GA3 (Gibberellic acid) is one of the important endogenous hormones that promote plant growth and development. In plants, GA3 is synthesized in germinating seeds, young shoots, growing leaves, blooming flowers, stamens, pollen grains, fruits, and roots. GA3 synthesized in the roots moves upward, while that produced at the apex moves downward. Its transport occurs through the phloem, and the speed is comparable to that of photosynthate translocation. Exogenous GA3 exhibits multiple physiological effects similar to those of endogenous gibberellins, such as altering the ratio of female to male flowers in certain crops, inducing parthenocarpy, accelerating the growth of some fruits, and promoting fruit set; breaking seed dormancy, advancing germination, accelerating stem elongation and bolting in some plants; increasing leaf area, promoting young shoot growth, facilitating metabolite accumulation in the phloem, and activating the cambium; and inhibiting maturation, senescence, lateral bud dormancy, and tuber formation. Regulators such as paclobutrazol and daminozide can inhibit the biosynthesis of GA3 in plants, and GA3 acts as an effective antagonist to these regulators.
① During the fruit set stage of grapes, GA3 can increase the levels of gibberellins and auxins in young fruits, prevent the formation of abscission layers, and attract nutrients to the young fruits, thereby improving fruit set rate. The recommended concentration typically ranges from 12.5 to 100 mg/L.
② Spraying or dipping the clusters of certain grape varieties from full bloom to within 5 days after petal fall significantly increases berry size. This is primarily achieved by promoting cell division, especially in the apical meristem, leading to elongation and enlargement of pulp cells.
③ Breaking seed dormancy: Dormant grape seeds can be forced to germinate by soaking them in a high concentration (8,000 mg/L) of GA3 for approximately 20 hours.
④ For some wine grape and seedless grape varieties with overly compact clusters, applying 1–5 mg/L GA3 to inflorescences before flowering, or 10–15 mg/L GA3 during flowering, can elongate the rachis and reduce fruit set, thereby achieving cluster loosening.
⑤ Increasing rootstock shoot yield: For grape rootstock varieties with weak growth and short internodes, as well as mother vines used for cutting propagation, repeatedly spraying low-concentration GA3 solution during the growing season can promote vine growth, elongate internodes, increase shoot yield, and improve cutting utilization efficiency.
