Effects of exogenous growth regulator applications on source-leaf carbohydrate accumulation patterns in ponkan (Citrus reticulata Blanco)

Abstract

This study focused on the effect of exogenous gibberellic acid (GA3), auxin (2, 4-D), and synthetic urea-based cytokinin (CPPU) and their application time on non-structural carbohydrate partitioning in the leaves and the interaction with fruit development in ponkan (Citrus reticulata Blanco cv. Yoshida), a low yielding citrus cultivar. Hormones were applied at: 200 ppm GA3, 10 ppm 2, 4-D, and 20 ppm CPPU, either singly or in combination at anthesis and/or 30 days later. GA3 applied 30 days after anthesis increased the proportion of sucrose to glucose and fructose in the sap and reduced starch content. The increase in sucrose appeared 60 days after anthesis but starch decrease occurred 120 days after anthesis. Double application did not exert any significant effects. 2, 4-D treatments reduced fruit set slighthy, but did not affect sugar accumulation patterns. A single application of CPPU or in combination with other growth regulators at anthesis increased total sugar content, reduced fruit set, caused severe leaf chlorosis, and leaf drop.