EFFECT OF POSTHARVEST CALCIUM-CHLORIDE TREATMENTS ON TISSUE WATER RELATIONS, CELL-WALL CALCIUM LEVELS AND POSTHARVEST LIFE OF GOLDEN DELICIOUS APPLES

Changes in tissue water relations, cell wall calcium (Ca) levels and p hysical properties of Ca-treated and untreated 'Golden Delicious' appl es (Malus xdomestica Borkh,) were monitored for up to 8 months after h arvest. Pressure infiltration of fruit with CaCl2 solutions at concent rations up to 0.34 mol.L-1 reduced both fruit softening and air space volume of fruit in a concentration-dependent manner. Turgor potential- related stress within the fruit persisted during storage and was highe r in Ca-treated than in untreated fruit. Fruit that were pressure infi ltrated with CaCI2 solutions between 0.14 and 0.20 mol.l(-1) and then waxed to reduce water loss during storage showed no peel injury. Calci um efflux patterns from apple tissue disks indicated two distinct Ca c ompartments having efflux kinetics consistent with those for cell wall Donnan-phase bound and water free space soluble Ca. At Ca concentrati ons up to 0.20 mol.L-1, cell wall bound Ca approached saturation where as soluble Ca showed a linear dependence. At higher external Ca concen trations, only soluble Ca in the tissue increased. During 8 months of cold storage, cell wall Ca-binding capacity increased up to 48%. The o smotic potential of apples harvested over three seasons ranged between -1.32 and -2.33 MPa. In tissue disks, turgor potential changes caused by adjusting the osmolality of the incubation solution with CaCl2 or sorbitol were accompanied by changes in the osmotic and water potentia ls of the tissue. In CaCl2 solutions up to 0.34 mol.(-1), turgor poten tial was greater than or equal to 0.6 MPa in tissue incubated in 0.14 or 0.17 mol.L-1 solutions of CaCl2 and was more than 3 times higher th an in tissues incubated in low (less than or equal to 0.03 mol.L-1) or high (20.27 mol.L-1) concentrations of CaCl2, At osmotically equivale nt concentrations, turgor potential was up to 40 %higher in Ca- than i n sorbitol-treated tissue. The results suggest that postharvest treatm ent with 0.14 to 0.20 mol.L-1 solutions of CaCl-1 are best for maintai ning fruit water relations and storage life of (Golden Delicious apple s while minimizing the risk of salt-related injuries to the fruit. Whi le higher concentrations of CaCl2 may better maintain firmness, these treatments adversely affect fruit water relations and increase the ris k of fruit injury.