Comparative Plant Growth-retarding Activities of Ancymidol with ACPC, Phosfon, Chlormequat, and SADH on Ornamental Plant Species1

Chemical growth retardants are unique in the history of chemical regulation of plants. All types thus far used by growers have been synthetics. Unlike many other classes of growth regulators, we have thus far not detected the naturally occurring chemicals that account for the development of dwarf plants. For one reason, dwarf plants may result from reduced or degenerated biosynthetic pathways for the natural production of gibberellin-like compounds. Also, they may result from the synthesis of a number of interrelated compounds, which separately have little effect on growth. In certain combinations and concentrations, however, they affect cell division and expansion control systems. Chemical growth retardants permit a direct approach to growth control by retarding internode elongation without seriously disrupting the growth processes that involve chlorophyll and phytochrome. They permit growers to predetermine the size of the plant for many different uses and have become an integral part of many plant production systems (Fig. 1). Florists’ and nurserymen’s catalogs designate cultivars as particularly responsive to a specific chemical growth retardant.