Genome size variation among common dandelion accessions informs their mode of reproduction and suggests the absence of sexual diploids in North America

Abstract

Apomixis is the ability of plants to produce asexual seeds, which are clones of the mother plant. The phenomenon of apomixis is tightly linked to ploidy, where diploids lack apomixis and reproduce sexually, while higher ploidy levels can exhibit apomixis. Taraxacum F.H.Wigg. species (dandelions) commonly exhibit apomixis; however, only limited studies have evaluated genome size variation of the iconic weedy dandelion, Taraxacum officinale F.H.Wigg. (common dandelion), particularly in North America. To evaluate the ploidy and reproductive biology of common dandelion, we created a global collection, with an emphasis on North America and determined genome size by evaluating seeds with flow cytometry. A total of 635 accessions were screened, and with the exception of two accessions from Germany and Austria, all were found to exclusively contain polyploid seed. The mode of reproduction of a sample of 96 of these accessions was observed by conducting emasculations. Our results indicate that the diploid, sexual cytotype of common dandelion may be absent in North America, while diploids were found in previously described areas of Central Europe. This suggests that the clonal lineages of common dandelion in North America may largely be derivative from apomictic plants introduced from abroad. Furthermore, if all North American common dandelion is apomictic, it may be unreceptive to pollen, which may isolate it from other dandelion species and inform the potential for gene flow.