倒地蜈蚣屬植物之花粉發芽與種間雜交

Abstract

夏蓳(Torenia fournieri Linden)是世界重要花壇植物，臺灣具有同屬原生種原，可選育本土之自有品種。本研究以夏蓳商業品種、具匍匐性且為臺灣原生之毛葉蝴蝶草(T. benthamiana Hance)、黃花夏蓳(T. baillonii Godefr.)與四倍體雜交夏蓳(T. fournieri × T. benthamiana) Cb5-M612為材料，觀察花器構造、傳粉與授粉模式與花粉離體發芽。進行自交及雜交，觀察花粉管生長、果莢、胚珠、胚與胚乳發育，以瞭解本屬物種間之雜交能力。另調查種間雜交後代之性狀，供後續種間雜交選育參考。 選自夏蓳‘Clown Rose’與毛葉蝴蝶草胚珠培養並多倍體化之四倍體雜交夏蓳Cb5-M612與黃花夏蓳，花朵之長雄蕊基部皆具有花絲附加物，而花藥囊黏聚，在花絲延伸將花藥囊往花冠外推後，有利昆蟲推動附加物產生槓桿運動而傳粉。四倍體雜交夏蓳Cb5-M612長雄蕊於開花後第1及第2天呈槓桿運動位置，黃花夏蓳長雄蕊則於花開當天即呈槓桿運動位置並持續到開花後第2天，隨後因花藥囊分開而失去槓桿運動能力。 四倍體雜交夏蓳Cb5-M612與毛葉蝴蝶草於開花當天之花粉發芽率最高，隨開花天數增加而下降，黃花夏蓳於開花前一天花粉發芽率最低，隨開花天數增加而增加。四倍體雜交夏蓳Cb5-M612長、短雄蕊之花粉發芽率皆以開花當日最高；黃花夏蓳長雄蕊花粉發芽率於開花前1天最低，短雄蕊在開花前1天至開花後第1天之花粉發芽率無顯著差異，兩花粉發芽率皆隨開花天數增加而增加。 以四倍體雜交夏蓳Cb5-M612為種子親與夏蓳‘Kauai Rose’雜交授粉後8小時可觀察到花粉於柱頭上發芽，亦可於花柱末端觀察到花粉管螢光，但以夏蓳‘Kauai Rose’為種子親與四倍體雜交夏蓳Cb5-M612雜交授粉後8小時，無法於柱頭與花柱末端觀察到花粉管螢光。取黃花夏蓳為種子親與毛葉蝴蝶草雜交授粉後8小時也可觀察到花粉於柱頭上發芽，亦可於花柱末端觀察到花粉管螢光，但皆未能順利穫得種子。 黃花夏蓳自花授粉，胚與胚乳發育完整。於開花前2天除雄再同株異花自交之胚與胚乳可發育，但較自花授粉者發育緩慢，授粉後第16天，胚發育至球型胚，但胚乳有退化、降解。以黃花夏蓳為種子親與毛葉蝴蝶草雜交授粉後4天果莢些微膨大，胚與胚乳持續發育；授粉後第8天，胚珠內部發育充實，胚發育近球胚期，胚乳持續發育；授粉後第12天，胚珠充實，胚發育達球胚期；授粉後第16天，胚珠呈乾癟萎縮，胚已敗育退化，且胚乳降解。 以夏蓳‘Kauai’系列、‘Duchess Rose’、‘Panda Rose’為種子親與毛葉蝴蝶草進行雜交，雜交授粉後第18天取胚珠置於含3 g·L-1蔗糖、7 g·L-1洋菜及8 g·L-1花寶1號之培養基，各雜交組合之發芽率介於70% - 90%。 夏蓳‘Kauai’系列、‘Duchess Rose’與毛葉蝴蝶草雜交所得後代株型皆為半匍匐，各組合花色介於淡紫色至紫羅蘭色之間，唇瓣近喉部皆有黃色斑點。夏蓳‘Kauai Rose’與毛葉蝴蝶草之雜交後代節間長度及平均花序長度顯著短於以‘Clown Rose’及‘Duchess Rose’為種子親者。 根據株型、分枝性、花朵數及花朵顏色，從七個雜交胚培養組合中各選出一個單株，皆能於日/夜溫15/13℃下生長。依據公告之倒地蜈蚣屬品種檢定方法進行新品種性狀檢定。

Wishbone flower (Torenia fournieri Linden) is an important summer bedding worldwide. Taiwan-native and trailing Torenia benthamiana Hance could be used for breeding. Commercial T. fournieri cultivars, T. benthamiana, yellow wishbone flower (T. baillonii Godefr.), and tetraploid torenia hybrid (T. fournieri × T. benthamiana) Cb5-M612.were included in this study. The objectives were to 1) observe floral organ arrangements in relation to pollen transmission and pollination, 2) measure in vitro pollen germination, 3) observe pollen tube, capsule, ovule, embryo, and endosperm after self- and cross-pollination, 4) document progeny phenotypes from crossing various T. fournieri cultivars with T. benthamiana. In Cb5-M612 and T. baillonii, the base of longer-paired stamen had appendages, and the pollen sacs are fused. The filament extension, caused pollen sacs outward, resulting in lever action by insect forage to transmit pollen. Longer-paired stamen of Cb5-M612 positioned to lever action at 1 and 2 days after anthesis, whereas T. baillonii positioned from anthesis to 2 days after anthesis, and subsequently lost lever action due to the separation pollen sacs. Stigma of both species was bilabiate when longer-paired stamen reached the lever action position. Cb5-M612 and T. benthamiana had higher pollen germination percentage at anthesis, and decreased thereafter, while T. baillonii had lower pollen germination at 1 day before anthesis, and increased afterwords. Pollen from longer- and shorter-paired stamen in Cb5-M612 had higher germination percentage at anthesis. In T. baillonii, pollen from longer-paired stamen had the lowest germination percentage at 1 day before anthesis. The germination of pollen from shorter-paired stamen did not differ 1 day before or after anthesis. Pollen germination on stigma and pollen tube growth to the end of style was observed at 8 hours after pollinating Cb5-M612 with T. fournieri ‘Kauai Rose’, but no sign of pollen germination or pollen tube growth was seen in the reciprocal cross. Pollen germination and pollen tube growth could be observed at eight hours after pollinating T. baillonii with T. benthamiana, but no seed was obtained subsequently. Anatomical observation revealed that embryo and endosperm developed well after self-pollinating T. baillonii without emasculation. Contrastly, after emasculation, those self-pollinated at two days before anthesis resulted in retarded embryo, and degenerating endosperm at 16 days after pollination, when embryo only reached globular stage. For T. benthamiana × T. baillonii with, capsule enlarged only slightly at 4 days after pollination, embryo reached globular stage and endosperm continued to develop at 8-12 days after pollination, and ovule was shriveled and both embryo and endosperm were degenerating at 16 days after pollination. Torenia fournieri ‘Kauai’ series, ‘Duchess Rose’, and ‘Panda Rose’ were pollinated with T. benthamiana. Their hybrid ovules were then cultured on medium containing 3 g·L-1 sucrose, 7 g·L-1 agar, and 8 g·L-1 Hyponex No.1 at 18 days after pollination. Germination of the hybrid ovules ranged from 70% to 90%. The F1 hybrid progenies between T. fournieri and T. benthamiana were all trailing, and the flower color ranged lavender to violet, with yellow spot near throat on labiate corolla lobe. Internode and inflorescence lengths of the progenies were shorter when ‘Kauai Rose’ was used as female parent, as compared to ‘Clown Rose’ and ‘Duchess Rose’.