Exogenous Gibberellins Affect the Setting, Development, and Quality of ‘Golden Delicious’ Apple Fruits

The aim of this study was to investigate the effect of gibberellins on the setting and quality of parthenocarpic apples (Malus × domestica Borkh.). The experiment was conducted in 2021 on the ‘Golden Delicious’ cultivar in the Warsaw University of Life Sciences experimental orchard. During the trial, we compared the effect of various gibberellins, such as GA3, GA4+7, and a mixture of GA3 + GA4+7. These gibberellins were administered to both intact and mechanically injured flowers (damaged by emasculation and style removal) at the pink bud stage. The results clearly demonstrate that gibberellins applied during blooming supported the induction of parthenocarpic fruit setting in Golden Delicious apples; however, fruitlet retention remained significantly lower than in natural pollinated flowers. The most efficient treatment among emasculated flowers was the mixture of GAs, resulting in a final fruit retention of 23.6%. Fruit size and morphology differed across treatments: GA3 applied on intact flowers resulted in the largest parthenocarpic fruits, while the GA4+7 and GAs mixture promoted a more elongated fruit shape. Moreover, gibberellin treatment affected other fruit quality traits. Almost all GA treatments led to a higher soluble solids content in fruits. In addition, apples derived from intact flowers treated with GA3 showed reduced firmness. Overall, our findings indicate that gibberellins can support fruit set, even when flowers are injured, and to lower extent modify fruit quality, but the results depend on flower condi-tions and the type of GA used.