Effect of paclobutrazol on growth of young potted flame tree (Delonix regia (Hook.) Raf.)

The planting of street trees is a common feature to support a good urban environment. The negative interaction between tree roots and construction results in sidewalk damage often happening especially in cities in tropic regions, due to the long period of seasonal growth. Thus the technique for retarding growth should be investigated. This study aimed to evaluate the effect of paclobutrazol (PBZ) application on growth responses in a young flame tree (Delonix regia (Hook.) Raf.). Uniform five-months-old seedlings were cultured in a plastic pot and once applied as a soil drench at 0 ( control), 2, 4, and 8 g active ingredient (a.i.). The study was done at a plant nursery of Kasetsart University, Bangkok, Thailand (N 13.847531; E 100.571396). Six and half months later, shoot and root growths were evaluated. In PBZ treated plants progressively short shoot length was found and vice versa to dose increase. High dose PBZ at 4 and 8 g a.i. reduced total root length; however, low dose; 2 g a.i. enlarged instead. The concentration at 4 g a.i. significantly affected the reduction in root length with acceptable shoot performances. Soil applied with PBZ might be a potential way to retard growth performance for street trees.