春石斛雜交障礙之探討

春石斛為具商業價值的觀賞植物，其育種因雜交不親和性而面臨雜交障礙。為探討春石斛之雜交授粉後發育情形及雜交障礙類型，本篇研究以Den. Comet King ‘Akatsuki’為主要材料，與其他13種春石斛進行雜交試驗。實驗說明春石斛授粉後雌配子體才開始發育生長，授粉後1週花粉已萌芽，授粉後2週花粉管已進入子房，授粉後3週花粉管隨著子房膨大更加深入，授粉後12週胎座上有數以千計的小突起，授粉後20週已生成眾多具胚種子，授粉後6個月種子成熟。本研究之春石斛雜交障礙可分為授粉後1-2週落花及生成無胚種子兩種，前者為受精前親本間雜交不親和或花粉不正常造成，後者則為雜種胚敗育死亡或未受精。深入探討產生雜交障礙的2種春石斛，Den. Yellow Song ‘Candy’花粉46.0%為正常的四分體，推測雜交障礙為親本間不親和所致；Den. Love Memory ‘Fizz’花粉僅14.8%為正常的四分體，配子體減數分裂不正常，推測其為異源三倍體。關於雜交障礙之克服，本實驗使用切除花柱授粉、注入花柱分泌物及酒精處理等3種方法，其中注入花柱分泌物之效果最佳，花粉管生長速度快，且授粉後12週觀察種子量有增加趨勢。

關鍵字

雜交不親和性；授粉；小孢子群型態；異源三倍體；花柱分泌物

並列摘要

Nobile-type Dendrobium is an attractive ornamental plant of great business value. One crucial barrier, however, underlies its breeding: the cross-incompatibilities among Dendrobium cultivars. To investigate the development of cross-pollinated Dendrobium, as well as to identify the crossing barriers, interspecific crosses between Den. Comet King ‘Akatsuki’ and 13 other Dendrobium cultivars were conducted. The results showed that female gametophyte began to develop after pollination. One week after pollination, the pollen germinated; in the second week, the pollen entered the ovule. In three weeks, the ovule enlarged and the pollen tubes grew deeper. After 12 weeks, thousands of protrusions were observed on surface of the placenta. By the end of the twentieth week, seeds with functional embryos were formed. Six months after pollination, the seeds were fully matured. Based on the observations, crossing barriers can be coded into two major types: flowers dropping 1-2 weeks after pollination and seeds forming without embryo. The former is caused by either cross-incompatibility or abnormal pollen grain; the latter is caused by either embryo abortion or unfertilized ovule. In the current study, two of the 13 target Dendrobium flowers confronted conspicuous crossing barriers: the Den. Yellow Song ‘Candy’ and the Den. Love Memory ‘Fizz.’ Sporad type observations manifested that Den. Yellow Song ‘Candy’ yielded 46.0% of normal tetrads. It was considered that the crossing barrier is a result of cross-incompatibility. As for Den. Love Memory ‘Fizz,’ merely 14.8% of the pollen were found normal tetrads, which is a result of the gametophyte undergoing aberrant meiosis; on reasonable inference is that Den. Love Memory ‘Fizz’ is an allotriploid. In reducing the above-mentioned crossing barriers, three treatments were employed: cut-column pollination, stigmatic exudate injection and ethanol treatment. Among all, stigmatic exudate injection exerted the most significant effect. After the treatment, pollen tubes grewing faster, and the amount of seeds was increased, as was observed by the end of the twelfth week.