soluble solids content and anthocyanin were obtained from treatment of 20 mg/L 2,4-D with an average of 18.5 ᵒBrix and 41.71 mg/kg, respectively. Results have shown that the use of 50 mg/L of GA3 with 10 mg/L 2,4-D and the use of potassium sources, especially K2SO4 increased the yield and uniformity of the cluster and berry size.