Chapter 9. General Discussion and Conclusion
日日春[Catharanthus roseus (L). G. Don]懸垂性(trailing)品種適合做為吊盆栽培，
近年來極受消費者喜愛，有 Cora Cascade Series (PanAmerican Seed Co., 1997)、
Mediterranean Series (GoldSmith Seeds Co., 2010)及 Boa Series (Floranova Co., 2009) 等品種(陳，2013)。於其他花卉作物中，育種者也常將懸垂或匍匐(prostrate)生長性 狀導入作物商業品種，以提高觀賞性、可應用性、生長勢及抑制雜草生長等優點 (Mirzaie-Nodoushan et al., 1999)。如矮牽牛、金魚草及彩葉草、舞春花等近年來也 推出許多適合做為吊盆栽培的懸垂型品種，可見懸垂型育種目標的重要性。
直立型日日春韌皮纖維屬於次生細胞壁木質素含量低，纖維素含量高之膠質 纖維(gelatinous fiber)(圖 3.3)，且具有反應纖維(reaction fiber)特性，於張力側韌皮 纖維細胞會增大管徑與增厚細胞壁(圖 3.4)，提升支持功能，與瓜皮槭(Acer rufinerve Siebold & Zucc.)張力側韌皮纖維反應相似(Nakagawa et al., 2012)。懸垂型日日春不 具有韌皮纖維，因此支持性較差，枝條易倒伏產生懸垂性狀(第三章)。
日日春懸垂性狀依The International Union for the Protection of New Varieties of Plants 以株型外觀認為是不同表現程度之數量性狀，但本研究依解剖性狀判定商業 品種之直立型與懸垂型兩株型由一對主效基因所控制，且直立型對於懸垂型為顯 性，此基因即為控制韌皮纖維有無之基因，直立型日日春具有韌皮纖維，而懸垂型 日日春不具韌皮纖維，但除了韌皮纖維有無(第四章)，仍有其他微效之因子會影響 到株型性外觀狀表現(第五章)。
莖部組織組成會直接影響株型表現，如藤本植物相較於灌叢植物，莖部組織會 有 更 高 比 例 的 輸 水 組 織 與 較 低 比 例 的 支 持 組 織 ， 且 纖 維 組 織 所 占 比 例 較 低 (Crivellaro et al., 2012)。纖維細胞具有機械支持的功能，而初生纖維細胞主要負責 幼嫩組織的支持功能(Evert, 2006)，無韌皮纖維之懸垂型品種於上盆 25 天主幹彈性 係數(modulus of elasticity，MOE)較低，因此支持性較差而產生懸垂性狀。於藤本
Cascade Polka Dot’枝條更軟更懸垂，具有程度上的差異，而‘Cora Cascade Strawberry’
木質部所佔比例也比‘Cora Cascade Polka Dot’低，因此導致 MOE 下降，枝條更易 彎曲更懸垂，顯示懸垂性狀主要由韌皮纖維有無決定，然而木質部佔莖部比例會影 響到懸垂的程度，是其他影響懸垂性狀的遺傳因子之一(第五章)。
日日春懸垂性狀主要由控制韌皮纖維有無的一對主效基因決定(第四章)，懸垂 型日日春無韌皮纖維，但仍可在韌皮纖維分布位置觀察到長條狀纖維始源細胞。纖 維發育階段依序為細胞分化、細胞延長、累積次生細胞壁最後可能為細胞計畫性凋 亡(Gorshkova et al., 2012)，故推測懸垂型日日春之纖維細胞仍有完成細胞分化與細 胞延長，因此能看到長條狀細胞，但是在合成次生細胞壁時期碰到障礙，無法形成 細胞壁(第三章)。