Possible pathways of the gene flow inTaraxacum sect.Ruderalia

Reproductive behaviour and the pathways of gene flow among ploidy levels were studied experimentally inTaraxacum sect.Ruderalia. Diploid, triploid and tetraploid individuals were sampled from mixed diploid — polyploid natural populations. 136 experimental hybridizations between the plants of different ploidy levels were performed. Seeds resulting from these crosses, those obtained from isolated anthodia as well as from open pollinated anthodia (both from cultivated and wild plants) were subjected to the flow-cytometric seed screening (FCSS) to determine ploidy levels in the progeny and to infer breeding behaviour of maternal plants. Three possible pathways of the gene flow were studied: (A) fertilization of sexuals by pollen of apomicts, (B) B_III hybrid formation, (C) facultative apomixis. Diploid maternal plants when experimentally crossed with triploid pollen donors produced diploids and polyploid progeny, while when pollinated with a mixture of the pollen of diploids and triploids or insect pollinated, no polyploids were discovered. It seems that in the mixture with the pollen of diploids, the pollen of triploids is ineffective. Tetraploids produce hybrids much easier with diploid mothers and their role in wild populations requires further study. Triploid mothers, even those with subregular pollen did not show traces of facultative apomixis. B_III hybrids were present in the progeny of both triploids and tetraploids, in tetraploids in quite high percentages (up to 50% of the progeny in some crosses).