玉蝶花之扦插繁殖與開花生理

Abstract

玉蝶花(Clerodendrum schmidtii C.B. Clarke)為唇形科大青屬之常綠或落葉灌木。其圓錐花序自然垂墜，白色與紅褐色的花萼與花序軸對比鮮明，可作盆花或景觀植物應用。然玉蝶花自然花期限於冬季，對其繁殖與開花生理資訊尚未明瞭。本研究擬探討適宜玉蝶花扦插繁殖之插穗型式、介質體積含水量、溫度、光週期與生長調節劑對其生長與開花之影響，以供栽培業者參考。 取玉蝶花不帶花芽之綠枝、半硬枝與硬枝部位，剪成15 cm之插穗。綠枝與半硬枝插穗去除所有葉片或僅保留頂部一對成熟展開葉，硬枝本身不帶葉。扦插28天後，綠枝插穗存活率較低，其餘處理全數存活，而僅硬枝插穗全數發根。帶葉之綠枝與半硬枝插穗發根數與最大根長最佳，且根系發育完整。另取其半硬枝部位，裁為5、10、15與20 cm之插穗，各保留頂部一對成熟展開葉。扦插28天後，四處理皆全數存活並發根，且根系長度與發育程度無明顯差異。但15與20 cm插穗之發根數較多， 5 cm插穗僅少量發根。綜合兩扦插試驗，採用15-20 cm長，帶一對成熟展開葉的半硬枝插穗即可達良好繁殖成果。 對玉蝶花施予20%、40%、20/50%與70%之介質體積含水量(volumetric water content, VWC)處理。以20% VWC栽培之玉蝶花生長勢差，嚴重黃化、落葉。且淨光合作用、氣孔導度與蒸散速率最低，而細胞間隙二氧化碳濃度提高，顯示其同時受氣孔與非氣孔因素影響。以40% VWC處理生長旺盛，側枝之數量、長度，及總葉片數與葉面積最高。20/50% VWC處理之生長情形次於40% VWC。而以70% VWC栽培之黃葉與落葉率略低於20% VWC，植株生長亦受限。顯示玉蝶花適合栽培於保持濕潤之環境，乾旱與淹水皆不利生長。 將玉蝶花置於日夜溫為15/13、20/15、25/20、30/25與35/30 ℃的人工氣候室內。植株於15/13 ℃下生長近乎停滯，於試驗末期才產生少量側枝。以20/15 ℃栽培者生長緩慢，側枝數量、長度與葉片數皆低於更高溫之處理。25/20與30/25 ℃最適玉蝶花營養生長。長期置於35/30 ℃下，植株外觀黃化、葉片捲曲，顯示此溫度已構成高溫逆境。玉蝶花以15/13與20/15 ℃處理125天後現蕾，而25/20 ℃處理遲至271.6天後才產生可見花芽。30/25 ℃處理則無花芽產生。於25/20與30/25 ℃處理170天後，將半數植株移至20/15 ℃，其餘植株不移動。兩高溫處理移至20/15 ℃後各於82.2與72.8天時現蕾。 將玉蝶花置於20/15 ℃環境下栽培2、4、6、8、10與12週，再移至自然光照溫室內。隨低溫處理時期延長，玉蝶花之新生花下節數減少，且花序數量增加，顯示充足低溫栽培可促進其花芽形成，並降低花序敗育情形。 以五種光週期栽培玉蝶花，分別為11 h之自然日長(natural daylength, ND)、ND下另以高壓鈉燈(high-pressure sodium lamps, HPS)補充照明(ND with HPS)、以鎢絲燈延長光週期至16 h (day-extension, DE)、以高壓鈉燈延長日長至16 h (ND+HPS DE)與以鎢絲燈行4 h之暗期中斷(night break, NB)。玉蝶花於ND下植株矮小但有少量花序生成。以ND with HPS處理之側枝長度與葉片數較ND為多，且花序發育較快，花序軸長度與花朵數為處理間最高。其餘三處理的植株營養生長旺盛，但不利開花，僅極少量花芽形成，且花序短，花朵數稀少。 以100與200 mg·L-1之GA3，或50、100與150 mg·L-1之巴克素(paclobutrazol)處理玉蝶花之扦插苗，以施用清水為對照組。噴施GA3使側枝與節間延長，但花下節數增加並延後現蕾。經巴克素處理的植株矮小，且高濃度效果更甚。施用巴克素可提升單株花序數量，但花序長度與花朵直徑縮減。而100與150 mg·L-1之巴克素可減少花下節數，顯示其花芽創始提前。 綜上所述，帶一對成熟展開葉、15-20 cm長之半硬枝插穗最適玉蝶花繁殖。保持介質濕潤有利玉蝶花發育，乾旱與淹水皆有害生長。25/20與30/25 ℃為適宜玉蝶花營養生長之溫度範圍，植株於20/15 ℃生長緩慢，但可促進花芽形成。玉蝶花應屬相對短日植物，且高光強度有利生長與花序發育。GA3促進其生長且延後花芽創始，巴克素則矮化植株並加速開花，但濃度過高使生長勢衰弱。

