Fruit Cuticle Thickness and Anatomical Changes in Pedicel Xylem Vessels Influence Fruit Transpiration and Calcium Accumulation in Cranberry Fruit

Ca is a key nutrient for fruit quality due to its role in bonding with pectin in the cell wall, providing strength through cell-to-cell adhesion, thus increasing fruit firmness and extending post-harvest life. However, Ca accumulation is mostly limited to the initial stages of fruit development due to anatomical and physiological changes that occur as fruits develop. The objective of this study was to evaluate fruit transpiration, cuticle thickness, and pedicel vessel changes during cranberry fruit development and the effect these parameters might have on Ca translocation. 'Stevens' cranberry fruits were collected weekly, starting seven days after full bloom (DAFB) until 70 DAFB. For each collection date, fruit transpiration was evaluated in the field, and samples were taken to analyze total fruit Ca content, stomata density, cuticle thickness, pedicel anatomical changes, and xylem functionality. Ca accumulation in the fruit exhibited a sigmoidal curve, beginning at 0.04 mg per berry at 7 DAFB, increasing to a maximum of 0.1 mg per berry at 28 DAFB, and remaining constant until harvest (70 DAFB). Fruit Ca accumulation was mostly explained by fruit transpiration, which exhibited a similar sigmoidal pattern. The rapid decline in fruit transpiration was largely modulated by increases in cuticle thickness, as well as anatomical changes in the pedicel xylem, thereby reducing the capacity to transport water and nutrients into the fruit. Thus, this research could help cranberry growers maximize fruit Ca content by prioritizing fertilization during the early stages of fruit development.