Occurrence and importance
Internal browning is a low-temperature storage disease of certain apple varieties. It is decidedly regional in its occurrence. Internal browning is particularly serious in Yellow Newtown apples grown in the Pajaro Valley in California, and it occurs also in Yellow Bellflower and other varieties grown in that section, where the weather is cool and cloudy or foggy through the growing season. It is occasionally found in Yellow Newtown grown in other states, notably Washington, Oregon, and New York, and in Rhode Island Greening grown in New York. Traces of the disease have been found in Yellow Newtown grown in Virginia, but ordinarily conditions there do not favor development of the disorder.
Symptoms
Internal browning develops only in fruits that have been stored at 31° to 32 °F for some time. Symptoms of internal browning can not be observed unless the fruit is cut. A cross section of a diseased apple typically shows affected tissues to be brown and firm and usually radiating out from the core area (top photo). Occasionally, the internal browning may be confined only to the core area. Less frequently, the core area may be normal and browning present in the outer fleshy tissues. The firmness of the diseased tissues, however, readily separates internal browning from the other internal physiological disorders.
Causal factors
The predisposition of apples to internal browning is related to cool temperatures and lack of sunshine during the growing season. Such weather conditions frequently prevail in the Pajaro Valley, which is located in California's coastal fog belt. Late harvest or delayed storage of susceptible varieties increases incidence of internal browning. Cold storage temperatures in the range of 31° to 32 °F are particularly favorable to development of internal browning. The browning increases with length of storage season and after withdrawal from storage.
Control measures
Prompt storage of apples at 38° to 40 °F will control internal browning. To prevent loss of storage life at these temperatures, controlled-atmosphere storage should be used for those varieties that are sensitive to storage at 31° to 32 °F.
