Influence of Light and Temperature Upon Leaf and Bract Abscission in Poinsettia1

Abstract Flowering plants of several cultivars of poinsettia, Euphorbia pulcherrima Willd, were placed in darkness or low intensity artificial light to determine their influence on induction or retardation of abscission of leaves and bracts. Photoperiod was not a factor in abscission control but abscission of leaves and bracts was induced in darkness. Light of 25 or more ft-c intensity had an effect in delaying abscission. Longer light periods were more effective and continuous 25 ft-c light was as effective in delaying abscission as 8 hr of 225 ft-c light. Continuous 225 ft-c light delayed abscission for periods up to 60 days. Leaves tended to abscise before bracts in darkness and bracts before leaves in low intensity light. Higher light intensities were required to delay abscission following longer dark periods than following shorter or no dark storage. Leaf and bract abscission were promoted by 11 days of darkness and delayed by 75 ft-c light in cv. ‘Elisabeth Ecke’ while the long lasting cv. ‘New Ecke White’ required 16 days for promotion of leaf abscission (bract abscission was not promoted by 16 days of darkness) and 25 ft-c light was capable of delaying abscission.