Effect of preharvest application of calcium on the postharvest physiology of apricot fruit

The effect of preharvest calcium (Ca) foliar application on ethylene (C2H4) production, respiratory rate, soluble polyuronides, and fruit firmness of 'Bebekou' apricot fruits was determined. The study was carried out in two experimental years, 1991 and 1992. Calcium was applied 21, 17, and 13 days before harvest for 1991 at the concentration of 0.5% calcium chloride (CaCl2) each time and 16 and 12 days before harvest for 1992 at the concentrations of 0.8 and 0.7% CaCl2, respectively. Calcium treatment resulted in a 30-76% increase in the Ca content of fruit flesh. Treated fruits had significantly lower C2H4 production rates than control during (i) four (1991) or five days (1992) at 21 degrees C out of the 7-day period examined immediately after harvest, and (ii) one (1991) or two days (1992) at 21 degrees C out of the seven-day period examined immediately after a 3rd- (1991) or 4th-week (1992) storage period at 0 degrees C. After harvest, Ca-treated fruits displayed one day delay to reach the peak rate of C2H4 production. Respiratory rate was significantly suppressed over a five-day period at 21 degrees C out of the seven-day period examined immediately after harvesting. However, after four weeks of storage at 0 degrees C, there was not any significant effect of Ca on the respiratory rate. The respiratory peak rate occurred earlier in the control fruits compared to that of the Ca-treated fruits at harvest time. Calcium-treated fruits were about 70% firmer than the untreated ones at harvest time. Furthermore, this difference persisted after four weeks of storage at 0 degrees C. Foliar-applied Ca produced a 29% decrease in the soluble polyuronide content of the fruits at harvest time, but not after four weeks of storage. Fruit firmness was positively correlated to the Ca content of fruits while the soluble polyuronide content of the fruit was negatively correlated to fruit Ca.