夏蓳之花朵性狀遺傳與遠緣雜交障礙

Abstract

夏蓳(Torenia fournieri Linden)為倒地蜈蚣屬植物，是臺灣春夏季之重要草花，且臺灣有四個同屬的原生種可為育種親本，供應可能之市場所需。目前仍缺乏臺灣原生種與商業品種雜交後的相關研究，因此本研究以夏蓳、母丁香(T. flava Buch.-Ham. ex Benth.)、倒地蜈蚣(T. concolor Lindl.)及毛葉蝴蝶草(T. benthamiana Hance)為材料進行自交及種間雜交，並觀察雜交花粉管於花柱內生長之情形、雜交胚乳及胚之生長發育、雜交果莢之生長與雜交種子數量，以瞭解倒地蜈蚣屬種間雜交時是否有不親和及其發生之授粉受精階段；其次，以夏蓳小丑品種為種子親與黃花夏蓳‘Suzie Wong’雜交，並調查後代性狀之遺傳。 在溫室環境下，母丁香自交4小時後可觀察到花柱中有花粉管螢光，並持續延伸至子房中，而取夏蓳‘Clown Blue’花粉與母丁香雜交，授粉4小時後亦可觀察到花粉管螢光且持續延伸至子房中，然螢光亮度較弱。取夏蓳‘Clown Rose’花粉與母丁香雜交，授粉後4小時則未能清楚觀察到花粉管螢光。取倒地蜈蚣花粉與夏蓳‘Clown Blue’及‘Clown White Blush’雜交，授粉4小時後可觀察到花柱中有花粉管螢光，而取毛葉蝴蝶草進行雜交時，授粉4小時後僅能觀察到花柱中有少量且微弱的花粉管螢光。各雜交組合可觀察到花粉管螢光，顯示倒地蜈蚣屬的受精前障礙並不明顯。 夏蓳‘Clown Blue’、‘Clown Rose’及母丁香進行自交及互交，於授粉5及6天時，夏蓳自交果莢長度大於與母丁香雜交者，且雜交果莢長度亦不再增長。母丁香自交果莢長度於授粉8天時顯著大於與夏蓳雜交者，雜交果莢長度於授粉4至6天時不再顯著增長。夏蓳與母丁香的種間雜交果莢長度較小，顯示子房內組織及胚珠發育較少。 以夏蓳小丑品種進行自交及種間雜交並採收果莢、收集種子。除了以夏蓳‘Clown Rose’及‘Clown Blue’為種子親與母丁香雜交之兩授粉組合外，其餘以夏蓳小丑品種為種子親與母丁香、倒地蜈蚣或毛葉蝴蝶草雜交之授粉組合，其雜交處理至果莢採收所需時間皆與自交者沒有顯著差異。以夏蓳‘Clown Burgundy’及‘Clown Violet’為種子親與母丁香雜交時，雜交果莢內分別可得到平均4及8粒種子，而其餘以夏蓳小丑品種為種子親與母丁香、倒地蜈蚣或毛葉蝴蝶草雜交之授粉組合皆未獲得種子。多數雜交組合未獲得種子，顯示倒地蜈蚣屬有種間雜交障礙，且可能為受精後障礙。 於授粉後4、8及16天時，分別取下未授粉、自交之夏蓳‘Clown Violet’果莢，另取夏蓳‘Clown Violet’分別與倒地蜈蚣及毛葉蝴蝶草雜交之果莢進行埋蠟切片觀察。授粉4天後，未授粉者之胎座長度較短，而自交者胎座增長較多。未授粉者胚珠甚小，自交者及與倒地蜈蚣雜交者子房各部分胚珠皆有發育，但以自交者之有發育胚珠較多，與毛葉蝴蝶草雜交者僅子房上端胚珠有發育。授粉8天後，未授粉者子房內無明顯發育，其他三授粉處理之胎座及胚珠皆有明顯發育，又以自交者發育較多。與毛葉蝴蝶草雜交者之有發育胚珠集中子房上端，而胎座發育亦集中上端。授粉16天後，未授粉者之子房內仍無明顯變化，自交者之胚珠呈實心狀，可觀察到明顯的胚構造，與倒地蜈蚣雜交者之胚珠萎縮且內部空洞，而與毛葉蝴蝶草雜交者之胚珠亦呈實心狀，且可觀察到胚構造，但胚體小於自交者。 夏蓳‘Clown Violet’自交者之胚乳發育較雜交授粉者多，於授粉8天後，胚乳已充滿胚囊，而與倒地蜈蚣雜交者之胚乳已開始降解，與毛葉蝴蝶草雜交者之胚乳發育較慢。授粉16天時，夏蓳‘Clown Violet’自交者有胚乳包裹的成熟胚，而與倒地蜈蚣雜交者之胚乳已退化，僅有一球胚，而與毛葉蝴蝶草雜交者則有發育較不完整之胚乳及發育至魚雷期或子葉期之胚。 以夏蓳小丑品種為種子親與黃花夏蓳‘Suzie Wong’雜交，以夏蓳‘Clown Rose’為種子親者之結種子數量較多。以夏蓳‘Clown White Blush’、‘Clown Violet’、‘Clown Plum’、‘Clown Blue & White’及‘Clown Rose’為種子親，分別得到少量種間雜交後代。雜交後代株形為半蔓性，花序形態為總狀花序，花冠管狀部分顏色以紫藍色為主，花冠面以黃色底色與紫紅色斑紋為主，花冠面斑紋以種子親之表現為主。

