Effect of photoperiod on flower bud development of ornamental sunflowers (Helianthus annuus L.)

Abstract

The effect of photoperiod on flower bud development in four ornamental sunflowers in Japan was investigated in an effort to shorten the growing period and to improve commercial cultivation techniques. The number of days from sowing to flower bud development for all cultivars was shortened in the short-day treatment; the same treatment shortened the period between flower bud differentiation to anthesis (FDF) for 'Big Smile' and 'Sunrich Orange', whereas, a long-day treatment hastened FDF for 'Taiyo'. A combination of short/long-day, or day-neutral treatments advanced FDF in 'Valentine'. There were no significant differences in plant height among the cultivars after the onset of flower bud differentiation. The long-day treatment yielded taller plants compared to the other treatments. There was no difference in the flower diameter between the photoperiodic treatments for all cultivars except 'Big Smile'. These results indicate that some cultivars require different day-lengths, depending on their growth stage, i.e., from sowing to flower bud initiation and from flower bud differentiation and development to anthesis. Hence, we recommend that the proper photoperiodic treatment for each growth stage be established for each cultiver.