Enhancement of IBA stimulatory effect on rooting of olive cultivar stem cuttings

Three groups of olive cultivars were characterized as showing low, moderate or high rooting percentage after application of indole-3-butyric acid (IBA) treatment. To improve the rooting of olive cuttings, urea-phosphate (UP) and paclobutrazol (PB) were tested in combination with IBA. UP alone did not stimulate rooting of olive cuttings; however, when applied together with IBA it significantly enhanced the rooting of cultivar 'Manzanillo' cuttings. PB alone had a weak effect on rooting of cuttings but in combination with IBA it improved the rooting of cultivars 'Manzanillo' and 'Souri' cuttings. A triple combination of IBA, UP and PB provided the most effective treatment for the improvement of rooting percentage. IBA treatments increased the number of roots per cutting in comparison with the control, but decreased the length of the roots of cultivar 'Barnea'. IBA plus UP or PB further increased the number of newly formed roots. However, IBA plus UP markedly increased root length. The three compound treatment did not differ from IBA plus PB regarding root number per cutting, but the roots were longer than in IBA treated and control cuttings. The survival of rooted cuttings treated with IBA was relatively low, for all cultivars tested. IBA plus UP plus PB improved the survival of the rooted olive plants compared with IBA alone. Thus UP and PB were shown to enhance the effect of IBA in stimulation of rooting and survival of olive cuttings.