CONICET | Buscador de Institutos y Recursos Humanos

The diploid cytotype of Paspalum rufum (Poaceae) reproduces sexually and is self-sterile. However, recurrent autopolyploidization through 2n + n fertilization as well as some capacity for apomixis reproduction has been documented. The objectives of this work were to analyze the variation in the functionality of apomixis components in diploid genotypes and explore the inheritance of apospory in a F segregant 1 populations derived from individuals with contrasting reproductive behavior. Experiments were initiated by selecting five individuals from three natural diploid populations (R2, R5 and R6). The reproductive mode of each plant was determined by flow-cytometric seed screen analysis (FCSS) and clearing of ovaries at anthesis. Previous works determined that all genotypes formed seeds by sexuality in openpollination conditions. However, in con-specific and inter-specific inter-ploidy crosses and self-pollination induction, several genotypes evidenced variations in the reproductive pathways. While all plants from populations R2 and R6 formed seeds exclusively by sexuality, three genotypes from the R5 developed seeds from both meiotic and aposporous embryo sacs, and one of them (R5#49) was able to complete the apomictic pathway (apospory + parthenogenesis + pseudogamy). Interestingly, embryological observations revealed the presence of both meiotic and aposporous embryo sacs in all genotypes analyzed, suggesting that apospory could be uncoupled from parthenogenesis. Individuals with contrasting reproductive behavior were crossed and the resultant F population was analyzed by 1 cytoembryological observations. Genetic analysis of the mode of reproduction of hybrids showed a 15:1 ratio between aposporous vs nonaposporous (meiotic) plants. Furthermore, the percentage of apospory showed a transgressive segregation and five types of phenotypes (according to the % of aposporous sacs) could be identified. The results presented here demonstrate the existence of variation in the functionality of apomixis components in natural diploid genotypes of P. rufum. Moreover, the inheritance analysis suggested the presence of at least two additive genes affecting apospory expression. Individuals with contrasting reproductive behaviors identified here are valuablematerial for additional studies of apomixis components at the diploid level. Moreover, analysis of their expression patterns, quantification of specific transcript levels and understanding of their regulation mechanisms could help to design new strategies for recreating apomixis in diploids. In addition, the different proportions of apospory observed in the F hybrids open the possibility for studying the mechanisms controlling the expressivity of the trait in a diploid genetic background.

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