Photoperiod Sensitivity during Flower Development of Opium Poppy (Papaver somniferum L.)

Flower development in opium poppy ( Papaver somniferum L. `album DC') is enhanced by long photoperiods (PP ≥ 16-hours). Predicting time to flower in field-grown opium poppy requires knowledge of which developmental stages are sensitive to PP and how the rate of flower development is changed by changes in PP. The objective of this work was to determine when poppy plants first demonstrated developmental changes in response to PP and how long PP continued to influence the time to first flower under consistent temperature conditions. Plants were grown in artificially lit growth chambers with either a 16- (inductive) or a 9-hour PP (noninductive). Plants were transferred at 1 to 3-day intervals from a 16- to a 9-hour PP and vice versa. All chambers were maintained at a 12-hour thermoperiod of 25/20°C. Poppy plants demonstrated developmental changes in response to PP four days after emergence and required a minimum of four inductive cycles before the plant flowered. Additional inductive cycles, up to of a maximum of nine, hastened flowering. After 13 inductive cycles, flowering time was no longer influenced by PP. These results indicate four phases between emergence and first flower: 1) a photoperiod-insensitive juvenile phase (JP); 2) a photoperiod-sensitive inductive phase (PSP); 3) a photoperiod-sensitive post-inductive phase (PSPP); and 4) a photoperiod-insensitive post-inductive phase (PIPP). The minimum durations (days) of these phases under the conditions of our experiment were JP = 4, PSP = 4, PSPP = 9, and PIPP = 14.