Girdling and the reduction in shoot xylem sap concentrations of cytokinins and gibberellins in peach

The effects of girdling at the beginning of pit hardening on peach shoot xylem sap cytoki- nin and gibberellin concentrations were studied. Girdling at the beginning of growth stage II of fruit development significantly reduced xylem sap concentration of zeatin-type cytokinins, gibberellin A, and/or gibberellin A3. Girdling also reduced shoot growth, both internodal length and node number, for about eight weeks after girdling until the girdle had healed over. The results support the hypothesis that reduced shoot growth is caused by reduced xylem transported, root supplied, promotive growth substances.