Phases of Development to Flowering in Opium Poppy (Papaver somniferum L.) under Various Inductive Photoperiods

Abstract

Four phases of development from emergence to anthesis of the opium poppy (Papaver somniferum L.) are recognized based on transfer studies using 9- and 16-hour photoperiods: a photoperiod-insensitive juvenile phase (JP), a photoperiod-sensitive inductive phase (PSP), a photoperiod-sensitive postinductive phase (PSPP), and a photoperiod-insensitive postinductive phase (PIPP). The objective of this experiment was to determine how the durations of the photoperiod-sensitive phases changed when the plants were exposed to different photoperiods. Plants were grown in lamplit growth chambers with a 12-hour thermoperiod of 25 °C day/20 °C night. They were transferred from a noninductive 9-h to an inductive 12-, 14-, or 16-hour photoperiod or vice versa at 1- to 4-day intervals to determine the durations of the four phases. The average number of days to flower by plants grown continuously in a 16-hour photoperiod was 32 days. Days to flower were delayed by 10 days in the 14-hour photoperiod and by 36 days in the 12-hour photoperiod. The durations of the four phases were not equally affected by photoperiod. The first three phases were photoperiod-dependent, the photoperiod effect being nonlinear. The durations of JP, PSP, and PSPP were 3, 5, and 17 days in the 16-hour; 4, 8, and 23 days in the 14-hour; and 7, 14, and 40 days in the 12-hour photoperiod, respectively. The final phase was not sensitive to photoperiod (i.e., PIPP lasted 7 days regardless of photoperiod). Based on these results, we conclude that the so-called juvenile phase cannot be regarded as photoperiod-insensitive. To model the development of opium poppy under field conditions, a knowledge of daylength as early as seedling emergence may be necessary. The number of inductive cycles needed for floral induction and the rate of floral development largely depend on the photoperiod experienced.