溫度及光週對非洲芙蓉開花之影響

Effects of Temperature and Photoperiod on Flowering in Pinkball Dombeya wallichii)

非洲芙蓉[Dombeya wallichii (Lindl.) K.Schum.]為錦葵科之觀賞花木，應用於盆花或景觀布置深受歡迎，然而其在臺灣及其他亞熱帶地區的自然花期局限於12-3月，因此本研究探討溫度及光週對非洲芙蓉開花之影響。於5月初取高度20 cm，帶兩片葉之扦插苗，置於日/夜溫為15/13、20/15、25/20、30/25或35/20℃的人工氣候室。結果顯示隨溫度由25/20降低至15/13℃使非洲芙蓉始花節位遞減，於15/13-25/20℃處理112-119天後可觀察到花芽，而30/25及35/30℃處理182天後仍未產生花芽。將原本於30/25與35/30℃處理18週之半數植株移入15/13℃涼溫中，結果顯示植株移入15/13℃者有花芽形成，持續於高溫者無花芽。另於12月初將具花芽之植株進行溫度對花芽發育之影響，結果顯示25/20℃處理者可見花序數最多，開花最早，15/13及20/15℃處理者花序發育緩慢，30/25℃不利花芽發育，處理50天後有38.6%消蕾。非洲芙蓉的花芽發育基礎溫度約為1.6-1.8℃，自花芽直徑2.1±0.1 cm發育到花萼顯色及開花階段分別約需441±45℃d及600±44℃d。於8月中旬取綠枝扦插苗置於24/14℃，以照光8 h的環境(300μmol·m-2·s-1 photosynthetic photon flux density, PPFD)經7、14、21、28或35天後，移入16 h長日環境(150μmol·m-2·s-1 PPFD)。結果顯示隨著8 h處理天數增多，植株之始花節位及新長之節間長減少，而花芽數目及花芽直徑則增加。

Dombeya wallichii (Lindl.) K. Schum. (Malvaceae) is a popular woody ornamental as potted flowers and in landscaping. However, the natural flowering duration is limited between December and March in Taiwan and other subtropical areas. Effects of temperature and photoperiod on flowering were examined in this study. Single-stemmed Dombeya plants from cutting propagation with two expanded leaves and 20 cm height were grown in phytotrons at 15/13, 20/15, 25/20, 30/25 or 35/30℃in May. Results showed that nodes below the first flower bud decreased when temperature lowered from 25/20 to 15/13℃. Flower buds were first observed at 112-119 days after grown at 15/13 to 25/20℃, while plants at 30/25 and 35/30℃did not produce any visible flower bud at 182 days after treatments. The apparent vegetative plants grown at 30/25 and 35/30℃for 18 weeks were then divided and halves were transferred to 15/13°C. Results showed that 15/13°C treatment lead to flower bud formation, while those kept at high temperatures did not produce any flower bud. In another study, plants with flower buds were moved into phytotrons in December. Results showed that plants grown at 25/20°C flowered first with the greatest number of visible inflorescences, whereas plants at 15/13 and 20/15℃grew slowly and those at 30/25°C showed 38.6% flower bud blasting at 50 days after treatments. The base temperature for flower bud development was estimated ca.1.6-1.8℃, and the thermal times required from 2.1±0.1 cm flower bud to calyx visibility and anthesis were estimated as 441±45℃d and 600±44℃d, respectively. Rooted softwood cuttings were placed at 24/14°C and received 7, 14, 21, 28, and 35 days of 8-h photoperiod (300μmol·m-2·s-1 photosynthetic photon flux density, PPFD) and then transferred to 16-h photoperiod (150μmol·m-2·s-1 PPFD). Results showed that node number when first flowering and length of newly-formed internode decreased, while number and diameter of flower buds increased with increasing duration of 8-h photoperiod.