Hybridization potential between the rubber dandelion Taraxacum kok‐saghyz and common dandelion Taraxacum officinale

Taraxacum kok‐saghyz (TK) is a species of dandelion that is of interest commercially for the high‐quality rubber produced in its roots; however, TK competes poorly with weeds. In order to overcome this shortcoming, there is interest in developing herbicide‐resistant TK germplasm by a variety of means, including selection, transgene insertion, and gene editing. The potential release of such germplasm raises the question of gene flow between TK and its ubiquitous weedy relative, the common dandelion, Taraxacum officinale (TO). The potential for introgression may be influenced by the reproductive biology of TO, which can exist as a diploid sexual or polyploid obligate apomict. In North America, only polyploid, apomictic TO has been described. As weedy TO types exhibit obligate apomixis, they are expected to be unreceptive to TK pollen; however, it may still be possible for them to pollinate TK. To this end, unidirectional crosses were conducted and progeny were evaluated with molecular markers. Taraxacum officinale pollen used to fertilize TK flowers produced low seed set and seeds with a low germination rate. However, 23% of rare viable progeny proved to be the result of true hybridization. Outdoor TK seed production areas heavily contaminated with TO were also screened for naturally occurring hybridization during a three‐year period using a combined strategy of both phenotyping (~3.35 million plants) and genotyping. Hybrids were detected during one of these years, at a rate of 1 in 100,000, when pollination was augmented with beehives. Hybrids from controlled crosses exhibited TO characteristics, such as lacerate leaves and apomixis. Some apomictic hybrids were able to produce viable seeds, whereas non‐apomicts were sterile. Seeds produced by apomictic hybrids demonstrated the ability to establish and produce apomictic progeny when in competition with perennial ryegrass. The prevalence of apomixis in TO may limit subsequent pollen‐mediated gene flow and introgression, but more work is needed to understand the longevity of apomictic hybrids under natural conditions.