Understanding bulb dormancy while examining temperature-related requirements and photoperiod are essential for successful commercialization and the greenhouse forcing of autumn daffodil (Sternbergia lutea). In this study, autumn daffodil bulbs were stored at 5, 15 and 25 °C for one month. Then, one group of bulbs were evaluated in terms of biochemical characteristics in three parts of each bulb (scale, central bud and basal plate). A second group of bulbs were planted in a greenhouse for a separate experiment to study the effects of different photoperiods (short, moderate and long) on morphological traits. The heat map of treatments in the first experiment revealed that the bulb storage temperatures of 15 °C and 25 °C had somewhat similar effects on all three parts of the bulb but, conversely, 5 °C had discrete effects. The 5 °C resulted in higher contents of proline in the scale, along with more H2O2 and malondialdehyde (MDA) in the basal plate. The highest activity of peroxidase (POD) and superoxide dismutase (SOD) were observed at 15 °C in the basal plate and at 5 °C in the central bud, respectively. In the second experiment, the time required for bulb sprouting and time to flowering were as follows: 5 °C > 25 °C > 15 °C. The heat map analysis indicated that temperature played a more substantial role than what photoperiod did in shaping the morphological traits. The interaction between 15 °C and the moderate photoperiod led to the highest value of most vegetative traits and of flowering percentage (70%). Therefore, this treatment can be considered as optimum for breaking relative bulb dormancy and to succeed better in growth and flowering.
