Effect of Temperature on Flowering on Lycoris squamigera Maxim. and L. radiata Herb.

Abstract

The effect of temperatures during different developmental stages on the time of initiation and development of flower buds of L. squamigera and L. radiata which blooms in mid-August and late September, respectively, was studied.
1. Flower initiation occurred between 10° and 30°C, but the optimum temperature for flower initiation and subsequent differentiation to stage 8 of floral organs was 30°C in both species.
2. The development of flower buds, from stage 8 of complete carpel differentiation to stage 12, when pollen become mature and functional, progressed more rapidly at 20° and 25°C than it did at 30°C. The time intervals for flower development from stage 8 to 12 at optimum temperatures were 4 and 8 weeks for L. squamigera and L. radiata, respectively.
3. The range between 20° and 25°C was also optimum for the development of flower buds from stage 12 to anthesis. Anthesis in L. squamigera and L. radiata at 30°C was delayed about 10 and 30d, respectively, as compared to that at 20° or 25°C. All L. squamigera plants held between 10° and 30°C flowered, but only those of L. radiata held between 20° and 30°C flowered.
4. Although plants of L. radiata kept at 20°C after carpel formation flowered normally, those which were transferred to 30°C for 3 to 5 weeks and then returned to 20°C bloomed 1 month earlier.
5. Bulbs of L. radiata exposed to 15°C for 6 weeks and transferred to 20°C at carpel initiation (stage 8 to 9) flowered normally; whereas, those transferred to 15°C for 2 weeks at or after pollen formation (stage 9-12) and returned to 20°C bore blasted flowers.
6. These results demonstrate that plants of L. squamigera and L. radiata bloom at different times under natural conditions, after carpel primordium is completed, as a response to ambient temperatures which govern the rates of subsequent floral development.