Gibberellin (GA3) and Copper Sulfate Pentahydrate (CuSO4·5H2O) Reduce Seeds per Fruit and Increase Fruit Quality in Bac Son Mandarin Fruit

The aim of this study was to find the optimal gibberellic acid (GA3) and copper sulfate (CuSO4·5H2O) concentrations to reduce the number of seeds and increase the quality of Bac Son mandarin fruit. In experiment 1, the control plants (without GA3) were sprayed with water, and the remaining plants were sprayed with different concentrations of GA3 (50, 75, 100, or 125 ppm). In experiment 2, the control plants (without CuSO4·5H2O) were sprayed with water, and the remaining plants were sprayed with different concentrations of CuSO4·5H2O (50, 75, 100, or 125 ppm). Spraying GA3 at 100 ppm in 2018 produced the lowest seed number and the highest theoretical yield. In 2019, spraying GA3 led to a lower seed number and a higher actual yield compared with the control. Similarly, spraying CuSO4·5H2O significantly reduced the number of seeds/fruit and significantly increased the theoretical yield in 2018. In 2019, the total number of seeds/fruit was significantly lower in the CuSO4·5H2O treatments than in the control. Importantly, both GA3 and CuSO4·5H2O treatments did not adversely affect the fruit’s biochemical parameters or yield. These findings demonstrate that spraying GA3 or CuSO4·5H2O at a certain concentration can effectively reduce the number of seeds per fruit in Bac Son mandarin without compromising fruit quality or yield.