Relationship of Bound Calcium and Inoculum Concentration to the Effect of Postharvest Calcium Treatment on Decay of Apples by Penicillium expansum

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Abstract
Golden Delicious apples were pressure-infiltrated (68.95 kPa) at harvest with 0, 1, 2, or 4% solutions of CaCl2 and stored at 0 C. After 6 mo, the fruits were removed from storage and wound-inoculated with a conidial suspension of 104, 105, or 106 spores of Penicillium expansium per milliliter. After 7 days at 20 C, the fruits were rated for decay severity. The cell walls of similarly treated but uninoculated fruits were extracted and analyzed for Ca concentration. As the Ca concentration of the solutions with which the fruits were infiltrated increased, the amount of cell wall-bound Ca also increased. As the cell wall Ca content increased and the inoculum concentration decreased, the amount of decay decreased. These results indicate that as the inoculum concentration decreases the relative effectiveness of increased cell wall-bound Ca in reducing decay increases.