Effects of various calcium treatments on fruit cracking and cell wall enzyme activities in navel orange

【Objective】 The objective of the study was to find the relationships among calcium contents, cell wall enzyme activities and fruit cracking. 【Method】 Two naval orange (Citrus sinensis) cultivars, ‘Skagg’s Bonanza’ and ‘Newhall’ were treated with exogenous calcium or calcium uptake inhibitor. The contents of calcium, the rate of fruit cracking and the activities of polygalacturonase (PG), cellulase (CX), and pectinmethylesterase （PE） were investigated in different periods.【Result and conclusion】 The contents of calcium in ‘Newhall’ was higher than that in ‘Skagg’s Bonanza’. The content of calcium in the normal fruits was higher than that in cracked fruits in the same cultivar. The mass fraction 2% Ca(OH)₂ treatment increased significantly the calcium content in the pericarp and fruit firmness, reducing the rate of fruit cracking 150 days after anthesis. The mass fraction 2% Ca(OH)₂ treatment reduced the activities of cellulase (CX). Calcium affected the incidence of fruit cracking through its effect on the activities of cell wall enzymes. Its effect was significant in ‘Skagg’s Bonanza’ but not in ‘Newhall’.