Promotion of Growth and Flowering of Cyclamen by Root-zone Cooling during Hot Summer Season

Abstract

Cyclamen (Cyclamen persicum Mill.), whose growth and flowering are retarded by high temperatures during the summer season, was used in this experiment to investigate the effect of root-zone cooling on growth and flowering. Root-zone temperatures were preset at 20, 23, and 26°C during the summer season. The control was without root-cooling. Each root-zone temperature was maintained at ±1 to 2°C of the preset temperature. The averages of minimum and maximum temperatures of the control were about 25 and 28°C, respectively. Vegetative growth was promoted at 23°C compared with that of the control. Flowering at 20°C started in the middle of October, and the number of flowers per plant reached about 7 after 20 days. Flowering rates increased with a drop in the root-zone temperature: 20% at the control temperature, 44% at 26°C, 60% at 23°C, and 88% at 20°C. The number of flower buds per plant was maximal at 23°C, and was about 65, having 25 and 10 more than those at 20°C and the control temperature, respectively. In conclusion, root-zone cooling at 23°C significantly promoted both vegetative growth and flower bud formation of cyclamen, and that at 20°C accelerated the flowering rate. Thus, controlling the root-zone temperature between 23 and 20°C may be markedly advantageous for cyclamen cultivation during the hot summer season.