White poplar (Populus alba L.) is an ornamental tree used in urban environments. We evaluated the effect of 0.4 and 0.8 g of paclobutrazol (PBZ) per plant on the growth and vitality of white poplar trees that were severely pruned. The experimental design was completely randomized with five replications. The application of PBZ significantly (P ≤ 0.05) affected trunk growth, leaf growth and the total/reducing sugars ratio. However, the effect was lost in the next growth period. Thus, the overall effect is null in improving the vitality of this species, since the chlorophyll fluorescence values (Fv/Fm) were diminished after the treatment. Further research is suggested in order to improve the understanding of PBZ effect on white poplar.

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