Fertility and Viability of Pollen Grains of Taraxacum officinale Wigg. s.l. (Asteraceae, Magnoliopsida) in a Gradient of an Anthropogenically Transformed Environment

摘要

The fertility and viability of pollen grains of two morphological forms of Taraxacum officinale Wigg. s.l. were estimated. These forms compose common coenopopulations growing in various coenotic and edaphic conditions. The forms studied possess developed gynoecia-a large number of fertile pollen grains capable of germinating under certain temperature conditions. This fact points to the amphimictic properties of the plants. Comparison of the data on the fraction of fertile pollen grains and seed productivity allows assuming that some seeds develop without fertilization. This can be considered as evidence of the apomictic properties of plants. Therefore, the presence of facultative apomixis in the species considered was confirmed indirectly in our work. The fertility of pollen grains was shown to be a characteristic of the male gametophyte that was more environmentally dependent than its viability. Under favorable conditions, the share of fertile pollen grains in f. dahlstedtii and f. pectinatiforme differ insignificantly. Under stress, the differences between the dandelion forms by this index increase. This can be considered as a mechanism of adaptation to adverse environmental factors. The revealed differentiation of the morphological forms of dandelions by the index of pollen grain fertility suggests that edaphic and coenotic stresses increase the differences between them in the degree of apomictic and amphimictic properties. The morphological forms of dandelions, by realizing two reproductive strategies under stress, ensure both the abundance and the genetic heterogeneity of the coenopopulations. The morphological forms studied do not differ in the proportion of viable pollen grains. This index increases in the gradient of coenotic competition only to a certain extent, which can be considered as a manifestation of the properties of the facultative apomict.