Differential effects of polyploidy and diploidy on fitness of apomictic Boechera.

The co-occurrence of apomixis (asexual reproduction) and polyploidy in plants has been the subject of debate in regard to the origin and evolution of asexuality. In recent years, polyploidy has been postulated as a maintenance and stabilization factor rather than as a source of apomixis origin. It is assumed polyploidy facilitates the compensation for mutation accumulation, and hence, the rare occurrence of diploid apomixis indirectly supports this finding. Nevertheless, diploid apomicts exist and are successful, especially in the genus Boechera. While comparing phenotypic traits, fitness-related traits and apomixis penetrance between both diploid and triploid apomicts in the genus Boechera, it was expected to find trait variance that can be attributed to ploidy. Surprisingly, little trait variation could be assigned to ploidy, but rather trait variations were mainly genotype-specific. Additionally, it is shown that paternal contribution is very important for trait success, even though all offspring are genetically identical to the mother plant. This harbors implications for the introduction of apomixis into crop plants, considering the effects of paternal contribution during asexual reproduction. Nevertheless, polyploidy is an efficient way to buffer deleterious mutations, but the flexibility of diploid apomicts of the genus Boechera for rare sexual events contributes to their success in nature.