Effect of hand pinching and plant growth regulators on seed production of field qrown hybrid dahlia

Abstract

The effects of hand pinching above node four on the main stem and the application of the plant growth regulators paclobutrazol and chlormequat chloride on seed production of field grown hybrid dahlia ‘Unwins Mixed’ were investigated over two seasons at the same site. Pinching reduced the spread of flowering and resulted in seed heads at approximately the same height above ground level because of the promotion of lateral branch length, but did not increase seed yield. Seed yield per plant was significantly increased following the application of chlormequat chloride at 1.5 kg a.i./ha at stem elongation in the first season, and by paclobutrazol applied at 1.0 kg a.i./ha at the appearance of the first visible flower bud in both seasons, the former through the production of more seed heads/plant, and the latter through a significant increase in seeds/seed head in one season and seed heads/plant in the following season. Other seed yield components did not differ among treatments. Plant growth retarding effects were transitory and floral development and flower numbers were not altered by the plant growth regulators. Although results were inconsistent, chemical manipulation of this hybrid dahlia shows promise for seed production and warrants further investigation. © The Royal Society of New Zealand 1994.