ISHS Acta Horticulturae 179: V International Symposium on Growth Regulators in Fruit Production
CITRUS STYLAR ABSCISSION IN TISSUE CULTURES |
| Authors: | John W. Einset, A. Arboretum |
| Abstract:
This report reviews research on the use of flower explants to study the regulation of Citrus abscission by phytohormones and nutrients and to identify effective growth regulators for fruit production. Beginning with the work of Goldschmidt and Leshem in 1971, the experimental system based on stylar abscission in excised pistils has been exploited to obtain a better understanding of the abscission process. Three classes of phytohormones regulate stylar abscission: 1) auxins (e.g. 2,4-D, 4-chlorophenoxyacetic acid, triclopyr, picloram) are inhibitory, 2) ethylene and ethylene precursors (e.g. l-aminocyclopropane-l-carboxylic acid, ethephon) are stimulatory and 3) cytokinins (e.g. N6-benzyladenine, kinetin, zeatin, N6-isopentenyladenine, thidiazuron) are also stimulatory. In the absence of added auxin or cytokinin, endogenous ethylene controls the timing of abscission. However, if the test medium is supplemented with either auxin or cytokinin, ethylene production can be affected without a corresponding ethylene effect on abscission. Thus, the interaction of phytohormones appears to be hierarchical. The most potent auxin inhibitor of stylar abscission is picloram which has also been shown to be highly effective for two of the major uses of growth regulators in Citrus : 1) prevention of pre-harvest fruit drop in oranges and grapefruits and 2) inhibition of stem (button) abscission in harvested lemon fruits. Therefore, the tissue culture method is a rapid and reliable means for assessing the value of chemicals for commercial use. Nutrients, like phytohormones, can also control stylar abscission in pistil explants. The most critical nutrient in the test medium appears to be sucrose because abscission is completely prevented in its absence. | |
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