Effect of paclobutrazol on physiology, growth and yield of sunflower (Helianthus annuus L.)

The study investigated the effect of paclobutrazol (PBZ), a gibberellin synthesis inhibitor, on common sunflower (Helianthus annuus L.) plants. Sunflower plants were treated with 10, 20, 50, 100 and 250 mg active ingredient of PBZ per plant as soil application in polybags at 12 days after sowing (DAS). PBZ treatment in sunflower plants resulted in short and compact plants with dark green leaves with increased chlorophyll and carotenoid contents over control at 56 DAS. Plant height was significantly lesser in PBZ-treated plants than in control, with no significant difference in the girth of the plants. PBZ treatment increased root volume by 90.8%, root dry weight by 62.5%, and root–shoot ratio by 82.8% in 10 and 20 mg PBZ treatment. Net photosynthesis rate (PN) and stomatal conductance (gs) were decreased in PBZ-treated plants. Days to maturity were reduced to 73 DAS in 250 mg of PBZ-treated plants as compared to control (106 DAS). 100-Seed weight and seed yield per plant increased by 25.3% and 23.6% respectively, in PBZ-treated plants over control treatment. Application of PBZ resulted in higher epicuticular wax content, fibrous root development, more root volume, and higher root–shoot ratio. These characteristics may impart drought tolerance to sunflower plants during the Kharif season. The lesser height–girth ratio may confer lodging resistance in PBZ-treated sunflower plants.