INFLUENCE OF SHOOT GROWTH, AVERAGE FRUIT WEIGHT AND DAMINOZIDE ON BITTER PIT

Considerable information is now available relating the mineral composition of apple fruits to their physiological behaviour. Garman and Mathis (1956) showed that fruits with a high Mg/Ca ratio are more susceptible to bitter pit and that application of calcium during the growing period markedly reduces this disorder. The results in most publications are based on random sampling of fruits and leaves from all parts of the tree but Preuschoff (1968) showed that the mineral composition of individual leaves varied according to the age and position of the shoot within the tree (topophysis). Stoll (1973) has demonstrated that the incidence of physiological disorders in apples varies according to its exposure to the sun and the age and type of fruit spur. These differences suggested that variations might also be found in the mineral composition of fruits from different parts of the tree and trials were therefore undertaken in 1972–1975 to investigate this aspect. The work was also extended to evaluate the effects of changes in shoot growth, resulting from different pruning systems and treatments with daminozide, on the mineral content of fruits and their susceptibility to bitter pit.