EFFECT OF PREHARVEST APPLICATION OF CALCIUM ON FLESH FIRMNESS AND CELL-WALL COMPOSITION OF APPLES - INFLUENCE OF FRUIT SIZE

Apples, cv. Golden Delicious were subjected to ten preharvest sprays of 1.2% CaCl2 at weekly intervals. At the beginning of the climacteric stage, the fruits were harvested and sorted to small (4-5 cm dia.) and average (6-7.5 cm dia.) sizes, and stored at ambient conditions (25 degrees C). The firmness of small fruits was higher than average ones. Application of CaCl2 resulted in higher flesh firmness at the time of harvest in average fruits but showed no significant changes in small ones; However, after three weeks of Storage, both average and small fruits were showing better retention of firmness by CaCl2 treatment. Thus, preharvest treatment of CaCl2 may not necessarily always lead to firmer fruits at the time of harvest but may result in better retention of firmness during storage. The results are discussed in relation to cell-wall yield, beta-D-galactosidase activity, total, free, ionically associated and covalently bound pectins, and hemicellulose contents. The differences in behaviour of average and small fruits to calcium application seem to be associated with the calcium content of covalently bound pectin fraction of the walls.