Moderate variations of day/night temperatures affect flower induction and inflorescence development in Phalaenopsis

We studied the effect of day/night thermal regimes on flower induction and development in Phalaenopsis. The experiment was carried out in Naples in heated glasshouse. Two day/night thermal treatments, 23/21 °C and 19/17 °C, were compared to the standard 21/19 °C recommended regime. The 60-day thermal regimes did not significantly modify the leaf number and final expansion. However, temperature affected the time for the appearance of the flower stem and the subsequent process of flowering. Under the standard regime, flower buds appeared 127 days after the beginning of the treatment and anthesis was completed in 70 days. At higher temperatures, flowering occurred earlier and flower development was faster. In contrast, these two parameters did not change under lower thermal regime. The two thermal treatments under assessment reduced stem and inflorescence length and number of flowers respect to the standard regime. However, lower temperatures promoted the flower stem branching and increased the percentage of plants with two flower stems.