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that much water core e;:isted in the fruit before and at harvest in 1956. It 

 has also been sho^m that fruits which have had water core are much more suscep- 

 tible to internal breakdoxm in storage even though much of the water core may 

 disappear. During the 1957-53 season, several storages had Delicious shov7ing 

 considerable amounts of internal breakdoxm in January. In practically all 

 cases where this breakdo^<m occurred, water core v;as also evident. Since there 

 appears to be a close positive correlation between water core and later devel- 

 oping internal breakdo^m, it appears that a reduction in water core would 

 markedly reduce the susceptibility of apples to internal breakdo\^m. 



Uhat is the cause of water core? What factors increase susceptibility? 

 VThat can be done to reduce its prevalence? Studies on water core have been 

 "few and far betxizeen" in the past 25 years. Consequently, ideas on its 

 cause have not been subjected to much recent critical examination or study. 



Water core is somewhat of a misnomer since this trouble often exists in 

 tissues beyond the core. It is generally thought that rapid conversion of 

 starch to sugar in the flesh contributes considerably to the development of 

 water core. The marked increase in sugar in same of the cells supposedly 

 causes water to move into these areas, thus raising the pressure within these 

 cells. Eventually, a leakage of the sugar solution into the intercellular 

 spaces occurs and the water-soaked areas develop. Some observations and 

 studies made in Illinois in 1942, hov/ever, raise some doubts concerning the 

 above explanation. In these studies, it x\7as found that within a water cored 

 apple the soluble solids content of the watex'-cored area was often no higher, 

 if as high, as non-water-cored areas. Also, the v7ater-cored areas appeared 

 to be as high or higher in starch than non-vjater-cored tissues. In view of 

 these findings, it appears that the cause of water core is not fully understood. 



There is considerable agreement concerning factors associated V7ith v^7ater 

 core. Certainly, there is considerable variation in variety susceptibility. 

 Delicious is very susceptible. Many other varieties may develop water core 

 expecially if allowed to become overripe on the tree. Some varieties, such 

 as Delicious, may develop water core before they are overmature as occurred 

 during the 1956 season. VJith most sorts, however, (including Delicious) it 

 tends to get increasingly severe as the fruit ripens. Large fruit is generally 

 more likely to have water core than small fruit although small apples will 

 often have some. Perhaps the reason for this relationship with fruit size is due 

 in part to the fact that large fruits on any given date are usually riper than 

 small ones. For example. Dr. Lord found in 1957 that a midseason irrigation 

 of Mcintosh greatly improved fruit size but accompanying this improved size was 

 hastened fruit ripening and an increase in water core. It would appear that 

 heavy thinning, severe pruning, and a high level of nitrogen fertilization 

 might increase the susceptibility of fruit to v/ater core if these practices 

 increase fruit size and/or the rate of fruit softening. Much has been said 

 about the influence of climatic condition in relation to water core. Past 

 studies of water core indicate that water core is increased by abrupt increases 

 in temperature over the previously prevailing conditions. A heat wave follow- 

 ing a period when 70°F. weather prevailed during the latter part of the grow- 

 ing season may increase susceptibility. However, in 1956 when water core was 

 serious we experienced a growing season that was cooler than average. Certainly, 



