Effect of temperature on flowering of Rhodohypoxis baurii var. platypetala Nel.

The value of Rhodohypoxis baurii as flowering potted plants has recently been appreciated. There is now a need to study how to control the flowering time. In this study, the growth periodicity of plants grown outdoors was clarified and the effect of temperature on the initiation and development of flower buds was investigated. 1. A corm shows a sympodial branching system, and each unit of the sympodial branch is composed of one foliage leaf and a terminal inflorescence, which bears 1 ti 3 florets. 2. During the growth period from late April to late October, repeated sympodial branching resulted in about 25 inflorescences being initiated. Many of these aborted after the first floret reached the carpel primordia formation stage, and 4-6 inflorescences which passed through the winter at the earlier stage than carpel primordia formation flowered in early June to early July. 3. Corms did not flower when they were moved from outdoors to a greenhouse kept above 20°C on or before January 20. In order to determine the critical temperature and duration for chilling effects, plants were treated with constant temperature of 6, 10, 15 or 20°C at intervals of 2 weeks up to 18 weeks and were then shifted to the greenhouse kept above 20°C. As a result, normal flowering was observed in corms treated at 6°C for more than 12 weeks and at 10°C for more than 16 weeks. 4. After the chilling requirement was fully satisfied, temperatures from 20°C to 30°C advanced flowering. However, some depression in flower size and fading flower colour were observed at 25 and 30°C. Anthesis was hardly influenced by the photoperiod, but the number of emerged leaves decreased in the 8-hour photoperiod.