© 2001 Heron Publishing—Victoria, Canada
Induction of flowering in tropical trees by a 30-min reduction in photoperiod: evidence from field observations and herbarium
specimens
Guillermo Rivera (1) and Rolf Borchert (2, 3)
1. Instituto Multidisciplinario de Biología Vegetal, Universidad Nacional de Córdoba, Casilla de Correo 495, 5000 Córdoba, Argentina / 2. Division of Biological Sciences, Haworth Hall, University of Kansas, Lawrence, KS 66045-2106, USA / 3. Author to whom correspondence should be addressed (borchert@ukans.edu) / Received February 24, 2000
Summary
During the late rainy season in October 1997 we observed, over a range of > 100 km, the highly synchronous emergence of flower
buds in several deciduous tree species of the semi-deciduous tropical forest in Guanacaste, Costa Rica. Synchronous flowering
soon after the rapid decline in day length around the September equinox and in the absence of any notable climatic cues suggested
flower induction by declining photoperiod. By combining field observations and the analysis of flowering herbarium collections,
we established highly synchronous flowering periods with low interannual and latitudinal variation predicted for photoperiodic
flower induction for more than 25 tree species and a few herbs. We describe morphogenetic changes at the shoot apex of three
species during flower induction and the suppression and induction of flowering in several herbaceous species by experimental
daylight extension. The combined observations provide strong, mainly indirect evidence for photoperiodic induction of flowering
in many tropical tree species. At low latitudes with annual variation in day length of 1 hour, flower induction must be caused
by a decline in photoperiod of 30 min or less. This is the first report of photoperiodic control of flowering in trees.
Keywords:
flower induction, tropical dry forest.
