溫度對沙漠玫瑰光合作用、葉片生理、開花及花粉萌發之影響

Abstract

沙漠玫瑰屬(Adenium)為夾竹桃科(Apocynaceae)的多年生花卉，觀賞部位為膨大莖幹與花朵，具有不同單瓣及重瓣花型，常作為盆花或景觀作物利用。目前仍缺乏沙漠玫瑰光合作用、開花生理及花粉特性之研究，故欲探討溫度對沙漠玫瑰生長、開花及花粉萌發之影響。另探討單瓣及重瓣沙漠玫瑰其柱頭可受性及花粉萌發習性，以供育種者可加速選育重瓣花之品種。 沙漠玫瑰栽培於光度1007 µmol·m-2·s-1，平均日長11.1 h，溫度32.3℃時，淨光合作用速率隨光度增加而上升，於冬季測量得知其光飽和點約為300 μmol∙m−2∙s−1，淨光合作用速率為9.9 μmol∙m−2∙s−1，光度提升不影響蒸散作用與氣孔導度，僅細胞間隙二氧化碳濃度隨光度增加而下降。其光反應曲線顯示其光補償點為24.6 μmol∙m−2∙s−1。二氧化碳濃度自0提升至800 μL∙L-1，使淨光合作用速率隨之增加，且細胞間隙二氧化碳濃度亦提升。當VPD固定為1.2 kPa時，沙漠玫瑰光合作用適溫為22-28℃。在1.0-2.3 kPa VPD區間，沙漠玫瑰之淨光合作用速率、氣孔導度及細胞間隙二氧化碳濃度對VPD變化不敏感。 除去頂芽之沙漠玫瑰在每日平均最大光強度為1520 µmol·m-2·s-1下，以日夜溫25/20、30/25以及35/30℃處理所有植株皆開花，且花下葉片數無顯著差異，但30/25以及35/30℃處理顯著降低現蕾天數及開花天數，分別於，其中以30/25℃有最高開花率。日夜溫15/13及20/15℃則易發生寒害，以15/13℃處理顯著降低光系統Ⅱ最大光子利用效率(maximum quantum efficiency of photosystem Ⅱ photochemistry, Fv/Fm)、非光化學淬熄係數(non-photochemical quenching coefficient, qN)及SPAD-502讀值。觀察不同日夜溫處理對頂花序帶1.5 cm花苞的沙漠玫瑰之影響，結果日夜溫降低，花芽發育至到花天數及花朵壽命顯著增加。日夜溫15/13及20/15℃則在處理17天後消蕾，所有試驗植株皆無開花。另觀察不同日夜溫對原生種單瓣、半重瓣‘小燕子’及重瓣‘石榴裙’花粉萌發之影響，結果顯示三品種沙漠玫瑰於30/25℃培育有最高花粉萌發率。 沙漠玫瑰依花瓣輪數可分為單瓣‘黑色月光’(一輪花瓣)、半重瓣‘小燕子’(兩輪花瓣)及重瓣‘石榴裙’(三輪花瓣)。半重瓣具有兩輪花冠筒，一為萼片瓣化之花冠筒，可見萼片遺跡，且花冠筒可完整分離為五瓣，另一輪為正常花瓣，第四輪為正常雄蕊，可取得可稔花粉，第五輪為正常雌蕊；重瓣花朵具有三輪花冠筒，三輪皆為完整花冠筒，第五輪雄蕊之花藥常畸形，若花藥發生畸形則無法取得花粉，若正常發育則為可稔花粉，第六輪為雌蕊正常無畸形。 將單瓣‘黑色月光’、半重瓣‘小燕子’及重瓣‘石榴裙’依照花發育階段分為6個階段，分別為花瓣尚未突出萼片、花瓣突出部位與萼片等長、花瓣突出部位與萼片2：1、花瓣突出部位與萼片3：1、花朵開放前最大長度及完全開放花朵，分別調查各階段之花器結構，結果顯示三品種中以完全開放花朵有最高柱頭可受性、花粉活力及花粉萌發率，且半重瓣及重瓣者於完全開放階段花朵才可取得花粉。 三品種沙漠玫瑰皆以添加10%蔗糖之處理其花粉萌發率最高。取三種花型沙漠玫瑰花粉以不同水浴溫度處理後，將最低與最高萌發率溫度與更高水浴溫度之數據行直線迴歸後，計算兩直線迴歸線之交叉點，可得花粉萌發之基礎溫度、最適溫度及最高溫度。單瓣‘黑色月光’之花粉萌發基礎溫度為8.8℃，最適溫度為26.6℃，最高萌發溫度為41.9℃；半重瓣‘小燕子’之花粉萌發基礎溫度為11.6℃，最適溫度為30.7℃，最高萌發溫度為42.8℃；重瓣‘石榴裙’之花粉萌發基礎溫度為11.6℃，最適溫度為27.0℃，最高萌發溫度為42.1℃。 取單瓣‘黑色月光’、半重瓣‘小燕子’及重瓣‘石榴裙’新鮮花粉於室溫乾燥一週後，放入不同溫度貯藏，結果顯示單瓣‘黑色月光’以4℃貯藏花粉萌發率可維持2週，至第4週則顯著降低；半重瓣‘小燕子’以4℃貯藏花粉萌發率可維持至第4週，至第8週才有明顯降低；重瓣‘石榴裙’以-20℃貯藏1週可有最佳花粉萌發，其他溫度處理及貯藏時間超過1週皆顯著降低花粉萌發率。 以單瓣、半重瓣及重瓣沙漠玫瑰進行自交及正反交，結果顯示9種授粉組合皆可成功結實並獲得種子，雜交後代亦可順利萌發，待日後觀察是否可將重瓣基因導入子代。

