峨眉拟单性木兰的开花生物学特性与繁育系统

Flowering biological characteristics and breeding system of Parakmeria omeiensis

关键词:  峨眉拟单性木兰, 极小种群, 开花生物学, 繁育系统, 木兰科

Key words:  Parakmeria omeiensis, extremely small populations, flowering biology, breeding system, Magnoliaceae

摘要:

为阐明峨眉拟单性木兰(Parakmeria omeiensis)在自然条件结实率低的原因和确定最佳人工授粉时期,该文通过观察峨眉拟单性木兰的开花动态,采用杂交指数估算、花粉胚珠比、花粉活力及柱头活性检测、人工授粉试验等方法对其繁育系统进行了研究。结果表明:(1)植物园保育的峨眉拟单性木兰花期在4月底到5月中下旬,持续17～23 d,雄株始花期比雌株早3～4 d,但两者花期可遇。(2)两性花经检测雄蕊败育,实为功能上的雌性,部分雄株个体的雄花上残留1～2个心皮,其性别分化是通过雌、雄蕊选择性败育形成的,为隐性雌雄异株(cryptic dioecy)。(3)雄花、两性花开放经历佛焰苞开裂、花被片开裂、展开、闭合、二次开放、凋落6个阶段,历时4 d。(4)雄花初次展开时花粉活力最高,达92.8%,开花2 d后活力显著下降; 两性花柱头在花被片展开期可授性最强,盛开后柱头部分可授。(5)杂交指数为5,P/O比为2.14×10⁴。(6)套袋试验表明,峨眉拟单性木兰不能进行自花传粉,人工异花授粉的结实率和出种数显著高于自然授粉,且不存在无融合生殖。这说明峨眉拟单性木兰繁育系统为专性异交,传粉过程需要传粉媒介,自然条件下结实率低,主要是受传粉昆虫和柱头可授期短的限制。

Abstract:

In order to explain the reasons for the low seed-setting rate of Parakmeria omeiensis in natural condition and determine the optimum pollinating time. The floral character were studied through field observation in Mount Emei, the type of breeding system was estimated by out-crossing index(OCI), the pollen-ovule ratio(P/O), pollen viability and the stigma receptivity, and the artifical pollination experiments were carried out. The results were as follows:(1)The florescence of P. omeiensis was from late April to mid-late May. Male plants bloomed 3-4 d earlier than female plants, and their florescence were overlapped.(2)Bisexual flowers were actually female in reproductive function, 1-2 carpels remained on the male flower of some male plants. The selective abortion of either pistil or stamens led to sex differentiation. So P. omeiensis belongs to cryptic dioecy.(3)The flowering process followed six stages from spathe dehiscence, tepal dehiscence, spreading, closing, the second spreading to flowers withering, which took 4 d.(4)The viability of pollen in male flowers reached the highest(92.8%)during the first spreading, and then descended greatly after 2 d. The stigmas of bisexual flowers were strong receptivity when all tepals were spreading, while some stigmas were receptive after bloo-ming.(5)The out-crossing index(OCI)was five and pollen/ovule was 2.14×10⁴, which indicates that P. omeiensis should be classified as an allogamous plant.(6)The artificial pollination revealed the self-pollination phenomenon did not exist and had no apomixis phenomenon. The fruit-setting rate and seed-setting rate were significantly higher than that of natural pollination. In conclusion, the breeding system of P. omeiensis was obligate cross-pollination which requires pollinators, and its fruit-setting rate was limited by pollinators and the short stigma receptivity under natural conditions.