Clerodendrum schmidtii C.B. Clarke (family Lamiacea), an evergreen or deciduous shrub, has been widely used for ornamental decoration or potted plants. The reddish-brown calyx and rachis contrast sharply with white five-lobed petals. However, information on propagation and flowering physiology is presently limited. This study aimed to determine the appropriate cutting type for C. schmidtii propagation, the effect of volumetric water content, temperature, photoperiod, and plant growth regulators on the growth and flowering of C. schmidtii. Softwood, semi-hardwood, and hardwood cuttings taken from non-flowering shoots of C. schmidtii were cut into 15-cm length. Softwood and semi-hardwood cuttings were either defoliated or retained one pair of fully expanded leaves. Hardwood cuttings were leafless. All cuttings survived except for softwood cuttings at 28 days after inserting in the rooting medium. Only hardwood cuttings all rooted. Leafy softwood and semi-hardwood cuttings produced the highest number and length of roots, and the root system well developed. Furthermore, semi-hardwood cuttings were cut into 5, 10, 15, and 20-cm length, retaining one pair of fully expanded leaves on each cutting. All cuttings survived and rooted in each treatment at 28 days after inserting in the rooting medium. There were no significant differences in root length and rooting stage among all treatments. However, 15- and 20-cm-length cuttings produced the most root number while 5-cm-length cuttings had less roots. The results above suggest that 15- to 20-cm-length leafy semi-hardwood cuttings could achieve better propagation results. C. schmidtii were treated with four of volumetric volume water content (20%, 40%, 20/50%, and 70%). Plant treated 20% VWC resulted in poor growth with severe chlorosis and leaf abscission, along with the lowest net photosynthesis rate which was caused by both stomatal and non-stomatal factors. Plants treated 40% VWC were the most vigorous, with the highest number and length of lateral shoots, as well as the most total fully expanded leaf number and leaf area among all treatments. The chlorotic and leaf abscission rate of the 70% VWC treatment was slightly lower than that of 20% VWC, growth were also limited. This suggests that C. schmidtii is suitable for humid environment, and both drought and waterlogging are detrimental. C. schmidtii was placed in phytotron with day/night temperatures of 15/13, 20/15, 25/20, 30/25, and 35/30 ℃. Plants treated 15/13 ℃ were stunted. Plants grown at 20/15 °C produced less and shorter lateral shoots, and less leaves than treated at higher temperatures. 25/20 and 30/25 ℃ were optimal for the vegetative growth of C. schmidtii. Plants treated 35/30 ℃ turned weak and chlorotic in the later stage of the experiment. Flowering occurred within 170 days in the 15/13 and 20/15 ℃ treatments and 271.6 days in the 25/20 ℃ treatment. After 170 days of cultivation at 25/20 and 30/25 ℃, half of the plants from each temperature were transferred to 20/15 ℃ while the remaining plants were not moved. Buds appeared 82.2 and 72.8 days after transfer into 20/15 ℃ from 25/20 and 30/25 ℃ treatments, respectively. No flower buds were produced under 30/25 ℃. C. schmidtii was treated at 20/15 ℃ for 2, 4, 6, 8, 10, and 12 weeks and then transferred to the greenhouse. The number of newly-grown nodes below the first flower bud decreased and inflorescence number increased with increasing duration of 20/15 ℃ treatment, indicating that sufficient low temperature cultivation could promote flower formation. C. schmidtii was cultivated under five photoperiods: natural daylength (ND), ND supplemented with high-pressure sodium lamps (ND with HPS), day-extension with tungsten lamps to 16 h (day-extension, DE), day-extension with HPS to 16 h (ND+HPS DE), and night break with tungsten lamps for 4 h (night break, NB). Plants were short but produced a few inflorescences under ND. Plants under ND with HPS obtained longer lateral shoots and more leaves than ND. The inflorescence developed faster under ND with HPS and obtained the longest rachis length and the highest number of flowers among all treatments. Plants in the other three treatments were vigorous but not suitable to flowering, producing sparse flower buds. Cuttings of C. schmidtii were treated with 100 and 200 mg·L-1 GA3 or 50, 100, and 150 mg·L-1 paclobutrazol (PAZ), while water treatment as control. Spraying C. schmidtii with GA3 elongated lateral shoots and internodes. However, GA3 treatment increased the number of nodes below the first flower bud as well as delayed the days to visible bud. Plants treated with PAZ were significant shorter than the other treatments. High concentrations of PAZ resulted in severely dwarf performance. Application of PAZ promoted the formation of inflorescences but the rachis length and flower diameter reduced. While 100 and 150 mg·L-1 PAZ reduced the number of nodes below the first flower bud, indicating that PBZ could promote flower bud initiation in C. schmidtii.