Effect of plant growth retardants on stem elongation of hibiscus species

One-time spray applications [about 6 mL(0.2 fl oz)] of chlormequat chloride [1000 or 2000 mg·L^-1 (ppm)], daminozide (2500 or 5000 mg·L^-1), paclobutrazol (20 or 40 mg·L^-1) and uniconazole (5 or 10 mg·L^-1) varied in efficacy in reducing Hibiscus coccineus (Medic.) Walt., H. radiatus Cav., and H. trionum L. (flower-of-an-hour) stem elongation. Chlormequat chloride inhibited stem elongation of all species, with a 2000 mg·L^-1 application reducing stem length of H. coccineus, H. radiatus, and H. trionum by 87%, 42%, and 52%, respectively, compared to untreated plants, 28 d after application. Paclobutrazol also inhibited stem elongation of all species. Uniconazole reduced stem elongation of H. coccineus and H. radiatus, but not H. trionum. Daminozide applied at 5000 mg·L^-1 reduced H. radiatus stem elongation only. Growth retardants examined in this study did not delay flowering of H. trionum, the only species that flowered during the experiment. (Chemical names used: ancymidol (α-cyclopropyl-α-(4-methoxyphenol)-5-pyrimidinemethonol), chlormequat chloride(2-chloroethyltrimethylammonium chloride), paclobutrazol ((+)-(R*,R*)-beta((4-chlorophenyl)methyl)-alpha-(1,1-dimethyl)- 1H-1,2,4-triazol-1-ethanol), daminozide ([butanedioic acid mono(2,2-dimethylhydrazide)], uniconazol-P ((E)-(+)-(s)-1-(4-chlorophenyl)-4,4-dimethyl-2-(1,2,4-triazol-1-yl)pent-1- ene-3-ol)).