濒危植物凹叶厚朴的花部综合特征和繁育系统

为了解凹叶厚朴(Magnolia officinalis subsp.biloba)濒危的生殖生物学原因,通过野外观测,运用杂交指数、花粉-胚珠比、花粉活力和柱头可授性观测、人工授粉和套袋实验等方法,对凹叶厚朴种群的开花生物学、繁育系统进行了研究。结果表明:凹叶厚朴单花花期一般为4～5d,单花花期根据形态和散粉时间可分为4个时期:蕾期、初开期、盛开期和凋零期;种群于4—5月开花,一般开花历时30d左右,但不同地点、年份间有所差异;种群无开花高峰,单株平均开花数量为171.4～188.8朵,平均开花振幅为5～6朵·株-1·d-1;凹叶厚朴杂交指数为4,花粉胚珠比为5728.86,结合人工套袋和授粉实验结果可确定,繁育系统为异交,传粉过程需要传粉者;花粉活力较高(94%),且花粉活力可维持至散粉后的第6天。散粉后,柱头可授性显著下降,花粉高活力期与柱头可授期有5～6h的重叠;自然状况下结果率和单果出种百分率低,异株异花授粉可明显提高结果率和单果出种百分率,二者相对自然状况分别提高14.25%和43.66%。表明自然状态下传粉效率低、柱头最佳可授期短、同株自花授粉败育严重是其濒危的主要生殖生物学原因。

Floral syndrome and breeding system of endangered species Magnolia officinalis subsp biloba

Magnolia officinalis subsp. biloba is an endangered species in China. To understand the reproductive biological causes of the endangering, a field observation was conducted to study the flowering biology and breeding system of three M. officinalis subsp. biloba populations in Zhejiang Province, with the focus on the outcrossing index, pollen-ovule ratio (P/O), pollen vitality, and stigma receptivity under natural condition and artificial pollination and bagging. Generally, the flowering of M. officinalis subsp. biloba lasted 4-5 days, and the flowering process for one flower could be divided into four periods based on the flower’s morphology and pollen dehiscence, i.e., bud swelling, flower opening, full blooming, and flower withering. The population’s flowering started in April and ended in May, with the duration being about 30 days but differed at different sites and in different years. The populations had no flowering peak. The mean flower number per plant was 171.4-188.8, and the mean flowering amplitude was 5-6 per plant per day. The outcrossing index was 4, and the pollen-ovule ratio (P/O) was 5726.86. Under artificial pollination and bagging, the breeding system was of xenogamy, the pollen vitality was 94% and could be maintained for 6 days after pollen dehiscence, the stigma receptivity decreased significantly after pollen dehiscence, and there was only a 5-6 hour overlap between high stigma receptivity and pollen dehiscence. Under natural condition, the fruit setting rate and the seed setting rate per fruit were low, but outcrossing increased the two rates by 14.25% and 43.66%, respectively, as compared with the control. It was concluded that the low pollination efficiency, short duration of stigma’s optimal receptivity, and sterility induced by self-pollination were the main reproductive biological causes of the endangering of M. officinalis subsp. biloba.