Effects of topping and foliar application of gibberellic acid on some growth and flowering chracteristics of African marigold

One of the characteristics of ornamental foliage plants is the production of enough leaves and lateral branches to create a dense appearance. In some cases, it is necessary to treat some non-growing branches with some growth regulators to produce enough leaves and lateral shoots. The most common treatments are topping the branch and gibberellic acid application to produce more foliage on the plant. This research was conducted to study the influence of topping and application of gibberellic acid on vegetative and reproductive growth of African marigold as a bedding plant. In this study, topping as the first factor at three levels (0, 45, and 90 days before transplanting) and gibberellic acid as the second factor at four levels (0, 100, 200, and 300 mg L-1) were applied in a pot experiment outdoor under a factorial experiment with a completely randomized design, 4 replications in each treatment (4 pots in each replication). The seeds were planted in late summer. Then, approximately 7 cm long seedlings with six leaflets were transferred to pots. Plants were treated with gibberellic acid and topping 15 to 20 days after transplanting. Foliar spraying was carried out at three stages with 10 days’ intervals. Distilled water was sprayed on control plants. Results showed that using of gibberellic acid combined with a topping treatment increased the amount of chlorophyll index, plant height, length, and lateral roots volume. The number of opened flowers, bud and stem diameter had the highest performance at 120 days after spraying with 100 mg L-1 gibberellic acid. Therefore, topping combined with gibberellic acid at the concentration of 100 mg L-1 increased flowering and most other characteristics studied.