Gene flow between Taraxacum koksaghyz (TKS) and other dandelions


Three approaches were adopted to test the potential of gene flow between TKS and its congeners. The first step was to find principles and limits of crossability of TKS with various pollen donors belonging to a representative selection of Taraxacum sections from Europe and Asia.

One of the artificial hybrids in the experimental garden, Institute of Botany, Academy of Sciences, Průhonice, Czech Republic

We tested separately the crossability of TKS and sexual dandelions (diploids and tetraploids). Seven sexual species (belonging to five Taraxacum sections) were used as pollen donors and a moderate crossability was observed (with mean number of hybrid achenes varying between 15 and 20 % in the backcrosses). Hybrids are diploid and sexual, quite viable, occasional sterile triploids are found in the progeny.

There are two diploid species used in the crosses that theoretically might come into contact with TKS: T. bicorne Dahlst. and T. multiscaposum Schischk. However, in the field we did not find any co-occurrence of the latter two taxa with TKS (sympatry or parapatry) in spite of a detailed search of all the known macrolocalities of TKS, nor we observed any traces of hybridization in the field.

One of the triploid agamospermous pollen donors (from Kokpek, SE. Kazakhstan) used in experimental crosses.

Hybridization with agamospermous triploids and tetraploids, even in backcross generations, gives rise to hybrid seed set up to 10 %, rarely higher (in addition to autogamous TKS achenes due to Mentor Effect). Hybrids are triploid to pentaploid, agamospermous. Some of the paternal agamosperms are sympatric to parapatric to TKS (T. brevicorniculatum and T. kizil-sagyz sp. nova; in spite of the fact that no hybrids have been observed, there is a certain potential for hybridogeny. This is also supported by the fact that the genome of the hybridogenous triploid agamosperm T. brevicorniculatum includes the chromosome complement of TKS (P. van Dijk, unpublished).

The second approach involved sampling of natural populations where TKS coexisted with other native Kazakhstan dandelions (some of them having been used also in the first approach. At two localities in SE. Kazakhstan, we sampled TKS growing in mixed stands with other dandelions, agamospermous polyploids. Although, there was a morphological trait indication of possible hybridization, the molecular analyses (KASP, see below) definitely excluded gene flow within the two mixed populations.

One of the TKS sites along Kegen River, SE. Kazakhstan

And last, we visited historical sites of TKS cultivation in Europe (Sweden) to look for the evidence of the past gene flow (introgression). During the years of cultivation, millions of achenes of TKS flowed to the vicinity of fields, and vice versa, billions of pollen grains were transferred to and from the TKS flower capitula. Kompetitive allele specific PCR (KASP) markers were used to detect specific parts of TKS genome in hundreds of plants sampled in Skåne, Sweden. No clear evidence of gene flow has been obtained up to now. However, further analysis of a single suspicious specimen is in progress.

A well developed T. koksaghyz (morphotype with a distinctive leaf shape; Tuzkol, SE. Kazakhstan)

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