Effects of Hydrogen Cyanamide Spraying on Floral Development and Blossom Characteristic Form in ‘Kawazu-zakura’ (Prunus lannesiana Wils.) Cherry Blossom Trees

We investigated the relationship of temperature with the flowering period of Prunus lannesiana Wils.'Kawazu-zakura'cherry blossom trees planted in the river embankment. We also studied the acceleration of flowering owing to the ef-fect of hydrogen cyanamide (H2CN2) spraying for improvement of ornamental value, pro-motion of tourism, and production of cut flowers. In 2011, 20, 50, and 100 % blooming was reported by February 16, February 21, and March 2, respectively. In 2012, 20, 50, and 100 % blooming was reported by February 23, February 26, and March 9, respec-tively. There was a difference of 5-7 days in the flowering date between 2011 and 2012. The cumulative temperature with the number of days between "green tip" and "full bloom" in the floral bud development process was within 234-259 degree days, and it re-mained fairly constant over all years evaluated. However, the average temperature from early November to mid-November, before the start of flower bud development, was 2.6-3.8 ℃ higher in 2012 than in 2011. It was suggested that the temperature after flower bud development initiation, in addition to the temperature during endodormancy termination, greatly affects the flowering period of'Kawazu-zakura'. After spraying of H2CN2, the branches were cut and transferred to a thermostatic chamber, where flower bud development started earlier by 35, 32, and 19 days at 5, 10, and 15 ℃, respectively, than in the untreated plot. However, there was no difference in flower bud developmental rate. Thus, flowering was accelerated by this treatment, mainly due to early development of flower buds. No effects of H2CN2 spraying on floral diameter and petal color were observed.