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CONSIDERATIONS IN ATTEMPTING TO IMPROVE ^ 

 THE CALCIUM CONTENT OF APPLES 



2 

 Heather A. Betts and William J. Bramlage 



Department of Plant and Soil Sciences 



Apples are subject to many diseases and physiological dis- 

 orders after harvest, all of which must be controlled to provide 

 a product acceptable to consumers. The mineral nutrient composi 



tion of fruit at harvest greatly influences the occurrence of th 



problems, and it is now widely recognized that calcium (Ca) content 

 is a key factor. Low Ca levels are implicated in development of 

 corking disorders such as bitter pit, cork spot, and Jonathan spot, 

 both before and after harvest. In addition, watercore, internal 

 breakdown, low temperature breakdown, lenticel breakdown, scald, 

 and rot may be intensified when fruit Ca levels are low. From 

 among these problems, bitter pit and internal breakdown have been 

 most extensively studied for their relationship to Ca nutrition. 



Bitter pit has long been recognized as a Ca-def iciency prob- 

 lem. It is influenced by many environmental, orchard management, 

 and storage factors such as water stress, pruning, mineral balance, 

 and time of picking, and many of these influences may actually be 

 acting through modification of fruit Ca levels. Usually, the lar- 

 ger the fruit and the drier the growing season, the more bitter 

 pit is found. Some success in reducing bitter pit has been obtained 

 with calcium chloride (CaCl2) and calcium nitrate (CaCNOj)^ sprays 

 4 to 7 times during the growing season; CaCl2 is usually the pre- 

 ferred material since Ca(N02)2 adds nitrogen to the tree, which can 

 intensify a Ca deficiency. Sprays typically reduce the incidence 

 from 40% to 10% in 'Cox's Orange Pippin' apples in England. Since 

 mobility of Ca in the apple tree is very low, the Ca must be ap- 

 plied directly to the fruit for the treatment to be successful. 

 Ca dips after harvest have also been used to increase the Ca content 

 and decrease bitter pit occurrence during storage. 



Internal breakdown usually occurs after harvest and is often 

 more prevalent in late-picked fruit. High relative humidity in 

 storage accentuates the disorder. It develops as extreme soften- 

 ing of the tissues, with brown discoloration that can become dark- 

 chocolate colored with time, and with the vacular bundles standing 

 out prominently as dark-brown strands. Recent studies show that 

 internal breakdown is greatly influenced by Ca nutrition. In Eng- 

 land, Perring determined that 'Cox's Orange Pippin' apples contain- 

 ing greater than 4.5 mg Ca/100 g fresh weight of flesh will usually 



^This is a review article. Our current suggestions for increasing 



Ca level in apple trees can be found in the May-June, 1977 issue 



of Fruit Notes . 



2 

 Present address: 200 Sullivan Street, Claremont N.H. 03743 



