Calcium and magnesium gradients in apples with bitter pit

Abstract An electron‐microprobe study of ‘Golden Delicious’ apples with and without bitter pit revealed a 1.7‐fold increase in calcium and a 5‐to 8‐fold increase in magnesium in pitted as compared to non‐pitted tissue. Potassium gradients were not evident in either pitted or non‐pitted tissues. The highest concentration of calcium and magnesium was in the approximate center of the pitted area. No significant gradients in calcium, magnesium and potassium appeared in the control tissue. A scanning electron microscope (SEM) study revealed spherical shaped'globules’ in the pitted tissue only. Electron microprobe analysis indicated these globules to be high in calcium and ultra‐high in magnesium as compared to the surrounding tissue. Golden Delicious apples were vacuum infiltrated with calcium or magnesium alone or in combination with ethylene or ethephon. Within 1 week after infiltration, the magnesium‐treated fruit exhibited bitter‐pit symptoms that were morphologically similar to those induced either by eth...