Online) An Open Access

ABSTRACT In this research, the effects of various gibberellic acid concentrations (0, 25, 50, 150, and 450 ppm) on stem length uniformity, umbel maturity, and seed quality and quantity of the onion cultivar Azarshahr were studied. The treatments were applied when the first flowering stems emerged. Results of ANOVA indicated that this growth regulator had its greatest effects on the mentioned characteristics at 50 and 150 ppm, and that seed yield increased by about 25% through application of gibberellic acid at 50 ppm. However, in all, concentrations of 50, 150, and 450 ppm had the same level of effects. The effects of these treatments on the average number and length of emerged stems and on the time of umbel maturity were not significant, but the treatments had significant effects on seed quality and treated plants had higher percentages of normal seedlings and greater dry weights