[Flower bud differentiation and development of opium poppy (Papaver somniferum L.) II. Effects of daylength and temperature].

We investigated the effect of daylength (from 9 to 15 hours) and cultivation temperature (from about 13 to 25 degrees C) on flower bud differentiation of three strains of Papaver somniferum L. cv. Ikkanshu, which have been cultivated in Nayoro (Hokkaido), Tsukuba (Central Honshu) and Nagasaki (Kyushu) for the last a few decades. 1. The experiment on the effect of daylength on flowering revealed that the longer the photoperiod was, the earlier flowering occurred. 2. Flower bud differentiation was observed at temperatures of 20 degrees C or less but never at 25 degrees C, and it was more quickly induced at lower temperatures. Furthermore, we also found that the optimum temperature for flower bud development following differentiation was 20 degrees C. From these findings, we reached the conclusion that this species has thermosensitivity. 3. Flower bud differentiation clearly occurred later in the Nayoro strain than in the Nagasaki strain or the Tsukuba strain. This seems to indicate that the Nayoro strain is a different ecological type from other strains. 4. When we compared the size and dry weight of the capsules, which are known to be closely related to opium yield, the capsules of the Nagasaki and Tsukuba strains were considerably smaller and lighter than those of the Nayoro strain. This is attributable to the fact that flower bud differentiation occurred at an early stage before the achievement of sufficient vegetative growth in the Nagasaki and Tsukuba strains.