Temperature and photoperiod effects on the growth and development of opium poppy (Papaver somniferum)

The research described in this paper seeks to address knowledge gaps relating to leaf growth, flowering response to photoperiod and pre-emergent growth for opium poppy (Papaver somniferum), with a view to developing a new decision-support crop model. The pre-emergent growth phases of the commercial morphine cultivar CO58-34 were measured in 10 temperature treatments ranging between 1.5 and 34°C. Linear models fitted to the lag and linear phase growth rate v. temperature plots gave a thermal time duration for the lag phase of 32 degree days and 8.3 degree days per mm of hypocotyl growth for the linear hypocotyl elongation phase. In a second trial, two cultivars (CO58-34 and the thebaine cultivar WF01-1822) were grown in a range of photoperiods spanning 8 to 24 h. Data was also collected on leaf growth attributes. The response to photoperiod was typical for a long day plant. In photoperiods greater than ∼18 h, floral initiation occurred in a minimum, constant thermal time. At shorter photoperiods, initiation was progressively delayed. A second plateau in initiation response to photoperiod occurred for daylengths less than ∼12 h. The duration of the basic vegetative period was similar for the two cultivars at ∼324 degree days from emergence. After an initial delay before the growth of the first fully expanded leaf, leaf appearance rates ranged between 45 and 50 day degrees per leaf. Leaf senescence rates varied between 56 and 84 day degrees per leaf. Leaf area profiles were typically parabolic in nature. Maximum leaf area occurred between nodes 13 and 16 at a value of 12 000-15 000 mm 2.