Interaction effect of gibberellic acid and potassium sulfate on soluble sugars and ‎dry matter, resveratrol content and antioxidant capacity of grape berries

In this research, the effect of foliar application of potassium sulfate (0, 1500 and 3000 mg/l) and gibberellic acid (0, 30, 60 and 90 mg/l) on yield and its components and qualitative and antioxidant capacity of ‘Bidaneh Sefid’ grapevine were investigated. This study was conducted factorially based on randomized complete block design in a vineyard at Malayer town. Vines were sprayed during three stages including of a week before bloom, two and four weeks after bloom. Based on results, the content of berry TSS, anthocyanin, ascorbic acid and antioxidant capacity was found to be highest in K2SO4 at 3000 mg/L in combination with GA3 at 30 ppm treatment. Also, the highest berry total phenol and flavonoid content were related to 3000 mg/L K2SO4 treated- vines in combined to GA3 at 60 and 90 mg/l, respectively. Moreover, the highest berry sucrose and glucose content were related to those vines treated with 3th levels of K2SO4 and 2th levels of GA3 combination treatment. Foliar application of K2SO4 improved berry resveratrol and viniferin concentration in GA3-treated vines and berry stilbenes increased with increased K2SO4 doses. The highest activity of catalase, guaiacol peroxidase and ascorbate peroxidase antioxidant enzymes were observed in vines treated with K2SO4 at 3000 mg/l in combination with GA3 at 90 mg/l. Totally, foliar application of K2SO4 especially at 3000 mg/l in combination with moderate doses of GA3 improved the yield, accumulated dry matter, increased the sugar content and the antioxidant capacity of the grape berries.