Investigating the Cold Requirement of Autumn Daffodil (Sternbergia lutea) and the Effect of Bulb Size on Its Growth, Development and Flowering

Autumn daffodil (Sternbergia lutea) is one of bulbous plants from Iran that has potential as an ornamental plant. The understanding and control of dormancy and investigation of cold requirement in this plant are critical for its cultivation This research was conducted to investigate the effects of duration of cold and the size of bulb on growth, development and flowering of autumn daffodil. The experiment was performed as a completely randomized design based on factorial design with two factors: the duration of cold (4 °C) at three levels (20, 40 and 60 days) along with control (without cooling) and three sizes of bulb (small, medium and big) with 3 replications. After applying the cold and planting the bulbs in September 2015, vegetative and reproductive variables were measured. Results indicated that the interaction between cold duration and the different sizes of bulbs had a significant effect on most of the measured vegetative and reproductive characteristics. By applying the cold treatment, the numbers of days to sprouting and two, four and five leaves stages were increased. The highest amounts of leaf area, fresh and dry weights were obtained with big bulb and 40 days of bulb cooling. Parameters such as volume, length, and number, fresh and dry weights of bulb roots were higher in bulbs that had been kept a way from cooling. The highest of flowering percentage, flower longevity on the bush, flowering stem height, fresh and dry weights were obtained in big bulbs with 20 days of bulb cooling. Flowering was not observed in 40 and 60 days of bulb cooling. According to the results of this research, it can be concluded that autumn daffodil bulb has a little cold requirement or the cold requirement is not obligatory. According to the results obtained, the treatment of 20 days of cooling with the big size of bulb is recommended although further research is needed to investigate the dormancy status of the bulb in terms of physiological, biochemical and molecular aspects.