Abstract text: Physiological fruit drop can limit yield in persimmon (Diospyros kaki L.) cv. ‘Rojo Brillante’, particularly during the second drop period, which is strongly influenced by environmental stress and varies between seasons. Calcium is considered a key regulator of cell wall stability and may influence fruit retention through its role in abscission zone integrity. This study evaluated whether calcium supply affects fruit abscission, tissue nutrient distribution, and calcium localization patterns.

Three treatments were compared in a commercial orchard: untreated control, foliar calcium, and soil calcium, applied four times from pre-fruit set to early fruit development. Both calcium treatments significantly reduced fruit drop compared to the control. Cryo-SEM observations revealed calcium crystals exclusively in the calyx part of the fruit, corresponding to the abscission zone, with no treatment differences in this region two months after the second application. However, nutrient analysis showed that calcium treatments increased calcium in the stylar part: soil applications enhanced calcium percentage, while foliar treatments increased absolute calcium content relative to the control.

These results indicate that although structural calcium accumulates locally in the abscission region, calcium supply can still enhance soluble fraction in distal tissues, potentially contributing to improved cell wall stability and fruit retention.