The effect of photoperiod and temperature on reproductive development of Cape Daisy ( Osteospermum jucundum cv. ‘Pink Whirls’)

Abstract

The flowering responses to photoperiod and vernalising temperatures were examined in Cape Daisy ( Osteospermum jucundum cv. ‘Pink Whirls’). At a day/night temperature of 18/12 °C, flowering occurred 10 days earlier (60 days) when plants were grown under glasshouse conditions at a photoperiod of 16 h day −1 compared with 8 h day −1. Photoperiod had no significant effect on the number of side-shoots produced. Plants grown at 8 h day −1 attained half the height of those grown at 16 h day −1. A reciprocal transfer experiment between plants maintained in growth cabinets at 12 and 22 °C was used to investigate the time when (and if) the plants were sensitive to cold. Plants transferred to and from each cabinet on seven weekly occasions indicated that Osteospermum had a requirement for cold prior to flowering. Plants maintained at warm temperatures (22 °C) were still vegetative 120 days after planting, whilst plants grown at 12 °C flowered after 81 days. Plants required at least 2 weeks of cold temperatures to induce flowering. Following this, flower development rate was increased by warmer temperature. Flowers took 38 days longer to develop at 12 °C than those maintained at 22 °C. Leaf number initiated before the flower was constant in plants exposed to 12 °C for at least the first 2 weeks after planting; however, all plants maintained initially at 22 °C had higher leaf numbers. Owing to delayed flower initiation, progressively longer durations of warm temperatures led to progressively higher final leaf numbers. Vernalising treatments (12 °C) had no effect on branch number. Final flower size declined when the plants matured at 22 °C.