Calcium ions decrease water-soaking in strawberries

Water soaking is a common disorder of field-grown strawberries (Fragaria × ananassa Duch.). It develops when ripe fruit is exposed to rain. Here we investigate the effects of Ca on water soaking. Fruit was incubated in solutions of various Ca salts and the extent of water soaking quantified using a simple rating scheme. Exposure to CaCl(2) (10 mM) decreased water soaking and anthocyanin leakage but had no effect on water uptake. The decrease in water soaking due to CaCl(2) was not limited to a single cultivar but occurred in all cultivars examined. Incubating fruit in a chelating agent (EGTA) increased water soaking compared to the water control. Calcium salts of different acids varied in their effects on water soaking. Only CaCl(2) reduced water soaking significantly. The chlorides of different cations, also varied in their effects on water soaking. Those of the monovalent cations had no effects on water soaking, while those of the divalent cations (CaCl(2), BaCl(2) and SrCl(2)) and of the trivalent cations (FeCl(3) and AlCl(3)) were all effective in decreasing water soaking. Overall, CaCl(2) decreased microcracking of the strawberry cuticle as compared to deionized water. Furthermore, CaCl(2) also reduced the leakage of anthocyanins from flesh discs, irrespective of the osmotic potential of the incubation solution. Our results indicate that CaCl(2) reduced water soaking by decreasing cuticular microcracking, by decreasing leakage of plasma membranes and, possibly, by increasing the crosslinking of cell wall constituents.