Growth of potted sunflower in response to paclobutrazol

Sunflower, besides being an oil seed crop, is also grown as an ornamental plant. However, its great growth in height makes such use difficult, especially as pot flower. This study aimed to evaluate the effects of the growth regulator paclobutrazol on the growth of potted sunflowers in a hydroponic system, in pots filled with milled silica in a greenhouse. Two sunflower genotypes BRS Oásis with brown head and average height of 1,85 m and Helio 358, with yellow head and average height of 1,45 m. The rates of paclobutrazol evaluated were 0; 0.5; 1; 2; 4 and 6 mg L-1, directly applied on the milled silica substrate. The plants were maintained in Hoagland nutrient solution under constant aeration. The experiment was arranged in a factorial complete randomized block , design with five repetitions, totaling 60 plots. The variables evaluated were plant height, dry phytomass of root, stem, leaves and heads. There was no effect of paclobutrazol on plant growth. Paclobutrazol reduced the height of cultivars Helio 358 and BRS Oásis at all rates. Rates higher than 2 mg L-1 and 4 mg L-1 reduced the growth of the genotypes BRS Oásis and Helio 358 respectively. Sensitivity to paclobutrazol is greater for the genotype Helio 358 than forBRS Oásis.

growth regulators; plant height; Helianthus annuus L

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