Environmental Factors Affecting Rosette Formation of Elatum Hybrids of Delphinium

Abstract

To determine environmental factors involved in rosette formation of Elatum hybrids of Delphinium, bolting behavior in response to temperatures, photoperiods, and light intensities was investigated. Seedlings rosetted under a natural 10-12 hr photoperiod during winter at 22°C. Seedlings subjected to 25/20°C (day/night) for 40 days just after germination formed rosettes after they were transferred to below 20/15°C, whereas they bolted quickly when they were kept at the continuously high temperature. A high percentage of seedlings bolted when they were transferred to a greenhouse kept above 18°C in early October, but those kept at a minimum temperature of 10°C formed rosettes. This rosette formation was also accelerated by exposing seedlings to 50% shading. We conclude that short days induce rosette formation in Elatum hybrids of Delphinium and that cool temperature accelerated it. Exposure of seedlings to high temperatures during the early seedling stage and/or low light intensity after planting also enhanced rosette formation.