Nine cultivars of Pelargonium ×domesticum L.H. Bailey were evaluated for the effect of daily light integral on floral initiation. Plants were grown at four daily light integrals: 5, 10, 15, or 20 mol·m-2·d-1 for a 16-hour photoperiod in environmental growth chambers at constant 15.5 °C. Meristems were examined at 50 mol·m-2 intervals for morphological changes associated with floral initiation. Two phenotypes were identified, cultivars with an association between floral initiation and cumulative irradiance and those with association between floral initiation and chronological time. Genotypic variation was observed among the irradiance-associated phenotypes.
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