Modification of hibiscus growth by treating unrooted cuttings and potted plants with uniconazole or paclobutrazol

Abstract

Unrooted cuttings ofHibiscus rosasinensis L. “Seminole Pink” were soaked for 5 s in a solution containing 25, 50, 75, or 100 mg L−1 uniconazole or paclobutrazol, rooted, and then potted and allowed to grow without pinching. Uniconazole was more effective than paclobutrazol in suppressing stem growth and number and length of lateral shoots. Uniconazole and paclobutrazol, at the 25 mg L−1 concentration, resulted in stem growth 75 and 25%, respectively, of the control, with further reduction at higher rates. Flowering was delayed by the highest rate of uniconazole but not paclobutrazol. Flower number was reduced by both retardants, without any effect on flower size. Plants treated with uniconazole had short pedicels regardless of the rates, whereas paclobutrazol did not affect pedicel length. A second experiment used unrooted cuttings being soaked in a solution containing 0, 12.5, 25, or 50 mg L−1 uniconazole or having the lower 2.5 cm of the stem dipped in a solution containing 0, 50, 100, or 200 mg L−1 uniconazole. Plants were pinched after potting. Soaking resulted in more efficient height control than dipping. Lateral shoot number was reduced by soaking but not dipping. All treated plants had smaller stem diameters. Flower size was unaffected regardless of method of treatment and the type of retardant applied. In a third experiment, soil drenches with uniconazole at a rate as low as 0.05 mg/pot resulted in excessive growth retardation. Soil drenches with paclobutrazol at 0.05–0.20 mg/pot reduced shoot growth, flower number, and pedicel length, but did not affect days to bloom.