Role of breeding modes, ploidy levels and environmental factors on the structure of an apomictic complex

We analyzed breeding modes in most species and cytotypes of subgenus Pilosella in the field. It turned out that the relationship between breeding modes and ploidy levels is much less clear than indicated in the literature. For example, we found populations with sexual pentaploids as well as sexual aneuploids. Surprisingly, apomicts are often seed parents of many hybridogenous types occurring in the field (Krahulec et al. 2004b, Fehrer et al. 2005). This is related to a higher proportion of addition hybrids in their progeny (unpublished data).

The analysis of progeny from hybridization experiments as well as from open pollinated mother plants in the field showed a high degree of variation with respect to ploidy levels. Some ploidy levels, such as octoploid and polyhaploid (and also aneuploid) are regularly present in artificial crosses, but absent or very rare in the field. We are trying to identify stages in their life cycle in which the polyhaploids and/or some of the hybrid cytotypes are eliminated by comparing ploidy of seeds and seedlings (Krahulec et al. 2006). The results suggest a higher mortality during germination and early establishment phase in those progenies, which have arisen from reduced egg cells (polyhaploids and hybrids). Conversely, apomictically derived progenies and hybrids which originated from unreduced egg cells displayed a higher survival rate. We germinated seeds under environmental conditions and did implant experiments when we compared different plants. It seems that the stage of germination is an important evolutionary filter. For that reason we compared the population structure of some habitats with high establishment rate. We found a high diversity of different cytotypes in these experiments like, for example, a high proportion of aneuploids.

We found that even on the fine scale different hybridogenous types of subgenus Pilosella have strong preferences with respect to environmental parameters like community structure. Such types with different ecological demands were tested by implanting them back to the field and following their growth with respect to composition and biomass of the respective plant communities (KrbcovŠ 2001).

Research

Breeding modes, ploidy and ecology