Comparative effects of four plant growth retardants on growth ofEpidendrum radicans

SummaryThe effect of paclobutrazol, triapenthenol, daminozide and chlormequat chloride on the growth of Epidendrum radicans was studied over one year. Paclobutrazol and triapenthenol were applied as soil drenches at 5, 10 and 20 mg –1, while 1000, 2000 and 4000 mg l–1 daminozide and 2000, 4000 and 6000 mg l–1 chlormequat chloride were applied as foliar sprays. Main and lateral shoot growth restriction (54-75%) was obtained by all doses of paclobutrazol and 20 and 10 mg l–1 triapenthenol. Daminozide at 4000 and 2000 mg l–1 restricted only main shoot growth. Chlormequat chloride at 6000 mg –1 had a similar effect but caused leaf toxicity symptoms, as white spots. The effect of the four growth retardants on shoot growth restriction followed the order paclobutrazol>triapenthenol> daminozide>chlormequat chloride. The number of lateral shoots developed during the treatment period and the main and lateral shoot diameter were not affected by any chemical used. Leaf length was much reduced (46-62%) by all doses of paclobutrazol and the two higher doses of triapenthenol and to a lesser extent (13-29%) by all doses of daminozide and the lower dose of triapenthenol, while it was not affected by chlormequat chloride. Leaf width was restricted (13-37%) by the two higher doses of paclobutrazol, triapenthenol and daminozide and the highest dose of chlormequat chloride. Leaf thickness was much increased (52-76%) by all doses of paclobutrazol and the two higher doses of triapenthenol. The lower dose of triapenthenol and daminozide, and all doses of chlormequat chloride, caused a smaller increase in leaf thickness (17-37%). Seven and a half months after the end of treatments paclobutrazol was the most persistent of the growth retardants used. For compact E. radicans pot plants, without special needs of support, a 10 mg l–1 paclobutrazol soil drench applied monthly is recommended.