- 3 



peel has al-out 3 times more Ca in it than has the flesh. Because 

 of this uneven distribution, Ca concentration is sometimes extreme- 

 ly low in the fruit tissues most sensitive to physiological disor- 

 ders. 



An understanding of these characteristics of Ca nutrition of 

 apples is important in designing a program to improve fruit Ca lev- 

 els. Much work has been done worldwide to increase Ca levels in 

 apples. Soil treatments have been of little measureable benefit. 

 Tree sprays of Ca salts such as CaCl2 and Ca(N07)2 have given some 

 success in increasing Ca levels and reducing disorders. Their ef- 

 fectiveness usually increases with concentration of the salts in 

 the spray mix and with the frequency of spraying, A common cause 

 for unsatisfactory results is poor spray coverage; because of the 

 low mobility of Ca to fruit within the tree, thorough and uniform 

 coverage is essential. This problem may be intensified by appli- 

 cation of Ca in concentrate sprays. 



Postharvest dips have the advantage of being able to complete- 

 ly cover the fruit with solution. In England, researchers in one 

 trial got similar control of bitter pit with a postharvest immer- 

 sion for 1 minute in 0.05 M Ca(N03)2 as with 4 summer sprays of the 

 same solution. However, CaCl^ again is considered to be a more 

 effective salt for dips than CaCNO)-, at least in part because 

 CafNOj)^ will support bacterial growth and leave an undesirable 

 residue on fruit after storage. Other substances have been added 

 to the dipping solution in order to increase the penetration of 

 Ca into the fruit, with varying and often conflicting results. 

 The most striking effects have been obtained by adding "thickeners" 

 to the dipping solution. Mason and his colleagues in Canada have 

 used arrowroot flour and the commercial thickener keltrol with 

 great success. With 'Mcintosh,' dips in 41 CaCl2 plus keltrol al- 

 most tripled flesh Ca during storage, and significantly reduced 

 the softening rate of the fruit during and following storage. These 

 thickeners apparently cause much more Ca to adhere to the surface 

 of the apple, from which it can be absorbed into the flesh later 

 during storage. 



Injury can result from excessively heavy treatments to in- 

 crease Ca levels. Tree sprays can severely injure leaves, especi- 

 ally early in the season or in hot weather. Postharvest dips can 

 cause injury to the surface of the fruits, usually appearing as a 

 burn or as black spots at the calyx end of the fruits. In most 

 cases, fruit inury is not serious, but in a report from New Zea- 

 land 23% of 'Cox's Orange Pippin' were injured by a 2.5% CaCl2 dip. 



As we learn more about the effects of mineral deficiencies on 

 storage life and quality retention in fruit, it becomes increasingly 

 important to develop strategies to overcome the deficiencies. Solu- 

 tions will not be simple. Following a comprehensive study of fac- 

 tors related to storage breakdown of 'Spartan' apples in British 



