Gibberellin- and Cytokinin-induced Growth and Flowering Responses in Rudbeckia hirta L.

Abstract

BA and GA4+7, were applied to vegetative, mature Rudbeckia hirta plants at the beginning of long days (LD). There were no synergistic effects, but BA inconsistently affected branching and had no effect on flowering. Floral initiation of the terminal inflorescence was promoted by GA4+7, although axillary inflorescences were not. Increasing GA4+7 levels decreased the time to terminal inflorescence anthesis. However, the interval between the terminal and second axillary inflorescence anthesis was increased. The net result was no significant effect on the time to second axillary inflorescence anthesis. Gibberellins may enhance the LD effect on the apical meristem of Rudbeckia, but axillary meristems, which initiate later, remained unaffected. Chemical names used: benzyladenine (BA), gibberellin4+7, (GA4+7).