Improvement of Eustoma grandiflorum (Raf.) Shinn. cut flower quality for early-autumn shipping with long-day treatment using light sources that delay flower bud formation

Eustoma grandiflorum (Rat) Shinn. was subjected to long-day treatment using four types of light sources with a high red (R; 660 30 nm) to far-red (FR; 730 30 nm) light ratio to improve cut flower quality for early-autumn shipping. The R:FR ratios of a red-light fluorescent lamp, a color fluorescent lamp (R-type), a bulb-type red-light fluorescent lamp, and a bulb-type daylight fluorescent lamp were 62.0, 100.0, 8.8, and 8.5, respectively. As a control, plants were grown under ambient daylight. Flower budding of 'Double Pink' seedlings, planted on July I I and treated with night-break treatment from planting to budding using these four light sources, was delayed 2-5 days compared with the control. Night-break treatment using each light source increased the number of nodes on the main stem, number of lateral branches, and number of flower buds, and increased the cut flower length of plants at anthesis of the first floret, compared with the control. Three cultivars were treated with night break using a color fluorescent lamp (R-type) and a bulb-type red-light fluorescent lamp. Although these two light sources did not delay the flowering of 'King of Snow' compared with the control, the mean flowering date of 'Double Pink' and 'Piccolosa Snow' under both light sources was 3-6 days later than that of the control. These light sources increased the number of nodes of the main stem, and increased the stem length and cut flower length compared with the control in each cultivar. As the most practical application, the bulb-type red-light fluorescent lamp was used for long-day treatment of 'Double Pink' under four lighting periods: pre-dawn lighting for 6 h, end-of-day lighting for 6 h, all-night lighting, and night break for 6 h during the night. All-night lighting delayed flowering more than the other treatments. Cut flower length of the plants at anthesis of the first floret was longest in the pre-dawn lighting treatment. We concluded that long-day treatment using a bulb-type red-light fluorescent lamp from 0:00 to 6:00 just after planting until flower budding is most effective to improve cut flower quality for early-autumn shipping of Eustoma cultivars.