Effects ofThermal Regime on Growth and Flowering of Lisianthus

Two day/night temperature combinations, 19/25 °C (T-1) and 16/28 °C (T-2), with the same daily mean temperature of 22 °C, were compared on two cultivars of Lisianthus for flower stem production. The experiment was carried out in a growth chamber on plants grown in pots on a peat-based compost. The effect of the treatments on plant growth and development, yield and flower stem quality were studied. The two cultivars showed different light response curves of photosynthesis. Echo plants had a lower light saturation point for photosynthesis compared to Mariachi. The day/night temperature differential did not affect net photosynthesis and leaf chlorophyll content. The number of days from transplanting to flowering was 125 in Echo and 139 in Mariachi. The day/night temperature combination did not influence the flowering time. Cut stem yield was unaffected by the treatments. Flower stems were shorter in Echo with fewer leaves and flowers, and lower leaf area compared to Mariachi. The T-2 regime increased stem length, and reduced stem thickness, the number of flowers and the number of leaves per stem. Nevertheless, the day/night temperature combination did not affect the overall commercial quality of the flower stems. Our results indicate that energy savings can be attained for greenhouse cultivation of Lisianthus by reducing the set point for heating by 3°C and delaying ventilation, without adversely affecting time to flower, yield and flower stem quality.