Wishbone flower (Torenia fournieri Linden) is one of the most important annual bedding plants in Taiwan during spring to summer. Four Taiwan-native Torenia species could be used for breeding, to meet the potential demands. However, information of possible hybridization barriers of Torenia is presently limited. This thesis studied self- and interspecific pollination between T. fournieri, T. flava Buch.-Ham. ex Benth., T. concolor Lindl., and T. benthamiana Hance. We observed 1) pollen tube growth within interspecific pistil, 2) growth of hybrid endosperm and embryo, and 3) growth of capsules after self- or interspecific pollination, to clarify hybridization barriers in Torenia. Interspecific progenies between T. fournieri and T. baillonii Godefr. were obtained, and their floral traits were investigated. Under greenhouse conditions, pollen tubes of T. flava and T. fournieri ‘Clown Blue’ in styles of T. flava could be observed at 4 h after pollination by means of fluorescence, while no pollen tubes of T. fournieri ‘Clown Rose’ was found. Pollen tubes of T. concolor and T. benthamiana could be observed in style of T. fournieri ‘Clown White Blush’ and ‘Clown Blue’ at 4 h after pollination, but less clear for T. benthamiana. Capsule lengths of T. fournieri ‘Clown Blue’, ‘Clown Rose’, and T. flava were measured after self- or interspecific pollination. In interspecific pollinations, capsule length did not increase at 5, 6, and 4-6 days after pollination in T. fournieri ‘Clown Blue’, ‘Clown Rose’, and T. flava, respectively. In contrast, capsule length increased after self-pollination in T. fournieri ‘Clown Blue’, ‘Clown Rose’, and T. flava for 5, 10, and 9 days, respectively, and were longer than interspecific pollinated capsules. Capsules and seeds were harvested from T. fournieri ‘Clown’ cultivars after self- or interspecific pollination with T. flava, T. concolor, and T. benthamiana. Except when T. fournieri ‘Clown Rose’ and ‘Clown Blue’ were used as female parents, time to capsule harvest did not differ between tested interspecific pollination and self-pollination combinations. No seed was collected in most of the tested interspecific combinations, but 4 and 8 seeds per capsule were harvested when T. fournieri ‘Clown Burgundy’ and ‘Clown Violet’ were used as female parents, respectively. Unpollinated and self-pollinated T. fournieri ‘Clown Violet’ capsules, and those cross-pollinated with T. concolor and T. benthamiana were collected at 4, 8, and 16 days after pollination (DAP) and sectioned. At 4 DAP, self-pollinated capsules had longer placenta than unpollinated ones. Ovules in unpollinated capsules were small, whereas larger ovules and more ovular growth were identified in self-pollinated and cross-pollinated capsules. Developing ovules were only located in the upper halves in capsules of T. fournieri ‘Clown Violet’ pollinated with T. benthamiana. At 8 DAP, no significant changes were observed in unpollinated capsules, but significant placental and ovular growth were identified in self- and cross-pollinated capsules. At 16 DAP, no changes were observed in unpollinated capsules, whereas embryos could be clearly observed in self-pollinated capsules and those cross-pollinated with T. benthamiana. Meanwhile, empty ovules were observed in capsules pollinated with T. concolor. Ovules had more endosperm development in self-pollinated capsules than cross-pollinated ones. At 8 DAP, embryo sac fully occupied by endosperm were observed in self-pollinated T. fournieri. Degenerating endosperm were observed in T. fournieri cross-pollinated with T. concolor, whereas endosperm developed slower after cross-pollinated with T. benthamiana. At 16 DAP, well-developed embryo and endosperm were observed in self-pollinated T. fournieri. Degenerated endosperm and globular embryos were observed in T. fournieri cross-pollinated with T. concolor, Contrastly, embryos at torpedo or cotyledonal stages with a less developed endosperm were observed in T. fournieri cross-pollinated with T. benthamiana. T. fournieri ‘Clown’ cultivars were used to pollinate with T. baillonii. More seeds were collected when T. fournieri ‘Clown Rose’ was used as female parent. Only few progenies were obtained when T. fournieri ‘Clown White Blush’, ‘Clown Violet’, ‘Clown Plum’, ‘Clown Blue & White’, and ‘Clown Rose’ were used as female parent. The hybrid progenies were semi-prostrate and had racemes. Corolla tube color were mainly violet, and corolla color were mainly yellow combined with red-purple patterns. Colored pattern on corolla were mainly similar to those of seed parents.