Selection of Summer-to-autumn-flowering Small-flowered Spray-type Chrysanthemums for Fine Control of Flowering Using Light Culture

Abstract

We developed a method to select summer-to-autumn-flowering small-flowered chrysanthemum cultivars suitable for the fine control of flowering using light culture. Budding under non-inductive night-break conditions was investigated from March to May. 'Subaru' and 'Sei-chigusa' showed no budding under night-break conditions during experimental periods. However, 'Sei-shimanami' showed a seasonal change in budding under night-break conditions, being late in March and very early in May. This indicated that premature budding under night-break conditions may occur more in late summer to autumn than in early summer. Therefore, we selected summer-to-autumn-flowering small-flowered chrysanthemum cultivars whose flower initiation is inhibited by night-break until cropping on the day of the autumn equinox in September in Okayama Prefecture. Several cultivars that showed later budding than the summer-to-autumn-flowering standard-type chrysanthemum cultivar 'Sei-un' used in light culture were selected for the fine control of flowering using light culture. We confirmed and evaluated the utility of these selected cultivars for flowering control using light culture in Fukushima, Akita and Ibaraki Prefectures. Although the flowering time of the selected cultivars varied among prefectures under natural daylength conditions, fine control of the flowering time was established using light culture. These results show that the method developed in this study is useful for selecting summer-toautumn-flowering small-flowered chrysanthemum cultivars suitable for the fine control of flowering by using light culture.Key Words：long-day leaf number, night-break, photoperiodic response, retarding culture, short-day plant

Delay of Flowering at High Temperature in Chrysanthemum: Duration of Darkness and Transitions in Lighting Determine Daily Peak Heat Sensitivity

“…A three-hour heat pulse at 30°C was applied daily at 10-13 or 13-16 h after L-off. 'Sei-shiraito' is a summer-to-autumn-flowering C. morifolium cultivar that can flower under a shorter period of darkness than NIFS-3 (Mori et al, 2017). Heat pulse treatments of 'Sei-shiraito' were performed under 10 h-D/14 h-L or 15 h-D/9 h-L conditions (Fig.…”