Effects of Paclobutrazol on Vegetative and Reproductive Growth and Leaf Mineral Content of Mature Apricot (Prunus armeniaca L.) Trees

In the absence of dwarfing rootstocks for apricot (Prunus armeniaca L.), techniques that reduce vegetative growth while enhancing fruit quality and yield are important in the orchard management system. Four year old mature apricot trees cultivars Nasiri, 35Shahroodi, Jahangiri, Shahroodi and Noori on apricot seedling rootstocks, planted at a density of 1250 trees ha-1 and grown at Tarbiat Modarres University (TMU) orchard were used. The effect of soil applied paclobutrazol (0.5 and 2 g tree-1 a.i.) on apricot trees was studied over three years period during 1998-2000 seasons. Treatment effects on vegetative and reproductive growth characteristics and the leaf nutrient status of the apricot trees were determined. Results indicated that paclobutrazol (PBZ) significantly reduced vegetative growth during the experiment. The total pruning dry weight, shoot growth and trunk cross sectional area (TCSA) of treated trees were lower than those of the controls.Although, results showed that fruit load, crop density and total soluble solids (TSS) of fruits were not affected by applied treatments compared with the control. In addition,PBZ decreased nitrogen (N) concentration, but, phosphorus (P), potassium (K) and calcium (Ca) concentrations were not affected by the treatments. Chemical name of PBZ is: (2RS, 3RS)-1- (4-chlorophenyl)-4,4-dimethyl-2-(1H-1,2,4-triazol-1-yl)pentan-3-ol.