Mechanisms Regulating Apple Cultivar Susceptibility to Bitter Pit
Fruit susceptibility to Ca2+ deficiency disorders has been associated cellular localization of Ca2+ and Ca2+ interactions with other nutrients. This study aimed to better understand the mechanisms regulatingbitter pit (BP) development by comparing nutrient content and cell wall Ca2+ binding capacity in ‘Fuji’and ‘Granny Smith’ (GS) apples. After two months of storage at 0◦C, ‘Fuji’ apples had no BP, while GS appleshad 52.5% BP incidence. Non-pitted GS fruit had higher flesh and skin Ca2+ concentrations than pitted GSfruit, the latter having similar flesh and skin Ca2+concentrations to ‘Fuji’ fruit. Although ‘Fuji’ apples hadthe highest cell wall Ca2+ concentration, most of the Ca2+ shifted from the water-insoluble pectin into thewater-soluble pectin fraction during storage. In GS, there was a large increase in the Ca2+concentrationin water-insoluble pectin during storage and a small increase in Ca2+ content in the water-soluble pectin. Pitted GS fruit had higher malic acid content, as well as higher [(K++Mg2+)]/Ca2+ and N/Ca2+ratios inflesh and skin tissues than non-pitted GS and ‘Fuji’ fruit. The results indicate that apple susceptibility toBP can be enhanced by increasing water-insoluble pectin Ca2+, as well as [(K+ +Mg22+)]/Ca2+and N/Ca2+ratios in the fruit.