Flower formation in Primula vulgaris is affected by temperature, photoperiod and daily light integral

Abstract

Primula vulgaris ‘Dania Lemon Yellow’ was grown at photoperiods of 8, 11 and 14 h, daily light integrals (DLIs) of 2, 10 and 18 mol m −2 per day, and temperatures of 8, 12, 16 and 20 °C from transplant (30 days from seeding). Time to flower initiation varied from 28 to 201 days from transplant. Fastest flower initiation as determined by regression analysis occurred at 14 h photoperiod, 11 mol m −2 per day and 13 °C. No correlation between plant size and flower initiation could be identified. At the time of flower initiation, leaf number varied from 6 to 26. Leaf unfolding rate was not affected by photoperiod but increased as a linear function of temperature and DLI (leaves per day=0.01114(°C)+0.007627(DLI). Maximum leaf unfolding rate was 0.36 leaves per day at 20 °C and 18 mol m −2 per day. The length of the longest plant leaf at 8 weeks varied from 4.2 to 9.7 cm. In general, plants at a more advanced flower development stage after 8 weeks had the greater leaf lengths. After 8 weeks of experimental conditions, plants were moved to a common environment (11 h photoperiod, 10 mol m −2 per day and 16 °C). By week 15, the longest plant leaf length varied from 7.4 to 10.5 cm. Although there was a significant trend for longer leaves with a higher initial temperature, leaf size was proportional to overall plant size at all growing conditions. Average number of side shoots decreased from 7 at 8 and 12 °C, to 5 at 16 and 20 °C. The largest number of flowers and buds at termination was more than 100 for plants initially grown at 20 °C and 18 mol m −2 per day. First flower color was recorded after 25–35 days in the common environment for plants initially at 14 h, 10 or 18 mol m −2 per day, and 12 or 16 °C. Less than 35 days was also sufficient for flower color in Primula first grown at 8 °C, 14 h and 10 or 18 mol m −2 per day.