The effects of gibberellic acid and short-day treatments on growth and flowering of Chrysanthemum morifolium cv. Breeze cassus

Abstract

Chrysanthemum morifolium cv. Breeze cassus that is widely grown as a commercial pot plant in South Africa grow short and branch poorly under the usual photoperiodic conditions. It was hypothesised that understanding the effects of gibberellic acid (GA₃), a plant hormone that promotes flowering and stem elongation in plants, may aid in improving its quality. To study this, the vegetative growth and flowering characteristics of Chrysanthemum morifolium cv. Breeze cassus plants treated with GA₃ once, i.e., three weeks after transplanting, GA₃ twice, i.e., three and five weeks after transplanting, gibberellin biosynthesis inhibitor, daminozide, and short-day photoperiod were evaluated. Data was collected on plant height, number of branches per plant, time to flowering, flower buds per plant and flower size and subjected to analysis of variance. Plants treated with a short day photoperiod flowered early compared to the control. However, the plant height and flower buds per plant were significantly (p < 0.05) reduced. The final plant height of short-day photoperiod and daminozide treated plants were not statistically (p > 0.05) different. Both GA₃ treatments significantly (p < 0.05) increased plant height compared to the control, daminozide and short-day photoperiod treated plants. Plants treated with GA₃ twice were significantly (p < 0.05) taller compared to plants treated with GA₃ once. Treatment with GA_3, either once or twice, had no effect on time to flowering, however, treating plants with GA₃ once, significantly increased flower buds and treating plants with GA₃ twice significantly increased flower diameter compared to the control. It was noted that treatment of Chrysanthemum morifolium cv. Breeze cassus with short-day photoperiod and GA₃ have different effects on plant growth and flowering. It was, therefore, concluded that, although GA₃ increases plant height of Chrysanthemum morifolium cv. Breeze cassus, it may not replace short day photoperiod treatment where early flowering is desired.