Effects of Intermittent Low Temperature Storage Duration and Cycle on the Growth and Flowering of Eustoma (Eustoma grandiflorum L.) Seedlings Raised in the Summer

In the present study, we evaluated the effects of intermittent low temperature storage (ILTS) following cold imbibition of Eustoma seeds as a low-cost method. The objective of this study was to investigate the effects of the total number of cold storage days and the lengths of ILTS cycles for seedlings on the subsequent growth and flowering of three cultivars with different susceptibilities to rosetting: ‘Nancy’, ‘Exe Lavender’, and ‘Bolero White’. Before sowing, the seeds were imbibed with water at 10°C under a dark condition for 35 days. A cycle of 6D/6D (6 days in a refrigerator kept at 10°C in the dark/6 days in a greenhouse kept at a high ambient temperature) was repeated 0, 1, 2, 3, 4, and 5 times to attain 0, 6, 12, 18, 24, and 30 days of cold storage (DCS), respectively. Using a cycle of 6D/6D at least one time (6 DCS) increased the bolting and flowering percentages and accelerated the bolting date by 6–10 days and the flowering date by 4–9 days in ‘Nancy’, a high-rosetting cultivar. The percentage of harvesting was above 80% only in seedlings subjected to 24 and 30 DCS in ILTS. In addition, under equal 30 DCS of ILTS, cycles of 3D/3D × 10 times, 6D/6D × 5 times, and 15D/15D × 2 times were investigated by exposing the seedlings to a high ambient temperature for 3, 6, and 15 days and then transferring them to a refrigerator (10°C) for 3, 6, and 15 days, respectively. ILTS cycles of 3D/3D and 6D/6D resulted in earlier bolting and flowering dates than cycles of 15D/15D. The cycle of 15D/15D resulted in a lower percentage of marketable harvesting and an increased number of nodes to the first flower. These results suggest that applying ILTS with a cycle of 6D/6D at least four times can be an efficient method to promote the bolting and flowering of Eustoma without applying air conditioning to the entire greenhouse.