EFFECTS OF THE SUPPLY OF CALCIUM AND MAGNESIUM ON THE COMPOSITION AND SUSCEPTIBILITY OF GOLDEN DELICIOUS APPLES TO PHYSIOLOGICAL AND PATHOLOGICAL DISORDERS

Apple quality is normally defined in terms of the usual commercial standards of colour, size and appearance, storage potential and organoleptic properties. Earlier work on apple mineral nutrition demonstrated the role of potassium, calcium and magnesium in influencing fruit quality and emphasized the special contribution of each cation to several representative characteristics of quality, especially texture, sugar and flavour production.

Optimizing quality by means of suitable techniques for supplying the nutrients to the tree requires an understanding of selective root absorption and the transport processes by which the elements are moved into the tree and distributed to the different organs, especially the fruit. Fertilizer applications must also take into account the complex interaction phenomena which, according to Shear (1975) are generally evidenced in terms of leaf composition. However, this author points out that the supposed antagonistic effect of potassium and magnesium on calcium accumulation in the fruit has not yet been clearly demonstrated.

According to Lewis et al. (1977), who compared the variety Merton Worcester with Cleopatra and Jonathan, different interactions may occur between the mineral element contents of the fruit in these three varieties. Thus there are considerable differences in their susceptibilities to physiological disorders.

Golden Delicious represents 70 per cent of the production of apples in France and we therefore selected trees of this variety to investigate the effects of different rates of supplies of calcium and magnesium on the quality of the crop.