Image analysis of internode elongation during light, dark and night interruption in Chrysanthemum

A system for measuring the growth of two or more plants with high-resolution was developed to investigate the effects of environmental factors such as light quality and quantity on plant growth. The new system consists of a CCD camera with an infrared filter and an infrared lighting apparatus to capture plant images during the day and night. The camera system is mounted on a stepping motor controlled by a computer, and the software was developed with Visual Basic. In this study, ten Dendranthema x grandiflorum cv. "Reagan" were arranged in a concentric pattern around the camera system, and the camera captured internode length of the apical part of ten plant images one after another in sync with the stepping motor. The general idea of the relative elongation rate (RER, %/hour) was introduced here. Internode elongation tended to increase during the night in almost all growth stages, and the overall internode elongation profile was determined to be approximately 3% per hour during the day and 6% during the night. Thus, it became clear that RER was promoted during the dark and, consequently, that the elongation of plants can be controlled by adjusting the respective lengths of day and night. These findings could provide fundamental data for research on controlling plant elongation.