Relationship of Carbohydrate Sources and Indole-3-Butyric Acid in Olive Cuttings

Abstract

Indole-3-butyric acid (IBA) treatment improves rooting of easy-to-root and moderate-rooting olive cultivars, but does not stimulate root formation in hard-to-root cultivars. The rate of root formation in olive cuttings is slow and a source of carbohydrates is required to maintain and improve the effect of IBA. Sucrose treatment applied together with IBA and several times thereafter improved all rooting parameters: rooting percentage, number of adventitious roots and root length. During rooting, photosynthesis in the cuttings is very low and has almost no effect on the carbohydrate content, so that starch appears to be the major source of carbohydrates. Amyloplast levels decline during rooting and IBA increases the rate of their disappearance. A significant percentage of rooted olive cuttings collapse during their hardening process, when no starch pool is available. Only photosynthesis of fully-expanded leaves can contribute to the source of the carbohydrates needed by the rooted plants. However, when the top growth is reduced, as often occurs in IBA-treated cuttings, the carbohydrate supply may not be enough to keep the rooted plants alive and to support their growth and development. The data suggest that carbohydrates have an important role in rooting and improve the stimulatory effect of IBA in this process. During the stages involved in the formation of adventitious roots the endogenous carbohydrate pool is the main source of carbohydrates, while in young rooted plants the main source comes directly from the photosynthesis.