Corydalis speciosa Maxim. is a day-neutral plant with an obligate cold requirement

Abstract

In the modern floricultural industry, there is a market demand for a continuous supply of products, imposing the need for year-round production. The most common and efficient tools for the manipulation of flowering are photoperiodic control and cold treatment. The objective of this study was to identify the cold and daylength requirements for flowering of Korean native biennial Corydalis speciosa Maxim.. The Year 1 experiment was designed to observe the general response of the plant in a greenhouse. Nine-week-old seedlings were treated with 5°C cold for 0, 4, or 8 weeks and then grown under a 9/15-, 12/12-, 14/10-, 16/8-, or 24/0-h photoperiod. The Year 2 experiment aimed to determine the plant response in a more controlled environment using a growth chamber. Seedlings were divided into two stages to examine the age-dependent response. Five-week-old (Stage 1, 5 leaves) or 8-week-old (Stage 2, 10 leaves) seedlings were treated with 5°C cold for 0, 4, 8, or 12 weeks. Plants were grown under a 12/12-h photoperiod because the Year 1 experiment did not show any photoperiodic response. The results from Year 1 demonstrated no photoperiodic response with an obligate cold requirement for flowering. The average flowering percentages were 36% under 4 weeks of cold and 100% under 8 weeks of cold. The Year 2 experiment revealed no significant effect of seedling age on flowering. The average flowering percentages in Year 2 were 81% under 8 weeks of cold and 100% under 12 weeks of cold. The higher flowering rate in Year 1 was presumably because the greenhouse temperature fell below 5°C during the experiment and extended cold exposure. Based on these results, it can be concluded that C. speciosa is a day-neutral plant with an obligate cold requirement of at least 8 weeks.