Interactions of the Growth Retardants Daminozide and Piproctanyl Bromide, and Gibberellins A1, A3, A4+7, A5 and A13 in Stem Extension and Inflorescence Development in Chrysanthemum morifolium Ramat

Abstract

Interactions between the growth retardants daminozide (a substituted succinamic acid) or piproctanyl bromide (a quaternary ammonium, piperidinium compound), and a subsequent application of a single dose (40 μg) of either gibberellin A1, A3, A4+7 or A12, showed that, in Chrysanthemum morifolium Ramat. cv. Bright Golden Anne, a strong interdependence exists between elongation of the lateral shoot and the rate of development of its terminal inflorescence. A1, A3, and A4+7 were highly active in overcoming the restrictions on both internode extension and the rate of flower-bud development imposed by either retardant, suggesting that these two retardant effects are caused by a deficiency of active gibberellins (GN). In the absence of retardant, A1, A3, and A4+7 markedly increased stem elongation, and flowering occurred earlier than in plants receiving neither retardant nor GN. A13 the only 20-carbon GN tested, was much less active, while A5 had a relatively greater effect on the time of flowering than on shoot elongation. Thus, it is not necessarily the rate of stem extension which determines the rate of inflorescence development. The response to different amounts of A1, A3 or A13 (1, 5, 10, 20, or 50 μg per shoot) neither suggest that different ‘threshold’ levels of a particular GN are required to induce increases in either stem elongation or in the rate at which inflorescences develop, nor did a change in the dose given lead to any consistent differential effect on these two processes.