The redistribution and immobilisation of calcium in apple trees with special reference to bitter pit

Abstract

Abstract In a pot experiment with two year old Golden Delicious apple trees on Merton 793 rootstock it has been shown that calcium was actively absorbed during the shoot extension period as well as during summer and autumn. At dormancy, the bark of the trees contributed about 59% to the total calcium content although it contributed only 12% to the total tree mass. During the period of rapid shoot extension the calcium reserves from the permanent structure of the trees made a very important contribution (22.8%) to the total calcium content of the new growth (shoots, leaves, and fruit), suggesting that at least a portion of calcium present in the trees at dormancy was in an exchangeable form. In another pot experiment with Golden Delicious on Merton 793 rootstock where two levels of spring calcium namely 200 ppm and 2 ppm were superimposed on the same two levels of autumn calcium, it was shown that autumn as well as spring applied calcium was actively absorbed in relation to the supply. Shortly after application, a portion of the autumn absorbed calcium as well as the spring absorbed calcium was not extractable with ammonium chloride, suggesting that this portion was fixed. Accumulation of calcium occurred to a very large extent in the pedicels while only limited amounts reached the fruit. An investigation with the Scanning Electron Microscope and attached EDAX revealed the presence of calcium‐containing crystals in one year old shoots and pedicels. X‐ray diffraction analysis failed to identify these crystals as calcium oxalate. It is suggested that calcium incorporated in these crystals is irreversably fixed. This can at least be one reason why often insufficient quantities of calcium reach the fruit.