Abstract
Exposing seedlings of Eustoma and Delphinium to high temperature induces rosetting. Therefore, in the cultivation for earlier flowering of these species, the utilization of a cooling system during raising of seedlings in the summer seems to be necessary in order to prevent rosetting. Eustoma and Delphinium seeds were sown in a greenhouse on 17 May. The seedlings were planted in 7.5 cm pots on 17 July. These were transferred under the spot-cooling condition or outdoors on 19 July. The daily mean temperature under the spot-cooling condition was kept less than 20°C, 10°C lower than that of outdoors where the control plants were placed. The potted plants were transplanted on the soil beds in a plastic house on 18 September in Eustoma, on 14 October in Delphinium. They were exposed to a photoperiod of a 16-h day and maintained above 10°C from the end of October. As a result, Eustoma seedlings raised under the spot-cooling condition did not show any rosetting and produced floweres of high quality in late March, 2 months earlier than those grown outdoors. As for Delphinium, 48% of control plants raised outdoors showed flower stalk development of 10-20 cm in length during the summer season. Almost all of them subsequently died. The rest of the live plants showed rosetting after transplanting and flowered in late April, while none of the plants under the spot-cooling condition showed either flowering during the summer season or rosetting after transplanting. These plants flowered with an infloresence of high quality and long flower stems in mid January.
