Submitted to: American Society for Horticultural Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 13, 1998
Publication Date: N/A
Interpretive Summary: A major thrust of postharvest research is to reduce the use of fungicides in controlling decay and losses of fruit during storage. Previous research has shown that postharvest calcium maintains fruit firmness and reduces decay due to fungal pathogens. However, the beneficial concentration range and optimal concentration of calcium to apply to fruit had not been established. Current research established that a 3 percent calcium solution as its chloride salt was the maximum calcium salt concentration that can be applied to 'Golden Delicious' apples without injuring the fruit. A 2 percent calcium chloride treatment is recommended since this concentration significantly extends postharvest life and fruit resistance to postharvest decay while allowing for salt buildup that occurs in apples during cold storage. This information provides apple growers and packinghouse operators with a guide for maintaining the quality of apple fruit in storage while reducing their dependence on postharvest use of synthetic fungicides.
Technical Abstract: Changes in tissue water relations, cell wall Ca levels and physical properties of Ca-treated and untreated 'Golden Delicious' apple fruit (Malus domestica Borkh.) were monitored for up to 8 months after harvest. Pressure infiltration of fruit with CaCl2 solutions at concentrations up to o50 g/liter reduced both fruit softening and air space volume of fruit in a concentration-dependent manner. Fruit that were pressure infiltrated with CaCl2 solutions between 20 and 30 g/liter and then waxed to reduce water loss during storage showed no peel injury. At Ca concentrations up to 30 g/liter, cell wall bound Ca approached saturation whereas soluble Ca showed a linear dependence. At higher external Ca concentrations, only soluble Ca in the tissue increased. During 8 months of cold storage, cell wall Ca-binding capacity increased up to 48 percent. The osmotic potential lof apples harvested over three seasons ranged between -1.32 and -2.23 MPa. In CaCl2 solutions up to 50 g/liter, turgor potential was > 0.6 MPa in tissue disks incubated in 20 or 25 g/liter solutions of CaCl2 and was more than 3 times higher than in tissues incubated in low (< 5 g/liter) or high ( > 40 g/liter) concentrations of CaCl2. At osmotically equivalent concentrations, turgor potential was up to 40 percent higher in Ca-treated than in sorbitol-treated tissue. The results suggest that postharvest treatment with 20 to 30 g/liter solutions of CaCl2 are best for maintaining fruit water relations and storage life of 'Golden Delicious' apple fruit while minimizing the risk of salt-related injuries to fruit. While higher concentrations of CaCl2 may better maintain firmness, these treatments adversely affect fruit water relations & increase the risk of fruit injury.