Impact of girdling on rooting ability and some biochemical attributes in cuttings of three olive cultivars

•Girdling treatment increases leaf and stem carbohydrates, and enhances rooting.•Easy-to-root cultivar had higher polyphenol concentrations than hard-to-root ones.•Girdling enhanced leaf quercetin concentration in all three cultivars. The rooting ability of olive cuttings varies greatly among cultivars, ranging from hard to relatively easy to root. The present study was conducted as a factorial in a completely randomized block design on leafy cuttings of hard-to-root cultivars, i.e., Conservalia and Amigdalolia and easy-to-root cultivar, i.e., Roghani. Three trees were selected for each cultivar; branches were randomly selected from different orientations on these trees; on July 15, a number of these branches were girdled, while others were left intact. After four months, uniform cuttings were taken from these branches. Our findings demonstrated that the rooting percentage in the Roghani cultivar was significantly higher than in the other two cultivars. Girdling treatment increased this characteristic (60 %) as well as the concentration of carbohydrates in the leaves (30 %) or the bottom part of cuttings (46 %). Nitrogen concentration was not statistically different in various tissues or cultivars. Leaf quercetin concentration in girdled cuttings of all three cultivars (Roghani: 48.12, Conservalia: 110.79, and Amygdala: 145.09 mg.l−1) was higher than in non-girdled samples (Roghani: 31.84, Conservalia: 69.82, and Amygdala: 112.16 mg.l−1). In conclusion, our findings indicate that girdling treatment improved rooting ability by affecting the carbohydrate status of cuttings and certain phenolic compounds such as quercetin.