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

The aim of this study was to examine the environmental regulation of ̄ower initiation and subsequent development in heliotrope (Heliotropium aborescens L. cv. Marine). Five experiments were conducted, two examined whether ̄owering could be advanced by cool temperatures. The duration of cool temperature required to induce rapid ̄owering was also investigated. The ®nal three experiments examined the effects of light integral, photoperiod and temperature on ̄ower initiation and development. It was found that plants grown for 9 days at 108C and than transferred to 208C ̄owered signi®cantly earlier (®rst ̄owering recorded after 55 days) than plants held constantly at 208C (65.9 days to ̄owering). Plants grown at a constant temperature of 208C had signi®cantly more leaves than all other treatments. This suggested that `cool' temperatures, prior to initiation, advanced ̄owering. In a transfer experiment, plants were moved from 10 to 208C at 3 days intervals postpinching. Earliest ̄owering (by 20 days compared to the 208C constant treatment) occurred when plants were exposed to 108C for 9 days and then transferred to 208C. Photoperiod was shown to have no effect on either ̄ower bud initiation or development (postinitiation). Both temperature and light integral strongly in ̄uenced ̄ower development post̄ower bud initiation. However, the response to temperature plotted in terms of the reciprocal of days to ̄owering was non-linear. # 2000 Elsevier Science B.V. All rights reserved.