RUSSETING AND SHAPE OF GOLDEN DELICIOUS APPLES AS RELATED TO ENDOGENOUS GA CONTENT OF FRUITLETS.

Two kinds of factors have been recognized as interacting in the development of Golden Delicious russet: anatomical factors, i.e. the particular epidermis of Golden Delicious fruit, constituted by a few layers of irregular cells covered by a thin cuticle, frequently cracked, and environmental factors ( rain, high R.H., low temperatures, treatments etc.) (Eccher, 1975).

The incidence of russet is heavier in the valleys, while on the hills russeting decreases at increasing altitudes. The shape of the fruit also differs between high- and lowland grown fruit: elongated the former, round the latter. Histological investigations have shown that the epidermis of the fruit grown on the hills is constituted of layers of cells of regular size, covered by thick cuticle, like that of fruit of cultivars not affected by russet. In such localities even treatments with russet-favouring products do not induce russeting while,in the valley, also spraying pure water may induce it: correlation was found between russeting and net precipitation (Creasy, 1980).

Ga 4+7 treatments reduce russeting and elongate fruit shape and pedicel (Taylor, 1975; Eccher, l.c.,1983; Eccher et al., 1981): the epidermis of treated fruit appears to be more regular, with heavy cuticle similar to that of hill grown apples (Eccher, 1975). On the contrary Paclobutrazol (PP133) treatments increase russeting and shorten fruit shape (Greene et al.1983; Curry et al., 1983;Tukey, 1983).

As it was found that fruitlets from a russet Golden Delicious sport had less GA content than those from standard Golden Delicious ones (Eccher, 1978), it was supposed that there could be a higher gibberellin content in the fruit grown on the hills than in that grown in lowland, at least during the first period of development, but till now this hypothesis was not proved. The aim of this research was to verify this hypothesis by analyzing the Ga-like substances content of fruitlets picked in different orchards at different altitudes.