鼠尾草屬(Salvia L.)約有900多種物種,含括一、二或多年生草本或灌木,約有140個栽培種,但僅有少數鼠尾草有商業生產或應用於景觀,可藉由種間雜交育成鼠尾草新品種。本研究以紅花鼠尾草(S. coccinea Juss. ex Murr.)、本屬少見黃花且為臺灣特有之黃花鼠尾草[S. nipponica Miq. var. formosana (Hayata) Kudo]、長蕊鼠尾草(S. patens Cav.)及一串紅(S. splendens Sell. ex Roem. & Schult)為材料,觀察花器構造、傳粉機制與花粉離體萌發。進行自交及雜交,觀察花粉管生長、小堅果及其內部發育,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。 紅花鼠尾草‘Snow Nymph’花朵之可育藥室距柱頭近,雄蕊無槓桿運動功能。黃花鼠尾草為典型槓桿狀雄蕊,可育藥室位於上唇瓣內,不育之藥隔下臂阻擋傳粉者取食花蜜。一串紅‘Vista Red’具可育藥室距柱頭近及遠之花朵,雄蕊無槓桿運動功能。紅花鼠尾草‘Snow Nymph’及一串紅‘Vista Red’於無傳粉者環境下可自花結實,而黃花鼠尾草則須傳粉者幫忙傳粉,此三種鼠尾草均無自交不親合性。 於含0.1%酪蛋白水解物之修改過Brewbaker和Kwack培養基中,添加蔗糖及聚乙二醇-3350 (polyethylene glycol-3350, PEG)可改善本屬植物花粉萌發及花粉管生長情形。紅花鼠尾草‘Snow Nymph’花粉適合添加5%-10%蔗糖+30% PEG;黃花鼠尾草花粉適合添加10%蔗糖+20% PEG;而一串紅‘Vista Red’花粉適合添加0%蔗糖+30% PEG或10%蔗糖+20% PEG,‘Vista White’花粉適合添加0%-15%蔗糖+30% PEG或10%蔗糖+20% PEG。本屬植物花粉適合之培養基滲透潛勢為-2.45 MPa至 -1.42 MPa。蔗糖有利花粉萌發但並非萌發之必要成分。 以含10%蔗糖+20% PEG之培養基培養花粉,紅花鼠尾草‘Snow Nymph’及一串紅‘Vista White’於開花後1天之花粉有最佳萌發率,黃花鼠尾草於開花當天有最佳萌發率,而一串紅‘Vista Red’於開花後1天至開花後2天有最佳萌發率。紅花鼠尾草‘Snow Nymph’、黃花鼠尾草及一串紅‘Vista Red’於花朵開放當天柱頭即可接受花粉,無雄蕊先熟現象。 觀察本屬種間雜交花粉管生長情形,以紅花鼠尾草‘Snow Nymph’、黃花鼠尾草或一串紅‘Vista Red’為種子親(♀),與紅花鼠尾草‘Snow Nymph’ (♂)、黃花鼠尾草(♂)、長蕊鼠尾草‘Blue Angel’及一串紅‘Vista Red’ (♂)雜交,除紅花鼠尾草‘Snow Nymph’之花粉管無法穿入黃花鼠尾草之柱頭,及長蕊鼠尾草‘Blue Angel’之花粉管於授粉後2天才見於黃花鼠尾草之花柱末端外,其餘組合皆可於授粉後1天在花柱末端觀察到有花粉管螢光。種間雜交組合中,僅紅花鼠尾草‘Coral Nymph’ (♀)或‘Snow Nymph’ (♀)與一串紅‘Vista Red’ (♂)或‘Vista White’ (♂)雜交可得成熟種子;以黃花鼠尾草(♀)與長蕊鼠尾草‘Blue Angel’ (♂)或與一串紅‘Vista Red’ (♂)雜交之小堅果未膨大;多數雜交小堅果均僅部分膨大,本屬種間雜交多有受精後障礙。 黃花鼠尾草之雌配子體受特化珠被細胞包圍,其自交後胚及胚乳發育較雌配子體無特化珠被細胞包圍之一串紅及紅花鼠尾草慢。若種間雜交胚及胚乳敗育,則小堅果於授粉後8-16天基部褐化及/或皺縮。雜交組合中僅有以紅花鼠尾草‘Coral Nymph’或‘Snow Nymph’為種子親(♀),與一串紅‘Vista Red’ (♂)雜交可得近成熟雜交胚,與黃花鼠尾草(♂)雜交之雜交胚可發育達球胚至心臟胚早期。以一串紅‘Vista Red’為種子親(♀),與紅花鼠尾草‘Coral Nymph’ (♂)或‘Snow Nymph’ (♂)雜交僅得發育達魚雷期之雜交胚,與黃花鼠尾草(♂)雜交者,於授粉後4天胚及胚乳已敗育。 紅花鼠尾草(♀)與一串紅(♂)雜交之小苗具生長弱勢現象,本研究中僅有紅花鼠尾草‘Snow Nymph’ × 一串紅‘Vista Red’及紅花鼠尾草‘Snow Nymph’ × 一串紅‘Vista White’生長至開花階段。二種間雜交組合後代具新植株外觀及花序形態,花朵性狀多介於兩親本之間,且每輪小花數較一串紅多。雜交後代之萼片帶有灰橘、紅或紫色,花冠為橘紅色,此外,紅花鼠尾草‘Snow Nymph’ × 一串紅‘Vista White’之花瓣具白色斑塊。雜交組合後代之花粉具多形性且稔性低,經自交或與親本回交均無法結實。
Salvia L. is a large genus comprised of 900 species of annual, biennial, or perennial herbs, or shrubs. Although about 140 species are in cultivation, only a few salvias are commonly found in commerce and gardens. Interspecific hybridization could contribute more Salvia cultivars. Salvia coccinea Juss. ex Murr., yellow-flowered Taiwan-endemic S. nipponica Miq. var. formosana (Hayata) Kudo, S. patens Cav., and S. splendens Sell. ex Roem. & Schult were collected and studied. The objectives of the study were to determine the floral structure, pollination system, in vitro pollen germination, and hybridization crossability. Pollen tube and nutlet growth were observed after self- or interspecific pollination. Interspecific hybrids of S. coccinea × S. splendens were obtained, and progeny traits were investigated. Observation revealed that S. coccinea ‘Snow Nymph’ had homostylic flowers and immovable stamens. Salvia nipponica var. formosana had typical lever-like stamens, with fertile theca concealed in the upper lip and the sterile lower connective arm restricted access to nectar. Salvia splendens ‘Vista Red’ had pin and homostylic flowers and immovable stamens. Salvia coccinea ‘Snow Nymph’ and S. splendens ‘Vista Red’ could set seeds without pollinators, while S. nipponica var. formosana must require pollinators for pollination. All these three salvias were self-compatible. Supplement of sucrose and polyethylene glycol-3350 (PEG) in the modified Brewbaker and Kwack medium with 0.1% casein hydrolysate could improve pollen germination and tube growth of Salvia. Highest pollen germination was recorded in medium containing 5%-10% sucrose + 30% PEG for S. coccinea ‘Snow Nymph’, 10% sucrose + 20% PEG for S. nipponica var. formosana, 0% or 10% sucrose + 20% PEG for S. splendens ‘Vista Red’. However, pollen of ‘Vista White’ germinated well with media containing 0%-15% sucrose + 30% PEG or 10% sucrose + 20% PEG. The optimum osmotic potential for pollen germination ranged from -2.45 to -1.42 MPa. In these three salvias investigated, sucrose benefited but was not necessary for pollen germination. Effect of flower age on pollen germination rate was measured with medium containing 10% sucrose + 20% PEG. In both S. coccinea ‘Snow Nymph’ and S. splendens ‘Vista White’, pollen had the highest germination rate at 1 day after anthesis. In S. nipponica var. formosana, pollen had the highest germination rate at anthesis. Highest germination rate of S. splendens ‘Vista Red’ was obtained at 1 and 2 d after anthesis. Stigma had became receptive at anthesis in S. coccinea ‘Snow Nymph’, S. nipponica var. formosana, and S. splendens ‘Vista Red’, indicating these plants were not protandrous. Among all cross combination tested in this study, pollen tubes were observed in the style base at 1 d after pollination when S. coccinea ‘Snow Nymph’, S. nipponica var. formosana, or S. splendens ‘Vista Red’ were crossed with S. coccinea ‘Snow Nymph’, S. nipponica var. formosana, S. patens ‘Blue Angel’, or S. splendens ‘Vista Red, respectively. Pollen tubes of S. coccinea ‘Snow Nymph’ were arrested on stigma of S. nipponica var. formosana. Pollen tubes of S. patens ‘Blue Angel’ were not observed in style base of S. nipponica var. formosana until 2 d after pollination. Mature seeds were obtained only when S. coccinea ‘Coral Nymph’ or ‘Snow Nymph’ as female parents crossed with S. splendens ‘Vista Red’ or ‘Vista White’. Nutlets did not enlarge when S. nipponica var. formosana was crossed with S. patens ‘Blue Angel’ or S. splendens ‘Vista Red’. In most cross combinations, hybrid nutlets showed only partial development indicating that post-fertilization barriers existed. The megagametophyte of S. nipponica var. formosana was, but those of S. splendens and S. coccinea were not, surrounded by a differentiated integumental cell layer. Selfed-embryo and endosperm of S. nipponica var. formosana developed slower than S. splendens and S. coccinea. Most hybrid embryo and endosperm aborted and resulted in basal shrinking and/or browning nutlet at 8-16 d after pollination. Nearly-mature embryo was obtained in S. coccinea ‘Coral Nymph’ or ‘Snow Nymph’ as female parent crossed with S. splendens ‘Vista Red’. Embryo reached globular to early-heart stage in S. coccinea ‘Coral Nymph’ or ‘Snow Nymph’ as female parent crossed with S. nipponica var. formosana. Embryo most reached torpedo stage in S. splendens ‘Vista Red’ crossed with S. coccinea ‘Coral Nymph’ or ‘Snow Nymph’. In contrast, embryo and endosperm aborted 4 d after pollination when S. splendens ‘Vista Red’ crossed with S. nipponica var. formosana. Hybrid weakness was observed in S. coccinea × S. splendens progenies. In this study, only progenies of S. coccinea ‘Snow Nymph’ × S. splendens ‘Vista Red’ and S. coccinea ‘Snow Nymph’ × S. splendens ‘Vista White’ grew and flowered. Both hybrid progenies had new plant and inflorescence appearance. Most flower characteristic traits of both hybrid progenies were between two parents. The selected progenies had more nodal florets than S. splendens. Both hybrid progenies had green with gray-orange, red or purple calyx and orange-red corolla. Corolla had white blotch in progenies of S. coccinea ‘Snow Nymph’ × S. splendens ‘Vista White’. Both hybrid progenies had pollen polymorphism with low fertility and could not set seed after self-pollination or backcross with both parents.
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