Cultivation of ornamental sunflower (Helianthus annuus L.) in vase under different paclobutrazol doses

The sunflower presents propagation easiness, short time for crop and an inflorescence attractive and suitable for arrangements and vases. The great natural growth has been one of the impediments for the sunflower to be explored as ornamental plant. The paclobutrazol, a growth regulator that inhibits the biosynthesis of gibberellins, could be used in several ornamental species, reducing the prolongation of stems. An experiment was conducted to investigate the effect of paclobutrazol on potted "Golden" Sunflower. An 4x4 factorial block randomized designed experiment was established with 4 substrates (soil:sand:carbonized rice husk 2:0,5:2 v/v; soil:sand:fiber sugar cane coal 2:0,5:2 v/v; soil:sand:woodcoal 2:0,5:2 v/v; commercial potting media) and 4 paclobutrazol dosages (0; 2; 4 and 6 mg a.i/pot) with 3 replications. The following characteristics were evaluated: plant height, number of leaves and chlorophyll content based on spad units. Plants grown on substrates with carbonized rice husk and woodcoal exhibited better quality. There was increase of the SPAD units with the increase of the paclobutrazol dosages, and its maximum value was noticed in the dose of 5,08 mg a.i./pot. Paclobutrazol dosages exhibited inverse relation to plant height. The dosage 6 mg a.i./pot of paclobutrazol can be recommended to provide good pot plant harmony.