Co-Innovation Center for Sustainable Forestry in Southern China, Nanjing Forestry University and International Cultivar Registration Center for Osmanthus, Nanjing, Jiangsu, P. R. China.
Department of Plant Science, College of Biology and the Environment, Nanjing Forestry University, Nanjing, Jiangsu, P. R. China.
PLoS One. 2019 Sep 5;14(9):e0221898. doi: 10.1371/journal.pone.0221898. eCollection 2019.
Androdioecy is one of the rarest sexual systems among plants, characterized by males co-occurring with hermaphrodites. Osmanthus delavayi (Oleaceae), an ornamental shrub from southern China, is known to have both male and hermaphrodite individuals, but little is known regarding the breeding system of this species and whether it is functionally androdioecious, and how this potentially evolved. In this study, we explore the characteristics of the breeding system of O. delavayi through the study of phenology, sex ratio, floral organ morphology, pollen number, stigma receptivity, artificial pollination, pollinators, and gene flow within and between populations, while also discussing the evolution and maintenance of androdioecy within the genus. The proportion of males was less than 0.5 and the out-crossing index (OCI) was 5. Morphological androdioecy was observed, with hermaphrodite flowers having fertile pistils, while male flowers had degenerated pistils. Males and hermaphrodites both had large amounts of small and fertile pollen grains, although the pollen number of males was ca. 1.21 × more than that of hermaphrodites, and pollen was generally smaller. Self-pollination was found to produce a much lower fruit set than outcrossing under natural conditions. Gene flow between males and hermaphrodites within a population was greater (1.007) than that between populations (0.753). All these results indicate that O. delavayi is functionally androdioecious, which may be an intermediate state in the evolutionary transition from hermaphroditism to dioecy.
雌雄同体是植物中最罕见的性系统之一，其特征是雄性与雌雄同体共存。中国南方的观赏灌木桂花（木樨科）已知既有雄性个体又有雌雄同体个体，但对该物种的繁殖系统知之甚少，也不知道它是否在功能上是雌雄同体，以及这种情况是如何进化的。在这项研究中，我们通过研究物候学、性别比例、花器官形态、花粉数量、柱头可授性、人工授粉、传粉者以及种群内和种群间的基因流，来探讨桂花的繁殖系统特征，同时还讨论了雌雄同体在属内的进化和维持。雄性的比例小于 0.5，异交指数（OCI）为 5。观察到形态雌雄同体，雌雄同体花具有可育的雌蕊，而雄花花则有退化的雌蕊。雌雄花都有大量小而可育的花粉粒，尽管雄花花粉数量约为雌雄同体花的 1.21 倍，但花粉通常较小。在自然条件下，自花授粉产生的果实比异交授粉产生的果实要少得多。同一种群内雄性和雌雄同体之间的基因流（1.007）大于种群之间的基因流（0.753）。所有这些结果表明，桂花在功能上是雌雄同体的，这可能是从雌雄同体到雌雄异株进化过渡的中间状态。
