Bolting induction in Oenothera erythrosepala Borbás in relation to rosette size, vernalization, and photoperiod

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Abstract
The relationships between rosette size, vernalization, and photoperiod in bolting induction of Oenothera erythrosepala (a facultative biennial) were examined. A natural population of O. erythrosepala in a sand dune system at Azigaura, Japan, behaves as a monocarpic perennial, while a population treated with fertilizer showed the life cycle of a winter annual. In both natural and fertilized populations, bolting was restricted to size classes with rosette diameter greater than 9 cm, regardless of the chronological age and the amount of food reserves accumulated in the tap root. Pot culture experiments showed that the species requires both vernalization and long-day photoperiod for bolting induction, and has a critical leaf area for receiving photoperiodic stimuli. The amount of food reserves in the plant per se does not contribute to the size-dependent flowering of the species.