NAC Secondary wall thickening promoting factor 1 (NST1) 與 Secondary wall–associated nac domain protein (SND1)，兩基因為直接控制次生細胞 壁的合成之轉錄因子(Zhong et al., 2007)，且阿拉伯芥(Arabidopsis thaliana L.) nst1/snd1 雙重突變株之纖維細胞形態與懸垂型日日春之纖維始源細胞相似，因此 以AtNST1 與 AtSND1 基因 cDNA 序列做為模板，於日日春轉錄體(Verma et al. 2014) 進行序列比對，顯示於日日春僅有一相似的基因序列，暫名為CrNST1，雖然此基 因 之 CDS (coding DNA secquence) 序 列 於 直 立 型 ‘Vitesse Pink’ 及 懸 垂 型 ‘Cora Cascade Polka Dot’間並無差異，但於懸垂型‘Cora Cascade Polka Dot’莖部表現量略 低，需要進一步確認控制日日春次生細胞壁形成，造成現行商業品種懸垂性狀產生 之基因是否為CrNST1 或其他上游基因(第七章)。
日日春為夏季重要花壇與盆花植物(Ball, 1998)，鮮豔多變的花形與花色是重要 的選育目標，日日春花色多遵循一對基因之遺傳模式，但各基因間常有交感現象 (Kulkarni et al., 2005a; Milo et al., 1985; Simmonds, 1960; Sreevalli et al., 2002)。本研 究指出紫紅色(violet)花瓣對於粉紅色(pink)及白色(white)花瓣為顯性，櫻桃紅 (cherry)花瓣對於粉紅色與杏色(apricot)為顯性，粉紅色花瓣對於杏色花瓣與白色花 瓣為顯性，而杏色花瓣對於白色花瓣為顯性，控制各顏色之基因皆符合一對基因分 離之遺傳模式；深色花瓣對於淺色花瓣為顯性，與前人研究趨勢類似(Kulkarni et al., 2005a；Milo et al., 1985；Simmonds, 1960；Sreevalli et al., 2002)。黃色花冠筒上緣
Sreevalli 等人(2002)觀察之白眼圈性狀類似。中型紅
眼圈性狀相對於小型紅眼圈則由一對顯性基因控制。而花瓣邊緣缺刻且呈波浪狀 之特殊花型性狀由一對隱性基因所控制，且與無花柱性狀連鎖，在重瓣性狀表現之 遺傳背景下會增強花瓣邊緣缺刻性狀表現，於異結合植株就可觀察到花瓣邊緣缺 刻性狀(第六章)。
雄不稔性狀為生產一代商業品種的重要性狀(高，2006)。本研究顯示日日春無 花粉雄不稔性狀由一對隱性基因控制，與Kulkarni 與 Baskaran (2008a)使用甲基磺 酸乙酯(ethylmethanesulphonate, EMS)誘變處理種子獲得無花粉雄不稔之日日春品 系性狀相似，但Kulkarni 等人獲得知突變性狀由兩對隱性基因 ms1 與 ms2 控制，
兩基因皆為隱性同質結合時才表現無花粉雄不稔性狀，本研究使用之材料為一代 雜交商業品種，顯示此基因可能已應用於商業生產上(第六章)。
日日春長期以來缺乏重瓣品種(National Garden Bureau Inc., 2002)，但於 2010 年首度出現花瓣排列緊密、內圈花瓣寬大美觀具商品價值之重瓣品種桃園系列(陳，
2013)，且此性狀由一對隱性基因所控制(Chen et al., 2012)，因此本研究之首要目標 為將日日春重瓣性狀導入懸垂型日日春中，增加日日春可利用性，提升商品價值，
育成重瓣懸垂型日日春新品種(第八章)。
近年來全球暖化，耐熱花卉種類與耐熱品種選育已成為趨勢(Anderson, 2006)，
本研究育成重瓣懸垂日日春新品種，並分析多種具商業價值性狀之遺傳模式，如懸 垂性、花色、雄不稔性狀與花瓣缺刻之特殊花形，期望未來在日日春育種上能有所 參考，使日日春之品種選育更為進步。
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