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 o f 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 d egrees 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 o nes; However, after three weeks of Storage, both average and small fru its were showing better retention of firmness by CaCl2 treatment. Thus , preharvest treatment of CaCl2 may not necessarily always lead to fir mer fruits at the time of harvest but may result in better retention o f firmness during storage. The results are discussed in relation to ce ll-wall yield, beta-D-galactosidase activity, total, free, ionically a ssociated and covalently bound pectins, and hemicellulose contents. Th e differences in behaviour of average and small fruits to calcium appl ication seem to be associated with the calcium content of covalently b ound pectin fraction of the walls.