Effects of gibberellic acid on flowering, fruit quality, and yield of “d'Agen” plums in Mendoza, Argentina

In Mendoza, the primary industrial plum-producing region in Argentina, the ‘d’Agen’ cultivar represents approximately 90% of the cultivated area. The limited implementation of fruit thinning has a detrimental effect on final fruit size. The objective of this study was to determine the timing of flower induction in ’d’Agen’ plum and to evaluate the response to gibberellic acid (GA) application to reduce flower density and improve fruit size. Over three growing seasons in San Rafael (Mendoza), experiments were conducted on plants grafted onto ‘Marianna 2624’, spaced at 5x3 m and drip irrigated. GA (100 ppm) was applied at four distinct phenological stages: fruit set, young fruit, fruit near final size, postharvest, and a control with no GA application. In the first two seasons, the H phenological stage (fruit set, Baggiolini scale) was identified as the optimum time for reducing flowering via GA application. In the third season, increasing GA concentrations (0, 25, 50, 75 and 100 ppm) were evaluated. All concentrations reduced floral density compared to the control. However, fruit set was negatively affected by the 75 and 100 ppm treatments. The decline in flowering (between 60% and 90%) was incompatible with commercial yields. It was concluded that the optimal time for GA application to reduce floral density in ‘d’Agen’ plum was during phenological stage H. Further research is required to determine the most effective dose below 25 ppm. Highlights: • Flower induction in ‘d’Agen’ plum occurs at phenological stage H (fruit set). • Gibberellic acid (GA) application at stage H reduced flower density up to 90%. • High GA concentrations (75-100 ppm) decreased both flowering and fruit set (%). • GA treatments improved fruit size but caused excessive yield reduction. • Doses below 25 ppm should be evaluated to balance fruit size and yield.