Effects of Growth Regulator Chlormequat Chloride on Severity of Three Bacterial Diseases on 10 Cultivars of Hibiscus rosa-sinensis. A. R. Chase, Associate Professor of Plant Pathology, University of Florida, IFAS, Agricultural Research and Education Center, 2807 Binion Rd., Apopka 32703. L. S. Osborne, J. M. F. Yuen, and B. C. Raju. Assistant Professor of Entomology, and Biological Scientist II, University of Florida, IFAS, Agricultural Research and Education Center, 2807 Binion Rd., Apopka 32703, and Chief Plant Pathologist, Yoder Brothers of Florida, Inc., P.O. Box 68, Alva 33920. Plant Dis. 71:186-187. Accepted for publication 24 September 1986. Copyright 1987 The American Phytopathological Society. DOI: 10.1094/PD-71-0186.

The effects of the growth regulator chlormequat chloride on severity of bacterial diseases caused by Pseudomonas cichorii, P. syringae pv. hibisci, and Xanthomonas campestris pv. malvacearum was evaluated on 10 cultivars of Hibiscus rosa-sinensis. Plants treated with chlormequat chloride had fewer leaves (mean of two to four per plant) and were 3.8–12.7 cm shorter than untreated plants. The mean severity of disease caused by P. cichorii on 10 cultivars was reduced an average of 33.9% in three tests for plants treated with chlormequat chloride. The mean severity of disease caused by P. syringae pv. hibisci on these cultivars was reduced by 68.5% for three tests when plants were treated with chlormequat chloride. The mean severity of disease caused by X. campestris pv. malvacearum on nine cultivars was reduced an average of 47.9% for three tests when plants were treated with chlormequat chloride. There were no differences in susceptibility of the cultivars to P. cichorii. However, plants were differentially susceptible to P. syringae pv. hibisci; cultivars White Red Eye and President were very resistant, and Brilliant Red, Painted Lady, and Holiday were very susceptible. Cultivars Senorita and American Beauty were most susceptible to X. campestris pv. malvacearum, and Euterpe was very resistant.