Effect of Gibberellic Acid (GA3) on Rootstock on the Evolution of the Mandarin Tree Induction "Nadorcott"

Abstract

An application of gibberellic acid (GA3) was applied to different doses (0; 15; 30 ppm) on Nadorcott trees transplanted on five rootstocks (Macrophylla citrus, Carrizo citrange, Troyer citrange, C35 citrange and Swingle citrumelo) during the fruits coloration shifting. A monitoring of the evolution of the floral induction by the counting of leaves and the flowers/ fruits for the sensitive stages: flowering, fruiting and end physiological drop, with physico-chemical analyzes of the leaves at the physiological dropping stage, of caliber during the magnification stage. The shoots on the Swingle Citrumelo rootstock had more flowers than the Citranges and even more than the Macrophylla citrus. This classification is still valid for fruits during fruiting, results of a standard drop for the different rootstocks with the dominance of leaved inflorescence with unique flower. On the other hand, the physiological drop was different from rootstock to the other, more accentuated in Swingle citrumelo, Troyer and Carrizo citrange, and moderate in C35 citrange and Macrophylla citrus. While the GA3 treatment did not significantly affect either the floral induction or the drop in its two phases. It is noted that with the evolution of the flowering there is a significant positive effect of the treatment and of the GA3 dose on the fruits hooking, with a 23% increase for the dose of 30 ppm GA3 compared to the control. However, the variation in size is better for fruits on leaved inflorescence with unique flower, as well as on the Macrophylla citrus rootstock, followed by Citrange (C35 followed by Carrizo and Troyer), and finally Swingle Citrumelo (10% less in comparison with Macrophylla citrus).