The identification of storage disorders, causes and varietal susceptibility
Apples supplied to the market need to be free from internal or external disorders and should have limited potential to develop disorders during the period from retailing to consumption. Growers need to recognise early symptoms of disorders during the monitoring of their stores and to determine the likely progression by examining after a simulated marketing period.
Proper diagnosis of disorders is important in order to take remedial action in the future thereby preventing a recurrence of the problem. Images of the disorders of the flesh and of the skin, described elswhere in this Guide were also included in a wall chart (‘Apple Storage Rots and Disorders’) produced by the HDC and distributed to all registered growers in 2005.
Classification of disorders
Symptom expression varies according to variety and storage conditions but in most cases it is possible to make an accurate diagnosis on the basis of the photographs provided in this section. The disorders have been grouped arbitrarily into those that are visible externally and those that are visible on cutting the fruit. It is accepted that some disorders could be placed in either category e.g. water core develops internally but in some cases, particularly in Bramley apples, the disorder is visible externally.
Within each of the two main categories three further categories of disorders are recognised. Firstly, those that occur as a normal consequence of storage; secondly those induced by the storage conditions and usually due to incorrect concentrations of carbon dioxide and/or oxygen and thirdly, disorders associated with the application of post-harvest chemical treatments (external disorders only) or by mineral deficiencies in the fruit at harvest (internal only).
It is recognised that some disorders could be placed in more than one category e.g. bitter pit and related disorders occur naturally during storage but are induced by mineral deficiencies in the fruit at harvest. Despite this the following classification should be helpful to growers to recognise the disorders and determine the likely cause. The list is not fully comprehensive. Disorders that do not generally affect the more important commercial cultivars in the UK have been omitted.