Fruit canopy position and crop load influence on watercore severity in 'Fuji' apples

Watercore (WC) is a physiological disorder related to carbohydrate metabolism in apple fruit. Late season WC typically develops as 'Fuji' fruit mature on the tree. WC affected fruit develop water-soaked tissue around the vascular bundles and/or fruit core when the intercellular spaces are filled with fluid. While mild symptoms dissipate in storage, severe WC can develop into internal browning with alcoholic off-flavours under controlled atmosphere storage conditions. Fruit position on the tree and crop load are factors associated with WC incidence. In 2015, at the KOB experimental orchard in southwest Germany, late-harvest 'Fuji' apples with a high incidence of WC (93%) were harvested in a single pick from three different positions within the tree canopy (top/middle/bottom) and from trees with two different crop loads (high = full crop but not over cropped or low = ~54% thinned at 67 d before harvest). At-harvest, the fruit weight, fruit density and severity of WC (scale 0 to 5; 0 = no WC to 5 = severe) were determined for all apples per tree. Fruit from low crop load trees showed higher WC compared to high crop load trees. Fruit from the top of high crop load treatment showed a trend to higher WC when compared with fruit from the bottom. Sorbitol was higher in fruit from the low crop load treatment. Comparing the leaf area per fruit with the WC severity suggests, WC development is regulated by other factors in addition to the assimilate supply.