Some varieties of apples under certain conditions show a peculiar glassiness in and about the core. The Fall Pippin is said to be badly affected, and the disease has been observed on several other varieties, including the Early Harvest, Yellow Transparent, Pound Sweet, Tompkins King and Rambo. In general, summer varieties suffer most.
Water Core has undoubtedly been present in the apple sections of the world for many years, but authoritative records are not old. It was noted in Maryland in 1908, but is thought to have occurred there several years before. Reports have recently come from other regions of the United States which make it certain that the trouble occurs generally over the country, particularly in arid and semi-arid districts. Apple - growers of Europe, Asia, Africa and Australia are familiar with this peculiar disease in the fruit, and the complaints which come from these continents indicate its troublesome nature.
Affected fruits are found more particularly on the tops of thrifty trees, and on healthy branches which have less foliage as a result of having been pruned back. Shaded fruits may be expected to be affected very little in comparison to those which are exposed to the sun. The diseased portion of the fruit is not easy to detect externally, hence the presence of Water Core in an apple may not be suspected. However, the experienced observer is sometimes able to detect diseased fruits by their external appearance. Fruits which should be normally green or yellow will show a blush on one side. Red or dark-colored apples do not exhibit such marked external signs of the trouble. On cutting into a Water Cored apple, hard, transparent, watery areas are found in the flesh. Such areas are practically always in close connection with the vascular system. The first evidences of Water Core are found here. The bundle shows a water-soaked area about it. The lesion may be near the stem or elsewhere in the flesh, since the bundles are scattered. Occasionally these scattered spots may be small, or there may be extensive watery areas near the surface of the fruit, although none extends up to the skin. Affected apples give off a sweetish, fermented odor, and the taste is not unlike that of frozen fruit. In the later stages, liquid is usually found in the seed cavities and the harder inner membrane of the carpels is cracked and covered with hair - like growths, which eventually assume a brownish aspect.
The presence of excess water in the affected tissues gives the described appearance. But the factors which bring about this excess water in certain regions of the fruit are not thoroughly understood. It seems certain that fungi, bacteria and insects are not concerned in bringing about Water Core. It is generally accepted that conditions affecting transpiration are the prime factors inducing Water Core. Reduced transpiration results usually in excessive sap-pressure, and water is forced into the spaces between the cells of the fruit, giving the affected area a glassy, transparent appearance. There is no one factor which can bring about Water Core; two or more factors are necessary, and these must favor excessive sap-pressure and reduced transpiration. The abnormally high sap-pressure, of course, comes only when there is a continuous flow of sap, and is usually accompanied by'lessened transpiration. Observations strongly indicate that the more prominent factors inducing Water Core are as follows: - (1) Vigor in trees. Excessive growth, especially in young trees just coming into bearing, is favorable. Such trees do not ordinarily bear a heavy crop, but set only a few, abnormally large apples. It has also been noticed that fruits borne near the tips of branches in trees of any age are susceptible to Water Core, provided such trees are growing rapidly. On the other hand, trees making a poor growth rarely show glassy fruits. If vigor or unusual vegetative growth be a factor concerned in Water Core, then such factors as promote this condition are, in turn, contributing causal factors. High cultivation should be mentioned in this connection. While excessive cultivation alone cannot be held responsible for this disease, it is nevertheless an important factor. (2) Excessive water-supply. Rain or water of irrigation under certain conditions is highly important. If a superabundance of water comes just before maturity of the fruit, and if this excess be accompanied by extremes of temperature and atmospheric humidity, the disease is very likely to appear. Suppose, for example, following a heavy rain-fall the sun warms the soil to such an extent that considerable water is taken up rapidly by the roots. As long as the sun shines the water will be given off by transpiration; but at night the temperature of the air is lowered markedly while that of the soil is not appreciably changed. Thus the roots continue to send water rapidly to the aerial parts, but under the cool atmospheric conditions transpiration is decidedly checked. As a result, the water accumulates in the fruits and there is developed an abnormally high pressure. Finally the water is forced into the intercellular spaces. Other organs do not show signs of this disease; the fruits suffer on account of their inability to offer resistance to this abnormal pressure. Those fruits which occupy terminal portions on the branches suffer most because they are exposed to extremes of temperature. Likewise apples on the south or southwest sides of trees are always most affected. (3) Defoliation or reduced foliage-area. Should a tree be defoliated by some pathogene or other cause shortly before the ripening-period, the fruit is likely to suffer from Water Core. The decrease in the foliage-area results in reduction of the evaporating surface, consequently an excess of water is liable to accumulate. Severe pruning may also act detrimentally in this way. The removal of a large number of branches means the reduction in the number of leaves, and therefore checked transpiration. Any injury to the foliage, but which at the same time does not cause defoliation, tends to have the same effect with respect to Water Core. (4) Excess tension set up in the cell as a result of a rapid ripening process. In ripening, the starch is converted into sugar; water is absorbed by the sugar and there results a high pressure tending to force water into the intercellular spaces.
It seems to be out of the question to wholly prevent Water Core, since certain climatological factors are so intimately involved. Some authorities say that it is absent where the soil is well managed throughout the year; that it is absent in soil of a loose texture; and that adequately drained soil seldom produces glassiness in fruit. Further observations along these lines are necessary before positive conclusions can be reached. The conditions already enumerated under which Water Core has been observed may offer some suggestions as to remedial measures, although prevention or cure are as yet little short of impossible. Among those recommendations worthy of note are: - (1) In thinning the crop those fruits nearest the tip of the branches should be removed, especially in cases where preference is not otherwise to be shown. (2) Cultivation should proceed normally, and a cover - crop should be planted at least as early "as the middle of July to remove excess moisture.
(3) Since a well - drained orchard may be expected to suffer less than one poorly drained, proper drainage should be provided.
(4) Where irrigation is practiced, the water should be supplied in reasonable quantities; particular care is essential if irrigation is practiced at or just prior to the ripening-period. (5) If the climate in the region concerned is peculiarly subject to great range in temperature and relative humidity, the above measures should be more rigidly adhered to than where the climate is quite the opposite. (6) The orchard should be sprayed to keep the foliage in good condition; this practice has value in the control of Water Core in that the leaves, which are the organs of transpiration, are better able to function. (7) Pruning should not be done just before the fruit ripens, for such an operation lessens the amount of foliage, thus favoring the development of Water Core. (8) Fruit should be picked in proper season; it should not be allowed to hang on the tree after it is ready to pick, since this tends to increase the severity of the disease. (9) As soon as the fruit is picked it should go into storage. Under proper conditions of storage affected fruit, unless seriously injured, will entirely recover. The storage should be cool (not cold storage), and of even temperature.
Norton, J. B. S. Water core of apple. Phytopath. 1:126 - 128.
1911. Clinton, G. P. Report of the botanist. Water core. Connecticut Agr. Exp. Sta. Rept. 1913: 8 - 9. 1914. O'Gara, P. J. Studies on the water core of apple. Phytopath. 3:
121 - 128. 1913. Cobb, N. A. Water core in apples. New South Wales Agr. Gaz. 2:
286 - 287. 1891. Campbell, A. G. Constitutional diseases of fruit trees. Victoria Agr.
Dept. Journ. 3: 463 - 465. 1905. O'Gara, P. J. Water core of apple. Office of Pathologist and Local U. S. Weather Bur. Sta., Medford, Oregon, Bul. 9: (not paged).