DIFFERENTIAL EFFECT OF CALCIUM AND STRONTIUM ON FLESH FIRMNESS AND PROPERTIES OF CELL-WALLS IN APPLES

Apples of cv. Golden Delicious, about one and a half months after frui t set, were sprayed eight times at weekly intervals with 40 mM solutio n of CaCl2 and SrCl2. The firmness of the fruits, beta-D-galactosidase activity, contents of free and covalently bound pectins, and hemicell uloses were not significantly different under various treatments at th e time of harvest. However, after 20 d of storage, the flesh firmness, contents of total, ionically and covalently bound pectins with respec t to control were higher in CaCl2 and lower in SrCl2 treated fruits. T he activity of beta-D-galactosidase was decreased by CaCl2 but not by SrCl2 treatment. The total pectin content of the walls with respect to control was higher in CaCl2 and lower in SrCl2 treated apples. It was observed that preharvest application of CaCl2 may not always lead to firmer fruits at the time of harvest but may result in a better retent ion of firmness during storage. It was further indicated that the effe ct of calcium on flesh firmness and cell wall properties was not simpl y electrostatic or of a bivalent cation but through some specific effe ct.