Variation of Dormancy and Early Flowering Ability in Lilium longiflorum and L. formosanum Populations in the Ryukyu Archipelago and Taiwan

Variations in the dormancy and early flowering ability of seedlings of four populations of Lilium longiflorum, Yaku Shima (LYA), Kikai Jima (LKI), and Ishigaki Jima (LIS) in the Ryukyu Archipelago, Japan and Pitouchiao (LPI), Taiwan, and two populations of L. formosanum, Wulai (FWU), Taiwan and a domesticated Fukuoka population (FFU), Japan were investigated. Seedlings of each population were grown at 15°C for five months. They were then transplanted into an experimental open field for two years or at 15, 20, 25, and 30°C under natural day length for 22 weeks. In the field experiments, FWU, FFU, and LPI populations continued to develop new leaves even at >30°C. Flowering percentage for FFU and LPI was 90% and 19.7%, respectively. Leaf development of LIS, LKI, and LYA was completely arrested from early June in both years, and the flowering percentages were 28, 25, and, 10 in the second year, respectively. Under controlled temperature conditions, LKI and LYA populations produced new leaves only at 15°C. FFU and LPI continued growing at 25 and 30°C, whereas the other populations did not grow. FFU significantly produced the heaviest leaves and bulbs and the highest number of scales per bulb at any temperature. The results showed that high temperature induces bulb dormancy in northern L. longiflorum. Strong correlation with the early flowering ability and bulb dormancy was also found. It seems that the early flowering ability of L. formosanum is largely dependent on the lack or reduction of bulb dormancy after adaptation to the local southern climate. The latitudinal variation of this trait demonstrated the geographic gradient during species habituation in the Ryukyu Archipelago.