Variations in flower differentiation period and flowering time in Japanese cherry cultivars

Abstract

Flowering time affects the ornamental value of trees producing cherry blossoms and is important for successful pollination, ensuring high fruit production in cherry trees. We recorded the time to full bloom and inflorescence architecture characteristics of 138 flowering cherry cultivars and two fruiting cherry cultivars grown at Shimane University, Japan (35°30'37”N), and analyzed the relationships among measurement parameters. Late-blooming cultivars tended to form larger inflorescences, with more flowers per cluster. We performed comparative observations of flower differentiation in seven cultivars with different inflorescence architecture characteristics at flowering time. Interestingly, the flower differentiation period was related to neither flowering time nor inflorescence architecture. For example, the very early-blooming cultivar 'Kawazu-zakura', which typically reaches full bloom in mid-March, initiates flower primordia in September and completes flower bud differentiation at the end of September. Flower differentiation occurred later in 'Kawazu-zakura' than in other cultivars. In contrast, the late-blooming cultivar 'Tsukubane', which reaches full bloom in late April, experienced flower bud differentiation in August. In most of the cultivars observed, the number of initiated flower primordia in buds at flower differentiation exceeded the number of flowers in an inflorescence at flowering. Approximately one flower primordium was observed to have degenerated during dormancy or before flowering. Although the factors affecting floral initiation are unknown, a significant difference in the timing of flower differentiation among cultivars may indicate genetic control over the timing of flower differentiation, which is unrelated to bud dormancy regulation.