ORCHARD FACTORS AFFECTING FRUIT STORAGE QUALITY AND PREDICTION OF HARVEST DATE OF APPLES

Abstract

Numerous and well-recognised factors may affect the quality of pome fruits at harvest and following storage. Generally, fruit quality is associated with climatic and soil conditions, tree characteristics and cultural practices. The apple fruit is especially sensitive to low calcium concentration and susceptible to a number of physiological disorders during storage. Many environmental and cultural factors influence calcium content of apple fruits at maturity. When dormancy has been broken and bloom period begins, many important factors come into play that can affect ultimate fruit quality. These are related to fertilisation, pollination, seed number and fruit set. Number of seeds may influence the rate of calcium transport to the apples, probably by production and transport of auxins. On the other hand. fruits, which develop from terminal flowers, are richer in calcium than those developing from lateral ones. The location of fruits in the tree crown is also influencing calcium concentration, and incidence of physiological disorders; more fruits are affected in the upper parts of canopy. This is probably due to a poorer calcium input to these fruits. Cropping level of the tree is also a factor. Fruits from trees with light crops show generally a lower calcium concentration and they are more prone to bitter pit and internal breakdown. It seems that fruits compete in some manner with vegetative tissues for calcium transported from the root system. Summer pruning can have a strong positive effect on fruit quality, which at least in part is associated with increased Ca levels. Calcium treatments have also been shown to reduce the occurrence of physiological disorders. Wide variability of individual fruits within a tree as well as of trees within an orchard block, in respect to fruit maturation and subsequent storability was found to be associated with fruit calcium levels and differences in bloom time. Apples low in calcium show an earlier onset of the endogenous ethylene climacteric as fruits mature on the tree. On the other hand, fruits developed from late blooming flowers were considerably smaller than those from early blooming ones. Fruits from late blooming flowers produced less ethylene, exhibited a lower starch index and developed superficial scald during storage. This indicates that apple cultivars with a prolonged bloom period should be harvested at least twice. The date of harvest plays an important role in the quality of stored apple Ethylene is regarded as a more reliable indicator of physiological maturity than starch hydrolysis. In addition to this information, we attempted to predict the onset of the ethylene climacteric. The rapidity of the development of the ethylene climacteric is related to fruit maturity and we used this developmental phenomenon to predict the optimal harvest date.