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The application of gibberellic acid (GA3) at any time from early November until bud sprouting, resulted in a significant inhibition of flowering, in the sweet orange [C. sinensis (L.) Osbeck] and the Satsuma (C. unshiu Marc.) and Clementine (C. reticulata Blanco) mandarins. Two response peaks were evident: the first occurred when the application was timed to the translocation of an unknown flowering signal from the leaves to the buds. The second occurred during bud sprouting, at the time the flower primordia were differentiating. From the pattern of flowering, it appears that the mechanism of inhibition was similar irrespective of the timing of GA3 application. There was an initial reduction in bud sprouting affecting selectively those buds originating leafless inflorescences. An additional inhibition resulted in a reduction in the number of leafy inflorescences with an increase in the number of vegetative shoots, suggesting the reversion of a floral to a vegetative apex. The inhibited buds sprouted readily in vitro but invariably vegetative shoots were formed. A continuous influence of the sustaining branch is necessary to keep the flowering commitment of the buds; irreversible commitment occurs when the petal primordia are well differentiated. [ABSTRACT FROM AUTHOR]

The flowering response of Owari Satsuma mandarin (Citrus unshiu Marc) to low temperature treatments has been determined using potted trees and in vitro bud cultures. In potted trees the chilling treatments released bud dormancy and enhanced both sprouting and flowering, but these two responses could not be separated. However, bud cultures showed no dormancy, and a specific effect of low temperature on flower induction was demonstrated. Low temperature appears to have a dual effect, releasing bud dormancy and inducing flowering. Potential flower buds have a deeper dormancy than vegetative buds, and the first stages of flower initiation seem to occur before the winter rest period.

Natural and post‐harvest ethylene‐induced pigment changes in the rind of Satsuma mandarin (Citrus unshiu Marc.) fruits respond differently to the exogenous application of growth regulators. Both gibberellin A3 and the synthetic cytokinins N6‐benzyladenine and kinetin opposed the ethylene‐induced chlorophyll destruction, while the loss of chlorophyll during natural maturation was retarded by the gibberellin but not by the cytokinins. This different behaviour suggests that ethylene may not be playing a central role in the endogenous control of ripening. Carotenoid accumulation during natural maturation is apparently controlled through a different mechanism than chlorophyll loss since it is reduced both by the cytokinins and gibberellin A3. Kinetin and gibberellin A3 increased to a similar extent the accumulation of reducing sugars and free amino acids, and reduced that of non‐reducing sugars in the peel during natural maturation. Their differential effect on chlorophyll loss may not be explained through their effects on sugar accumulation. [ABSTRACT FROM AUTHOR]