Environmental regulation of flowering time in heliotrope ( Heliotropium arborescens L. cv. Marine)

Abstract

The aim of this study was to examine the environmental regulation of flower initiation and subsequent development in heliotrope ( Heliotropium aborescens L. cv. Marine). Five experiments were conducted, two examined whether flowering could be advanced by cool temperatures. The duration of cool temperature required to induce rapid flowering was also investigated. The final three experiments examined the effects of light integral, photoperiod and temperature on flower initiation and development. It was found that plants grown for 9 days at 10°C and than transferred to 20°C flowered significantly earlier (first flowering recorded after 55 days) than plants held constantly at 20°C (65.9 days to flowering). Plants grown at a constant temperature of 20°C had significantly more leaves than all other treatments. This suggested that ‘cool’ temperatures, prior to initiation, advanced flowering. In a transfer experiment, plants were moved from 10 to 20°C at 3 days intervals post-pinching. Earliest flowering (by 20 days compared to the 20°C constant treatment) occurred when plants were exposed to 10°C for 9 days and then transferred to 20°C. Photoperiod was shown to have no effect on either flower bud initiation or development (post-initiation). Both temperature and light integral strongly influenced flower development post-flower bud initiation. However, the response to temperature plotted in terms of the reciprocal of days to flowering was non-linear.