GROWTH-REGULATOR EFFECTS ON PLANT HEIGHT OF POTTED MUSSAENDA QUEEN SIRIKIT

Mussaenda L., a tropical ornamental shrub developed in the Philippines , has been examined as a potential potted floriculture crop in the Uni ted States because of its showy white, picotee (white with pink margin s), pink or red sepals and fragrant, yellow flowers. However, the prof use upright growth habit of some Mussaenda cultivars is undesirable fo r pot plant culture. Three growth regulators, daminozide (B-Nine), anc ymidol (A-Rest), and packobutrazol (Bonzi), were applied at two commer cially recommended rates and two application methods (spray vs. drench ) to determine their effects on plant height. Treatments (all concentr ations as active ingredients) were daminozide spray (2500 or 5000 mg.L -1), ancymidol spray (33 or 66 mg.L-1), ancymidol drench (0.25 or 0.50 mg/pot), paclobutrazol spray (25 or 50 mg.L-1), and paclobutrazol dre nch (0.125 or 0.25 mg/pot). In subsequent experiments, the same growth regulators were applied at higher concentrations and in either two or three applications. The most attractive potted plants were produced w ith two spray applications of daminozide at 5000 mg.L-1 or two drench applications of ancymidol at 0.5 mg/pot. Higher concentrations or addi tional applications excessively reduced plant height. Paclobutrazol sp rays or drenches at any concentration or application number were ineff ective for controlling plant height. Chemical names used: opropyl-a-(4 -methyoxy-phenyl)-5-pyrimidinemethanol (ancymidol); succinic acid 2,2- dimethyl-hydrazide (daminozide); -a-(1,1-dimethylethyl)-1H-1,2,4-triaz ole-1-ethanol (paclobutrazol).