ملخص البحث
This work aimed at investigating the role of Ca2+ and Mg2+ compounds or sources on firmness and quality of "Anna" apple fruits whether applied as preharvest or postharvest treatments. Studies on the role of
Mg2+ on these characteristics are rare. Since calcium is immobile nutrient, spray treatment may be less efficient due to the partial deposition and uptake by apple leaves. During 2009 and 2010 seasons, "Anna" apple trees were sprayed ten days before harvest with Ca2+ and, or Mg2+ sources in the form of chloride or sulphate in addition to the control. In the postharvest study, collected apples from untreated trees from the same orchard were dipped in MgCl , CaCl each at 1% or 2% (w/v) alone or in combinations, Ethrel at 100 ppm and (control) 2 2 and then held at room temperature (22±2°C) for 5 days. The preharvest study provided evidence that CaCl2 alone or combined with MgCl resulted in the highest firmness of apple fruits followed by MgSO plus CaSO . 2 4 4 Moreover, the highest values of TSS were found in fruits treated with CaSO alone or combined with MgSO 4 4 when compared with untreated fruits. In addition, CaCl alone or plus MgCl resulted in higher acidity and 2 2 vitamin C than other used treatments. The preharvest applications of various Ca2+ or Mg2+ sources indicated that Ca2+ in the chloride form performed better than Ca2+ in the sulphate form with regard to electrolyte leakage. Meanwhile, the combined form of MgCl plus, CaCl resulted in less leakage as compared with just using MgCl 2 2 2 alone. However, CaCl was still superior to its combination with MgCl in terms of reducing such leakage. 2 2 Carotene content data as another quality attribute of “Anna” apples revealed that apples treated with the sulphate form of Mg2+ had greater carotene content in the skin as compared with those treated with chloride form. The postharvest treatments of various concentrations of CaCl and MgCl (1% or 2% w/v), retarded the 2 2 loss of firmness whether applied individually or in combinations. While Ethrel lead to an adverse effect on flesh firmness in both seasons when compared with the control. Meanwhile, there was no added advantage from increasing the concentration of CaCl or MgCl from 1% to 2% (w/v) with regard to many fruit characteristics 2 2 such as TSS, acidity, chlorophylls a and b and anthocyanin and carotenes in both seasons. It could be concluded that calcium in the chloride form was mostly effective over the sulphate form while the later was better with regard to enhancing carotene formation. Moreover, it is preferred to treat “Anna” apples after harvest with CaCl plus MgCl (1% w/v) and avoid using Ethrel even at low concentration since it accelerates 2 2
all senescence parameters