Calcium application and impacts on cherry fruit quality

The most common mineral employed in the management of fruit cracking is calcium (Ca). Ca is a xylem mobile mineral, and as fruit xylem connections and pathways are thought to be reduced during maturation, so early accumulation is vital. Ca has been implicated in building resilience to cracking into fruit, with many studies exploring the impact of late season calcium chloride (CaCl₂) 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 Ca uptake rates have been recorded in the sweet cherry cultivar 'Van' with the use of thickeners and surfactants. A major limitation of using direct Ca application to prevent cracking is the unsightly residue left on the fruit, therefore the benefits must outweigh this disadvantage. To assess from where Ca was incorporated into fruit (vascular supply, or directly across the fruit skin) trials were undertaken in southern Tasmania, Australia which included Ca applications supplied via fertigation and/or foliar spray applications. Foliar sprays commenced either before or after Stage II (pit-hardening) of fruit development to assess when any uptake occurred. Ca levels were assessed using ICP-MS at both Stage II and at harvest maturity. It was expected that increased calcium would strengthen fruit tissue and reduce cracking resulting from rain. Relationships between fruit Ca and fruit quality (firmness) were explored, and the potential for continued use of Ca in mediating fruit cracking after rainfall discussed.