The when and where of calcium uptake

Calcium is a xylem mobile mineral, and as fruit xylem connections and pathways are thought to be reduced during maturation, early accumulation is vital. Calcium has been implicated in building resilience to cracking into fruit, with many studies exploring the impact of late season calcium chloride spray applications on cracking. These trials have produced inconsistent results but early and repeated spray patterns for calcium uptake are supported by studies in apples. Enhanced calcium uptake rates have been recorded in the sweet cherry variety ‘Van’ with the use of thickeners and surfactants. The stylar end of cherry fruit has been identified as the preferential site of calcium uptake in variety ‘Bing’. Recent studies have shown that stomata play a greater role in nutrient uptake than previously thought, but still only about 10% of leaf stomata are involved. A major limitation of using direct calcium application to prevent cracking is the unsightly residue left on the fruit, therefore the benefits must outweigh this disadvantage. To assess from where calcium was incorporated into fruit (vascular supply, or directly across the leaf or fruit skin) a trial was undertaken in Southern Tasmania, Australia which included calcium applications supplied via fertigation and/or foliar spray applications. Foliar sprays commenced either before or after Stage II of fruit development to assess when any uptake occurred. Calcium levels were assessed using ICP-MS at both Stage II and at harvest maturity. Relationships between fruit calcium and fruit quality (firmness) were explored, and the potential for continued use of calcium in mediating fruit cracking after rainfall discussed.