Seed dormancy in Papaver rhoeas is affected by the time of emergence of mother plants.

Poppy ( Papaver rhoeas L.) is a major dicot weed in winter cereals in Spain with an extended period of emergence from October (autumn) to April (spring). During 2003/2004, seed was established as two autumn cohorts (without crop), two winter cohorts (with and without barley), and two spring cohorts (with and without barley), in a trial conducted in the north-east of Spain. The seeds of each cohort were collected and, after four months, their germination was assessed in two assays. In the first assay, seeds were subjected to dark stratification at three temperature ranges (5/15, 10/20 and 25/15°C) for up to 12 weeks. Samples were germinated periodically at 5/15, 10/20 and 25/15°C with a 12 h photoperiod to determine dormancy status. In the second assay, seeds were sown in pots placed outdoors at three times during the emergence period (October, December and April) to monitor emergence and dormancy release. The optimal temperature regimes for germination were 5/15 and 10/20°C. The spring cohorts had less seed dormancy and greater germination than all other cohorts. These differences probably related physiological factors determining seed dormancy in late cohorts, which has implications for poppy management in cropping systems in north-east Spain.