SECONDARY ABSCISSION AND PARTHENOCARPIC FRUIT GROWTH IN APPLE AND PEAR FLOWERS IN VITRO
Abscission in apple could only be induced by auxins and could be antagonized by high concentrations of cytokinins; in pear both auxins and cytokinins were inductive. Auxin-induced abscission in apple always occurred at 2–5 mm from the basal end of the pedicel. In pear the site of abscission was dependent on the concentration of the growth substance. Abscission in both apple and pear pedicels only occurred when pedicels were placed with their basal ends in the media. Abscission increased with increasing temperatures.
Parthenocarpic fruit growth in non-emasculated flowers could not be influenced by growth substances in 'Yellow Transparent', but was strongly increased in 'Lombartscalville'. Parthenocarpic fruit growth in 'Cox's Orange Pippin' and 'Doyenné du Comice' only occurred at 15°C and at a high concentration of GA4+7. Induction of parthenocarpy in fruit growth in 'Cox's Orange Pippin' was possible in flowers of all stages, but in 'Doyenné du Comice' only flowers isolated in the red anther stage were reactive. Addition of only auxins or cytokinins did not influence parthenocarpic fruit growth. In 'Doyenné du Comice' the addition of high concentrations of cytokinins induced the formation of callus-like fruits.