NOVEL USAGE OF 2,4-D TO INCREASE CITRUS FRUIT QUALITY

Abstract

Fruit splitting is a physiological disorder occurring in a variety of citrus cultivars. It is caused by pressure resulting from the expanding pulp of an individual fruit on its rind, leading to the splitting open and eventual premature drop of the fruit from the tree. There is currently no commercial solution available to the South African citrus producers for this disorder. Foliar sprays of plant growth regulators and/or mineral elements, specifically targeting the rind of the fruit, may be successful in reducing the severity of the disorder in split-prone cultivars. The aim of this study was to evaluate the effect of different foliar sprays on fruit splitting in early and late mandarins, as well as 'Valencia' oranges. Foliar spray treatments commenced after physiological fruit drop and consisted of different combinations of timing and concentration of the plant growth regulators 2,4-dichlorophenoxy acetic acid (2,4-D), gibberellic acid (GA3), as well as calcium (Ca) and potassium (K). Split fruit were removed and counted at two-weekly intervals until harvest, when internal and external quality parameters of treated fruit were also evaluated. Results indicate a significant reduction in split fruit and an increase in fruit diameter after 2,4-D (10 ppm) foliar sprays, as well as in combination with K (5%). Internal and external fruit quality parameters were not negatively affected, except for a slight increase in rind coarseness and reduction of juice content of treated fruit. The application of this synthetic auxin (2,4-D) and its positive reduction of fruit splitting, could be explained by a possible enhancing effect on the growth of the rind’s cells in the stylar-end of the fruit, where fruit split normally begins.