Applied GA₅ , GA₄ , and GA_4/7 increase berry number per bunch, yield, and grape quality for winemaking in Vitis...

The gibberellins (GAs) GA₅ (inhibitor of GA₃ -oxidase), GA₄ (biologically active), GA_4/7 (commercially available mixture of Ga₄ and GA₇ ) prohexadione-calcium (ProCa, inhibitor of dioxygenases that render GAs bioactive, negative control), and GA₃ (positive control) were applied to bunches of Vitis vinifera cv. Malbec. Different techniques, doses, and timings were used in a 3-year field experiment. In year 1, GA₅ , ProCa, and GA₃ were applied at 35, 20, and 0 days before veraison (DBV) by dipping bunches three times. In year 2, single applications of GA₅ and GA₃ , also by immersion, were tested at 60, 45, and 30 DBV. In year 3, applications at 60 and 30 DBV of GA₅ , GA₄ , and a mixture of GA_4/7 were evaluated by dipping or spraying the bunches.

Vegetative growth, berry weight, and sugar content were unaffected by treatments. ProCa did not affect the yield with respect to water control, although it reduced the levels of phenolics in berry skins, an undesirable effect for winemaking. GA₅ , in the dose range 5-50 mg L^-1 , raised berry numbers, thereby augmenting bunch weight and skin phenolics at harvest, so increasing berry quality for winemaking. GA₄ and GA_4/7 produced similar benefits to GA₅ , with similar doses.

The applications of GA₅ , GA₄ , and GA_4/7 to developing grape berry bunches, in a range of concentrations and by dipping or spraying, increased berry numbers per bunch at harvest. The method can be used as a viticultural practice to improve the production and quality of wine grapes. © 2021 Society of Chemical Industry.