Abstract text: Fruit firmness is a key quality attribute related to cell wall integrity, yet it is typically assessed as a single average value that overlooks internal spatial heterogeneity. Despite its relevance in fruits such as persimmon, the physiological basis of firmness gradients remains poorly understood. This study provides the first characterization of firmness differences between the upper (calyx) and lower (stylar) fruit parts of ‘Rojo Brillante’ persimmon and examines their relationship with spatial mineral distribution and nutrient balance. Fruit representative within-canopy and field variability were analysed at harvest and after 30 days of simulated commercialization.

Firmness and mineral gradients were detected: the upper part showed higher firmness and greater Ca, Mg, Mn and Fe concentrations, whereas the lower part accumulated more P, K and S. Firmness values were correlated between regions, being at harvest the lower part which emerged as a mechanical weak point. After storage, the upper region exhibited greater variability, and its firmness was inversely associated with Mg concentration. Moreover, larger intra-fruit firmness differences were linked to greater asymmetry in the Mg/Ca ratio. These findings indicate that mineral-driven heterogeneity underlies internal firmness patterns, suggesting that optimizing Ca–Mg balance during fruit development could improve postharvest performance.