The desert rose (Adenium obesum), belonging to the Apocynaceae family, is a perennial flowering plant. Its prominent features include enlarged stem and showy flowers, which have various single- and double-flowered forms, and are often utilized as potted ornamental plants or in landscaping. Currently, there is still a lack of research on the photosynthetic characteristics of the desert rose. Temperature is likely a primary factor facilitating growth of desert rose based on response of gas exchange parameters towards various environmental factors. Therefore, further exploration into the effects of temperature on the growth, flowering, and pollen germination of the desert rose is necessary. To expedite and ensure the breeding process, it is essential to explore the stigma receptivity and pollen characteristics of both single- and double-flowered desert rose. This research would aid breeders in accelerating and ensuring the smooth progression of the breeding procedures. The net photosynthetic rate (Pn) increases with rising light intensity. The net photosynthetic rate reached saturation at light intensity of 300 μmol∙m−2∙s−1. Light compensation point was estimated as 24.6 μmol∙m−2∙s−1. With light intensity increases further, there was no significant change observed in transpiration rates (E) or stomatal conductance (gs), but the intercellular CO2 concentration (Ci) decreased as light intensity increased. As the CO2 concentration increased from 0 to 800 μL∙L-1, the Pn and Ci of the desert rose increased. When the vapor pressure deficit (VPD) was fixed at 1.2 kPa, the optimal temperature range for photosynthesis in desert rose is between 22-28°C. The desert rose, pinched before treatments, flowered at day/night temperatures of 25/20°C, 30/25°C, and 35/30°C. The number of leaves below flowers showed no significant difference among treatments. However, at 30/25°C and 35/30°C, there was a notable reduction in the time to visible buds and anthesis, and the 30/25°C treatment had the greatest flowering rate. Under 15/13 and 20/15°C, desert rose exhibited chilling symptoms and lower Fv/Fm, qN and SPAD-502 values. Plants with 1.5 cm-longed flower buds were treated with various day/night temperatures. All plants under the 25/20°C, 30/25°C, and 35/30°C treatments exhibited flowered. As temperature decreased, number of days to flowering and the lifespan of flowers significantly increased. However, plants at 15/13°C and 20/15°C exhibited bud abortion after 17 days. The single-flowered Adenium obesum, semi-double-flowered ‘Little Swallow’, and doubled-flowered ‘Entrancing’ all had the greatest pollen germination with their flower buds developed under 30/25°C. Desert rose could be categorized as single-flowered (one corolla whorl, Type 0), semi-doubled-flowered (two corolla whorl, Type 1), or doubled-flowered (three corolla whorl, Type 2). Type 1 could be further classified as 1-A, 1-B, and 1-C. Type 1-A flower had two complete corolla, suggesting the repetition of the petal organ; Type 1-B had a visible remnant of sepals in one whorl of the corolla; Type 1-C possessed two whorls of corolla while simultaneously having normal and petaloid stamen. Floral development in desert rose was divided into 6 stages as corolla not protruding out of sepal tube, corolla length was the same as sepal tube, corolla length was twice the sepal tube, corolla length was three times of sepal tube, maximal corolla length, and anthesis. Results showed that all cultivars had the best stigma receptivity and highest pollen germination rate. All desert rose cultivars tested exhibited the highest pollen germination when incubated with the BK medium containing 10% sucrose. The base (Tb), optimum (To) and maximal (Tm) temperature for pollen germination in single-flowered ''Black Moon Light'' was estimated to be 8.8, 26.6 and 41.9℃, respectively. While Tb, To, Tm for pollen germination for semi-double-flowered ‘Little Swallow’ were 11.6, 30.7 and 42.8℃, and 11.6, 27.0 and 42.1℃ for double-flowered ‘Entrancing’. Pollen of desert rose cultivars tested were harvested and dehydrated at room temperature for 1 week followed by various storage treatments. Pollen of single-flowered ‘Black Moon Light’ and semi-double-flowered ‘Little Swallow’ could only be stored at 4℃ for 1-2 weeks. Pollen of double-flowered ‘Entrancing’ could only be stored at -20℃ for 1 week and the germination rate of stored pollen decreased significantly with increased storage duration. Self-pollination and reciprocal crosses were made with single-, semi-double- and double-flowered desert rose. Results showed that all nine pollination combinations resulted in successful fruiting and seed production. The hybrid offspring also germinated successfully, indicating that desert rose possess self-compatibility.