The results indicate that hybridization rather than polyploidization seems to be the functional activator of apomictic reproduction in the synthetic Ranunculus hybrids. Other than in the F 1 generation, diploid Ranunculus F 2 hybrids formed B III seeds and fully apomictic seeds. The frequency of apospory was found to depend on dosage effects since a significant increase in apospory was observed, when both F 1 parents, rather than just one, were aposporous. Microscopic analysis of the female gametophyte formation indicated spontaneous occurrence of aposporous initial cells and several developmental irregularities.
Complete manifestation of apomixis was determined by measuring single mature seeds by flow cytometric seed screen. auricomus species was analyzed for aposporous initial cell formation by DIC microscopy. In this study, the second generation of synthetically produced homoploid (2 x) and heteroploid (3 x) hybrids derived from sexual R. The Ranunculus auricomus complex comprises diploid sexual and polyploid apomictic species and represents an excellent model system to gain knowledge on origin and evolution of apomixis in natural plant populations. Furthermore, most natural apomicts were found to be polyploids and/or hybrids. Apomixis, the asexual reproduction via seed formation, comprises several essential alterations in development compared to the sexual pathway. Hybridization and polyploidization play important roles in plant evolution but it is still not fully clarified how these evolutionary forces contribute to the establishment of apomicts. Department of Systematics, Biodiversity and Evolution of Plants, Albrecht-von-Haller Institute for Plant Sciences, University of Göttingen, Göttingen, Germany.
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