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. 2022 Jun 21;11(13):1639.
doi: 10.3390/plants11131639.

Variation of Residual Sexuality Rates along Reproductive Development in Apomictic Tetraploids of Paspalum

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Variation of Residual Sexuality Rates along Reproductive Development in Apomictic Tetraploids of Paspalum

Anna Verena Reutemann et al. Plants (Basel). .

Abstract

Most apomictic plants are facultative, maintaining the ability to reproduce sexually at different frequencies depending on the taxa, ploidy, and reproductive stage. In this context, Paspalum species are good model systems for studies evaluating the varying levels of apomixis expression. We aimed to identify, in apomictic tetraploid Paspalum species, the degree of apomixis and residual sexuality in three stages of reproductive development, and if their expression varies along them in order to predict their realized impact on the genetic diversity of future generations. Three main stages in the reproductive development (i.e., ovule, seed, and progeny) were studied in tetraploids from populations of P. cromyorhizon and P. maculosum. Mature ovules were studied using cytoembryological analysis, seeds by flow cytometry, and progeny tests with molecular markers. The expression of sexuality and apomixis was compared in each stage. We observed a decline in expression of sexual reproduction through the consecutive stages, jointly with an increase of apomixis expression. Both species showed at least one tetraploid plant capable of producing progeny by sexual means. These small rates of sexually originated progeny prove the ability of apomictic plants to produce low levels of genetic variation through rare events of sexuality. This study also demonstrates the importance of analyzing different reproductive stages in order to get a whole picture of the reproductive outcomes in plant evolution.

Keywords: P. maculosum; Paspalum cromyorhizon; apospory; cytoembryology; facultative apomixis; flow cytometry; polyploidy; progeny test; residual sexuality.

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Conflict of interest statement

The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.

Figures

Figure 1
Figure 1
Number of genotypes (nG) considering varying numbers of mutational steps (S). (A) Genotype numbers in the progeny of six apomictic genotypes from two populations of P. maculosum. (B) Genotype numbers in the progeny of 11 apomictic genotypes of four populations of P. cromyorhizon. Apomictic genotypes with all clonal progeny considering S = 0 are not presented (C1-20, C2-15, C3-15 and 19, C4-3 and 12). With increasing S, the nG decreased in nearly all the progenies. nG = 1 indicates that all the offspring have the maternal genotype.
Figure 2
Figure 2
Observed proportions of the sexual (A) and apomictic (B) pathway in three reproductive stages: ovules (O), seeds (S), and progeny (P) in P. maculosum and P. cromyorhizon.

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