Facultative apomixis and development of fruit in a deciduous shrub with medicinal and nutritional uses.

Knowledge of reproductive biology of plants is crucial to understand their natural mode of propagation, which may aid in conservation and crop improvement. The reproductive details are also crucial for beginning the cultivation of a potential crop on a commercial scale. Fruits of sea buckthorn, Hippophae rhamnoides, are used in a variety of medicinal and nutritional products. So far, fruits are collected from the female plants in the wild. It is known that the species fruits profusely and also propagates by forming root suckers, but the details of sexual reproduction are not available. We investigated the mode of reproduction and development of fruits from natural populations of sea buckthorn. Megasporogenesis and megagametogenesis were studied through resin-embedded sectioning and ovule-clearing methods, and fruit development through histochemistry. The study of mitosis and male meiosis showed that the plants at the site were diploid (2n = 2x = 24). The embryo sac may develop either through the monosporic pathway and differentiates into 'Polygonum type' or aposporously into 'Panicum type'. The embryo may develop by sexual and adventitious pathways. Thus, sea buckthorn is a facultative apomict. The occurrence of diverse reproductive pathways assures the possibility of generation of novel genotypes through sexuality, while apomictic reproduction maintains adaptive genotypes and ensures reproduction in the absence of pollination. Anatomical details suggest that the fruit of sea buckthorn may be appropriately described as a pseudo-drupe.