Influence of paclobutrazol and bulb sizes on seed yield and yield attributing traits of onion (Allium cepaL) cv Taherpuri

Different doses of paclobutrazol (PBZ) and different bulb sizes of onion were evaluated to determine their effect on growth and seed production of onion. Onion variety ‘Taherpuri’ with three-bulb sizes – small, medium and large – was used. Four doses of PBZ were 0 (control), 20, 40, and 80 mg l−1. The two-factor experiment was laid out in a randomized complete block design with three replications. Application of PBZ significantly reduced the plant height, tillers per bulb, leaves per plant and length of scape. However, in other parameters such as the number of flowers, umbels per bulb, umbel diameter, 1000-seed weight and seed yield, there were no significant influences of PBZ concentrations used (p < 0.05). On the contrary, plant height, number of leaves per plant, length of scape, effective fruits per umbel, percentage of fruit set, and seed yield were positively influenced by different bulb sizes of onion. Higher values were obtained for the above-mentioned parameters from the larger-sized bulbs and values were decreased as the bulb sizes decreased. The maximum seed yield was recorded in plants grown from the large-sized mother bulb. The interaction between the PBZ doses and bulb sizes were also significant for some variables while it was not significant for others.