Effect of Photoperiod on Flowering and Growth of Ornamental Sunflower Cultivars

Abstract

Effect of photoperiod on flowering response and growth of 18 ornamental sunflower cultivars was evaluated. Plants were grown in a glasshouse under 16 h long day (LD) or 11.5 h short day (SD) conditions. In 12 of the cultivars tested (66.7%), visible flower bud stage was significantly earlier under the SD than under the LD. All of the cultivars flowered under both the SD and the LD conditions. However, 16 cultivars (88.9%) had a quantitative SD response, that is, their flowering was significantly delayed under LD. Delay of flowering under LD was variable among the cultivars, and was 14 days or greater in 11 of them. Photoperiod had no effect on flowering of ‘Jamboree’. This cultivar behaved clearly as a day-neutral (DN) plant. The cultivar ‘Sailor Moon’ showed a LD response; its flowering was earlier under LD. In 14 of the cultivars showing a SD response, photoperiod also influenced plant height, resulting in taller plants under LD. In the most of cultivars there was no effect of photoperiod on flower and stem diameters.