Temperature affects flower initiation and development rate of impatiens, petunia, and viola

Impatiens walleriana Hook f. ('Super Elfin Lipstick'), Petunia × hybrida Vilm. ('Avalanche Pink' 'Dreams Rose', 'Wave Purple'), and Viola × wittrockiana Gams. ('Colossus Yellow Blotch', 'Crystal Bowl Supreme Yellow', 'Delta Pure White', 'Sorbet Blackberry Cream') were grown under different temperature regimes to quantify the impact of temperature on flower initiation and development rate. Ten seedlings of each cultivar were placed in four controlled environment chambers maintained at constant 12, 16, 20, or 24 °C with an 18 hr photoperiod (inductive; 350 μmol m-2 s-1). Data were collected on days to first open flower (DTF), leaf number below the first open flower (LN), flower number (FN), and branch number (BN) when the first flower opened on each plant. DTF decreased from 112 ± 2 to 45 ± 1 d for Petunia 'Wave Purple' and from 68 ± 1 to 45 ± 1 d for Viola 'Sorbet Blackberry Cream' as temperature increased from 12 to 24 °C. The sensitivity of DTF to average daily temperature (ADT) was most obvious when assessing the impact of decreasing temperature 1 °C. For example, when temperature was decreased 1 °C, DTF of Impatiens 'Super Elfin Lipstick', Petunia 'Avalanche Pink', and Viola 'Colossus Yellow Blotch' increased 3, 4, and 3 days respectively. DTF decreased from 72 ± 2 to 47 ± 1 d for Impatiens 'Super Elfin Lipstick' as temperature increased from 16 to 24 °C. Impatiens plants grown at 12 °C died. LN decreased for all plants as temperature increased. For instance, as temperature increased from 12 to 24 °C LN of P. × hybrida 'Dreams Rose' and V. × wittrockiana 'Crystal Bowl Supreme Yellow' decreased by 6 and 4, respectively. Plant quality (FN, BN) of P. × hybrida decreased with increasing temperature, while FN of I. walleriana increased and plant quality of V. × wittrockiana was unaffected by increasing temperature.